Re: palindrome iteration
This whole conversation got interesting, so I thought I'd run some
speed tests:
The code:
from timeit import Timer
def is_palindrome_recursive(s):
if len(s) <= 1:
return True
if s[0] != s[-1]:
return False
else:
return is_palindrome(s[1:-1])
def is_palindrome_slice(s):
return s == s[::-1]
def is_palindrome_list(s):
l = list(s)
l.reverse()
return s == ''.join(l)
def is_palindrome_reversed(s):
return s == ''.join(reversed(s))
t = Timer("is_palindrome_recursive('madamimadam')", "from __main__
import is_palindrome_recursive")
print "is_palindrome_recursive", min(t.repeat())
t = Timer("is_palindrome_slice('madamimadam')", "from __main__ import
is_palindrome_slice")
print "is_palindrome_slice", min(t.repeat())
t = Timer("is_palindrome_list('madamimadam')", "from __main__ import
is_palindrome_list")
print "is_palindrome_list", min(t.repeat())
t = Timer("is_palindrome_reversed('madamimadam')", "from __main__
import is_palindrome_reversed")
print "is_palindrome_reversed", min(t.repeat())
The results:
is_palindrome_recursive 6.32680866827
is_palindrome_slice 1.23618350114
is_palindrome_list 4.60104846653
is_palindrome_reversed 5.99355296513
The slice method is uglier, I have to admit, but it's the fastest of
these four on my machine.
Josh
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Re: looking for open source python project
On Sun, Aug 29, 2010 at 6:20 AM, mo reina wrote: > looking for a python project (preferably something a bit small) that > is looking for contributors. the small bit is because i've never > worked in a team before and haven't really read source code that's > 1000s of lines long, so i'm not too sure i can keep up. > > my python fu is decent (i think), i recently wrote a small archive/ > grimoire program (command line only) that can store multiline text > with title, tags, and basic search functionality (not using curses so > the entry, once entered, can't be modified), entries are stored in a > pickle file. > > anybody have any suggestions? i'm keen to work on something with > others, both for learning and i'd like to do something a bit > meaningful, plus i'm sure it's fun. You can take a look at http://openhatch.org/ -- regards, kushal -- http://mail.python.org/mailman/listinfo/python-list
comp.lang.python
www.127760.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem checking an existing browser cookie
On 28 Αύγ, 23:07, Peter Otten <__pete...@web.de> wrote:
> Νίκος wrote:
> > On 22 Αύγ, 10:27, Νίκος wrote:
> >> On 16 Αύγ, 14:31, Peter Otten <__pete...@web.de> wrote:
> >> > Νίκος wrote:
> >> > > # initializecookie
> >> > >cookie=Cookie.SimpleCookie()
> >> > >cookie.load( os.environ.get('HTTP_COOKIE', '') )
> >> > > mycookie =cookie.get('visitor')
>
> >> > > if ( mycookie and mycookie.value != 'nikos' ) or re.search( r'(cyta|
> >> > > yandex|13448|spider|crawl)', host ) is None:
> >> > > blabla...
> >> > >
>
> >> > > I checked and Chrome has acookienames visitor with a value ofnikos
> >> > > within.
> >> > > So, i have to ask why the if fails?
>
> >> > Maybe it's because != != ==
>
> >> Iwant ti if code block to be executed only if the browsercookienames
> >> visitor fetched doesnt cotnain the vbalue of 'nikos'
>
> >> Is there somethign wrong with the way i wrote it?
>
> > Please do help me with this too becaus eif i dont solve this my
> > website keeps count my each visit like iam a guest visitor!
>
> In your initial post it sounded like you wanted the if-branch to execute for
> a user named "nikos", but now it seems that I misunderstood you and swapping
> 'mycookie.value != "nikos"' for 'mycookie.value == "nikos"' won't help.
> Maybe you could add a print statement like
>
> print mycookie.value
>
> to start with your debugging efforts.
>
> Peter
Maybe
> # initialize cookie
> cookie = Cookie.SimpleCookie()
> cookie.load( os.environ.get('HTTP_COOKIE', '') )
> mycookie = cookie.get('visitor')
wont load the cookie correctly? because
print mycookie.value
outputs an error.
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Re: Problem checking an existing browser cookie
On 28 Αύγ, 23:15, MRAB wrote:
> On 28/08/2010 20:37, Íßêïò wrote:
>
>
>
>
>
>
>
>
>
> > On 22 Áýã, 10:27, Íßêïò wrote:
> >> On 16 Áýã, 14:31, Peter Otten<__pete...@web.de> wrote:
>
> >>> Íßêïò wrote:
> # initializecookie
> cookie=Cookie.SimpleCookie()
> cookie.load( os.environ.get('HTTP_COOKIE', '') )
> mycookie =cookie.get('visitor')
>
> if ( mycookie and mycookie.value != 'nikos' ) or re.search( r'(cyta|
> yandex|13448|spider|crawl)', host ) is None:
> blabla...
>
>
> I checked and Chrome has acookienames visitor with a value ofnikos
> within.
> So, i have to ask why the if fails?
>
> >>> Maybe it's because != != ==
>
> >> Iwant ti if code block to be executed only if the browsercookienames
> >> visitor fetched doesnt cotnain the vbalue of 'nikos'
>
> >> Is there somethign wrong with the way i wrote it?
>
> > Please do help me with this too becaus eif i dont solve this my
> > website keeps count my each visit like iam a guest visitor!
>
> Print out mycookie, repr(mycookie.value) (unless mycookie is None) and
> repr(host). Then follow the code yourself to see whether the condition
> is True.
print mycookie outputs 'None'
Thts weird because i check with the browser and the cookie is there!
print repr(host) outputs '78-236-176.adsl.cyta.gr'
repr(mycookie.value) (unless mycookie is None)
and also
print mycookie.value gives an error too. Maybe there is not a value
method?
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Re: String substitution VS proper mysql escaping
On 28 Αύγ, 23:12, MRAB wrote:
> On 28/08/2010 20:51, Νίκος wrote:
>
>
>
>
>
>
>
>
>
> > On 28 Αύγ, 22:35, MRAB wrote:
>
> >> """When there's more than one value you provide a tuple. It's makes sense
> >> from the point of view of consistency that you also provide a tuple when
> >> there's only one value."""
>
> > Can you write something that make use of more than one value?
>
> > Perhaps you mena somethign like?
>
> > cursor.execute( '''SELECT hits FROM counters WHERE page = %s and date
> > = %s and host = %s''' , (page,) )
>
> > Is this what you mean?
>
> > All those special format strign identifiers will grab their values out
> > of the tuple?
>
> Your example contains 3 placeholders, so it needs 3 values:
>
> cursor.execute('''SELECT hits FROM counters WHERE page = %s and
> date = %s and host = %s''', (page, date, host))
>
> This will be safe. Any quoting that's needed will be done by .execute().
Will this also work without the parentheses?
> cursor.execute('''SELECT hits FROM counters WHERE page = %s and
> date = %s and host = %s''', page, date, host)
or python will not allow it cause it might think there are 4 args
isntead of two?
> cursor.execute(''' SELECT hits FROM counters WHERE page = '%s' and
> date = '%s' and host = '%s' ''', (page, date, host))
Whats happens if i attempt to also quote by single or double quoting
the above although now i'm aware that .execute method does the quoting
for me?
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Re: Tag parsing in python
On Aug 28, 11:14 am, agnibhu wrote:
> Hi all,
>
> I'm a newbie in python. I'm trying to create a library for parsing
> certain keywords.
> For example say I've key words like abc: bcd: cde: like that... So the
> user may use like
> abc: How are you bcd: I'm fine cde: ok
>
> So I've to extract the "How are you" and "I'm fine" and "ok"..and
> assign them to abc:, bcd: and cde: respectively.. There may be
> combination of keyowords introduced in future. like abc: xy: How are
> you
> So new keywords qualifying the other keywords so on..
> So I would like to know the python way of doing this. Is there any
> library already existing for making my work easier. ?
>
> ~
> Agnibhu
Here's how pyparsing can parse your keyword/tags:
from pyparsing import Combine, Word, alphas, Group, OneOrMore, empty,
SkipTo, LineEnd
text1 = "abc: How are you bcd: I'm fine cde: ok"
text2 = "abc: xy: How are you"
tag = Combine(Word(alphas)+":")
tag_defn = Group(OneOrMore(tag))("tag") + empty + SkipTo(tag |
LineEnd())("body")
for text in (text1,text2):
print text
for td in tag_defn.searchString(text):
print td.dump()
print
Prints:
abc: How are you bcd: I'm fine cde: ok
[['abc:'], 'How are you']
- body: How are you
- tag: ['abc:']
[['bcd:'], "I'm fine"]
- body: I'm fine
- tag: ['bcd:']
[['cde:'], 'ok']
- body: ok
- tag: ['cde:']
abc: xy: How are you
[['abc:', 'xy:'], 'How are you']
- body: How are you
- tag: ['abc:', 'xy:']
Now here's how to further use pyparsing to actually use those tags as
substitution macros:
from pyparsing import Forward, MatchFirst, Literal, And, replaceWith,
FollowedBy
# now combine macro detection with substitution
macros = {}
macro_substitution = Forward()
def make_macro_sub(tokens):
macros[tuple(tokens.tag)] = tokens.body
# define macro substitution
macro_substitution << MatchFirst(
[(Literal(k[0]) if len(k)==1
else And([Literal(kk) for kk in
k])).setParseAction(replaceWith(v))
for k,v in macros.items()] ) + ~FollowedBy(tag)
return ""
tag_defn.setParseAction(make_macro_sub)
scan_pattern = macro_substitution | tag_defn
test_text = text1 + "\nBob said, 'abc:?' I said, 'bcd:.'" + text2 +
"\nThen Bob said 'abc: xy:?'"
print test_text
print scan_pattern.transformString(test_text)
Prints:
abc: How are you bcd: I'm fine cde: ok
Bob said, 'abc:?' I said, 'bcd:.'abc: xy: How are you
Then Bob said 'abc: xy:?'
Bob said, 'How are you?' I said, 'I'm fine.'
Then Bob said 'How are you?'
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Re: Fibonacci: How to think recursively
On Sat, Aug 28, 2010 at 7:25 PM, Steven D'Aprano wrote: > On Sat, 28 Aug 2010 16:12:36 -0700, Baba wrote: >> Level: beginner >> >> I would like to know how to approach the following Fibonacci problem: >> my attempted rough code: >> >> def fibonacci(n): >> # base case: >> result = fibonacci (n-1) + fibonacci (n-2) this will end up in a mess as it will create overlapping recursions > > Mathematically, there is nothing wrong with overlapping recursion. It > will work, and Python can handle it easily. > > But in practical terms, it can lead to great inefficiency. In this > example, it should be avoided because it is slow. Very slow. To calculate > the nth Fibonacci number using naive recursion requires *many* calls: > > fib(4) # first call > => fib(3) + fib(2) # three calls > => fib(2) + fib(1) + fib(1) + fib(0) # seven calls > => fib(1) + fib(0) + 1 + 1 + 0 # nine calls > => 1 + 0 + 1 + 1 + 0 = 3 > > So to get fib(4) = 3 requires nine calls to fib(). > > This growth function doesn't have a name (as far as I know), It's A001595 in OEIS; http://www.research.att.com/~njas/sequences/A001595 "Sometimes called 'Leonardo numbers'" Also apparently "2-ranks of difference sets constructed from Segre hyperovals." > but it grows > much faster than fib() itself: > > n = 0 1 2 3 4 5 6 ... 35 ... > fib(n) = 0 1 1 2 3 5 8 ... 9227465 ... > calls = 1 1 3 5 9 15 25 ... 29860703 ... > > As you can see, the number of calls is also calculable by a recursive > expression R: > > R(0) = R(1) = 1 > R(n) = R(n-1) + R(n-2) + 1 > > This is very similar to the Fibonacci recursion, only it grows more > quickly. But I digress... Other formulations courtesy OEIS: R(n) = sum(fib(i) for i in range(1, n+1)) - fib(n-1) R(n) = 2*fib(n+1) - 1 Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Fibonacci: How to think recursively
"Steven D'Aprano" wrote in message news:4c79c510$0$28655$c3e8...@news.astraweb.com... On Sat, 28 Aug 2010 16:12:36 -0700, Baba wrote: There are other techniques, but this will do to get started. Once you realize recursion for Fibonacci numbers is still fairly slow, look up generator functions :^) -Mark -- http://mail.python.org/mailman/listinfo/python-list
Re: Functional composition in python
On Aug 29, 5:14 am, Steven D'Aprano wrote:
> On Sat, 28 Aug 2010 21:30:39 +0400, Dmitry Groshev wrote:
> > Hello all. Some time ago I wrote a little library:
> >http://github.com/si14/python-functional-composition/, inspired by
> > modern functional languages like F#. In my opinion it is quite useful
> > now, but I would like to discuss it.
> > An example of usage:
>
> > import os
> > from pyfuncomp import composable, c, _
>
> > def comment_cutter(s):
> > t = s.find("#")
> > return s if t < 0 else s[0:t].strip()
>
> > @composable #one can use a decorator to make a composable function
> > def empty_tester(x):
> > return len(x) > 0 and x[0] != "#"
>
> Why do you need a decorator to make a composable function? Surely all
> functions are composable -- it is the nature of functions that you can
> call one function with the output of another function.
>
>
>
> > path_prefix = "test"
>
> > config_parser = (c(open) >> #or use a transformer function
> > c(str.strip).map >> #"map" acts like a function modifier
> > c(comment_cutter).map >>
> > empty_tester.filter >> #so does "filter"
> > c(os.path.join)[path_prefix, _].map) #f[a, _, b] is
> > used to make a partial.
> > #f[a, foo:bar,
> > baz:_] is also correct
>
> > print config_parser("test.txt")
> > print (c("[x ** %s for x in %s]")[2, _] << c(lambda x: x * 2).map)([1,
> > 2, 3])
>
> > Any suggestions are appreciated.
>
> Did you expect us to guess what the above code would do? Without showing
> the output, the above is just line noise.
>
> What does c() do? What does compose() do that ordinary function
> composition doesn't do? You say that "map" acts as a function modifier,
> but don't tell us *what* it modifies or in what way. Same for filter.
>
> So anyone not familiar with C syntax, the use of << is just line noise.
> You need to at say what you're using it for.
>
> --
> Steven
Yep, it's my mistake. I thought this syntax is quite intuitive. Here
is some explanations in code:
@composable
def f1(x):
return x * 2
@composable
def f2(x):
return x + 3
@composable
def f3(x):
return (-1) * x
@composable
def f4(a):
return a + [0]
@composable
def sqrsum(x, y):
return x ** 2 + y ** 2
print f1(2) #4
print f2(2) #5
print (f1 << f2 << f1)(2) #14
print (f3 >> f2)(2) #1
print (f2 >> f3)(2) #-5
print (c(float) << f1 << f2)(4) #14.0
print (sqrsum[_, 1] << f1)(2) #17
print (sqrsum[_, _].map)([1, 2, 3, 4, 5]) #[2, 8, 18, 32, 50]
print (c(lambda x: x * 2).map >> c("[x * %s for x in %s]")[3, _])([1,
2, 3]) #[6, 12, 18]
Generally, f1 >> f2 means "lambda x: f2(f1(x))" or "pass the result of
f1 to f2". But in python function can return only one value, so a
composable function should be a function of one argument. So some form
of making partial is needed, and here comes a
f[a, b, _] notation, which means "substitute 3rd argument of f, first
twos are a and b". Finally, we need some form of syntactic sugar for
this: c(map)[c(f),_], so we have a "map" modifier, which transforms
function F to an isomorphism or mapping between lists. For example,
c(lambda x: x * 2).map is equal to lambda x: map(lambda y: y * 2, x).
"Filter" modifier is the same thing for boolean functions.
>What does c() do? What does compose() do that ordinary function
>composition doesn't do?
I need c() or composable() to make an objects with overloaded
operators.
All in all, all this stuff is just a syntactic sugar for nested
functions, maps and filters, which brings a new semantics for old
operators (so one can call it edsl).
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Re: Fibonacci: How to think recursively
On Sat, 28 Aug 2010 16:12:36 -0700, Baba wrote: > Level: beginner > > I would like to know how to approach the following Fibonacci problem: > How may rabbits do i have after n months? > > I'm not looking for the code as i could Google that very easily. I'm > looking for a hint to put me on the right track to solve this myself > without looking it up. > > my brainstorming so far brought me to a stand still as i can't seem to > imagine a recursive way to code this: Perhaps you need to start with a simpler case to get your head around the ideas. Let's look at factorial first. fact(n) = n*(n-1)*(n-2)*(n-3)*...*2*1 Working upwards: fact(0) = 1 # this is by definition. fact(1) = 1 # also by definition. fact(2) = 2*1 = 2*fact(1) fact(3) = 3*2*1 = 3*fact(2) ... fact(n) = n*fact(n-1) So now you have the base case: if n is 1 or smaller, fact(n) returns 1 and the recursive case: otherwise fact(n) returns n*fact(n-1) Now write that as a Python function, and test it to see that it is correct. Come back once you've got it working satisfactorily. Now, can you apply the same reasoning to the Fibonacci problem? What is your base case? You need some way to halt the recursion, something that *doesn't* make a recursive call. def fib(n): if SOME_CONDITION: return SOME_VALUE else: return SOME_RECURSION is the most basic form you can have. Notice that you must *return* something. That's basic Python syntax -- if you don't call return, the function will return the special None object, which is not what you want. More generally, you could have multiple base cases and multiple recursive cases, not necessarily one of each. But there must be at least one non- recursive expression that gets returned, or the recursion can never terminate. > my attempted rough code: > > def fibonacci(n): > # base case: > result = fibonacci (n-1) + fibonacci (n-2) >>> this will end up in a mess as it will create overlapping recursions Mathematically, there is nothing wrong with overlapping recursion. It will work, and Python can handle it easily. But in practical terms, it can lead to great inefficiency. In this example, it should be avoided because it is slow. Very slow. To calculate the nth Fibonacci number using naive recursion requires *many* calls: fib(4)# first call => fib(3) + fib(2)# three calls => fib(2) + fib(1) + fib(1) + fib(0) # seven calls => fib(1) + fib(0) + 1 + 1 + 0# nine calls => 1 + 0 + 1 + 1 + 0 = 3 So to get fib(4) = 3 requires nine calls to fib(). This growth function doesn't have a name (as far as I know), but it grows much faster than fib() itself: n = 0 1 2 3 4 5 6 ... 35 ... fib(n) = 0 1 1 2 3 5 8 ... 9227465 ... calls = 1 1 3 5 9 15 25 ... 29860703 ... As you can see, the number of calls is also calculable by a recursive expression R: R(0) = R(1) = 1 R(n) = R(n-1) + R(n-2) + 1 This is very similar to the Fibonacci recursion, only it grows more quickly. But I digress... You can make the recursive version more efficient if you give it a memory. In the call to fib(5), for example, it ends up calling fib(4) once, fib(3) twice, fib(2) three times, fib(1) four times, and fib(0) twice. If it could remember each value once it saw it, it could potentially save nine calls (out of fifteen). That's a less inefficient use of recursion. Think about ways to give it a short-term memory. You can make it even more efficient by giving fib() a long-term cache, so that each call to fib(5) requires one cache lookup rather than six (or fifteen) recursive calls. Other than the first time, obviously. This is called memoisation, but again I digress. There are other techniques, but this will do to get started. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Functional composition in python
On Sat, 28 Aug 2010 21:30:39 +0400, Dmitry Groshev wrote:
> Hello all. Some time ago I wrote a little library:
> http://github.com/si14/python-functional-composition/ , inspired by
> modern functional languages like F#. In my opinion it is quite useful
> now, but I would like to discuss it.
> An example of usage:
>
> import os
> from pyfuncomp import composable, c, _
>
> def comment_cutter(s):
> t = s.find("#")
> return s if t < 0 else s[0:t].strip()
>
> @composable #one can use a decorator to make a composable function
> def empty_tester(x):
> return len(x) > 0 and x[0] != "#"
Why do you need a decorator to make a composable function? Surely all
functions are composable -- it is the nature of functions that you can
call one function with the output of another function.
> path_prefix = "test"
>
> config_parser = (c(open) >> #or use a transformer function
> c(str.strip).map >> #"map" acts like a function modifier
> c(comment_cutter).map >>
> empty_tester.filter >> #so does "filter"
> c(os.path.join)[path_prefix, _].map) #f[a, _, b] is
> used to make a partial.
> #f[a, foo:bar,
> baz:_] is also correct
>
> print config_parser("test.txt")
> print (c("[x ** %s for x in %s]")[2, _] << c(lambda x: x * 2).map)([1,
> 2, 3])
>
> Any suggestions are appreciated.
Did you expect us to guess what the above code would do? Without showing
the output, the above is just line noise.
What does c() do? What does compose() do that ordinary function
composition doesn't do? You say that "map" acts as a function modifier,
but don't tell us *what* it modifies or in what way. Same for filter.
So anyone not familiar with C syntax, the use of << is just line noise.
You need to at say what you're using it for.
--
Steven
--
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Re: palindrome iteration
On Sat, 28 Aug 2010 15:11:03 +0300, Jussi Piitulainen wrote: [...] > When I said that there could be such a method, I was merely objecting to > a statement, made in response to me, that there could not be such a > method because strings are immutable. You clearly agree with me that > that statement was not correct. Would you have let it stand if it was > made to you? Ha ha, you're new here aren't you? > To answer your question, I don't see a real need for .reversed() in > strings, but I do think .reversed() would be much more useful than > .swapcase() which is in Python now and for which I see no use at all. It's hard to disagree with that. I'm not entirely sure what the use-case for swapcase is. It's not quite as specialised as sTUdlEycApS but not far off. [...] > I agree that the gain would be minimal. There is no harm in the method > either, so I would not object to it if somebody were to propose its > addition, but just to clarify my position: I have not proposed it. Then we are in agreement :) I think the only thing we disagree on is that I think [::-1] is a perfectly nice expression for reversal, while you don't. True, it's not entirely intuitive to newbies, or self-documenting, you need to learn slicing to understand it. But then, if you were Dutch and had not learned English, you would probably be looking for a method called omgekeerde and would find reverse equally unintuitive. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
looking for open source python project
looking for a python project (preferably something a bit small) that is looking for contributors. the small bit is because i've never worked in a team before and haven't really read source code that's 1000s of lines long, so i'm not too sure i can keep up. my python fu is decent (i think), i recently wrote a small archive/ grimoire program (command line only) that can store multiline text with title, tags, and basic search functionality (not using curses so the entry, once entered, can't be modified), entries are stored in a pickle file. anybody have any suggestions? i'm keen to work on something with others, both for learning and i'd like to do something a bit meaningful, plus i'm sure it's fun. -- http://mail.python.org/mailman/listinfo/python-list
Re: Fibonacci: How to think recursively
I suggest you to memoize results in order to prevent overlapping recursion. Regards, Matteo On Sun, Aug 29, 2010 at 2:23 AM, Ben Finney wrote: > Baba writes: > >> my brainstorming so far brought me to a stand still as i can't seem to >> imagine a recursive way to code this: >> >> my attempted rough code: >> >> def fibonacci(n): >> # base case: >> result = fibonacci (n-1) + fibonacci (n-2) >> >> this will end up in a mess as it will create overlapping recursions > > It also never returns anything (which, in Python, means it returns the > None object). > > Worse, it will endlessly recurse; every time it's called it will call > itself (twice). > > Perhaps a way to approach the problem is: How will your function know > when *not* to call itself? What will it do instead? Try writing that > case first, and then write the rest of it on that basis. > > -- > \ “Science is a way of trying not to fool yourself. The first | > `\ principle is that you must not fool yourself, and you are the | > _o__) easiest person to fool.” —Richard P. Feynman, 1964 | > Ben Finney > -- > http://mail.python.org/mailman/listinfo/python-list > -- Matteo Landi http://www.matteolandi.net/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Fibonacci: How to think recursively
Baba writes: > my brainstorming so far brought me to a stand still as i can't seem to > imagine a recursive way to code this: > > my attempted rough code: > > def fibonacci(n): > # base case: > result = fibonacci (n-1) + fibonacci (n-2) > >> this will end up in a mess as it will create overlapping recursions It also never returns anything (which, in Python, means it returns the None object). Worse, it will endlessly recurse; every time it's called it will call itself (twice). Perhaps a way to approach the problem is: How will your function know when *not* to call itself? What will it do instead? Try writing that case first, and then write the rest of it on that basis. -- \ “Science is a way of trying not to fool yourself. The first | `\ principle is that you must not fool yourself, and you are the | _o__) easiest person to fool.” —Richard P. Feynman, 1964 | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: InteractiveConsole and namespace
On Sat, Aug 28, 2010 at 2:37 PM, David ROBERT wrote: > Hi all, > > I want to use an InteractiveConsole at some stage in a program to > interact with the local namespace: access, but also modify objects. > When the interactive console ends (ctrl-d) I want the program to > continue processing with the variables that may have been modified > interactively. > > The code below works (block invoking the console is not in a > function). During the interactive session, I can read value of a, I > can change value of a and the new value is "updated" in the block > namespace. > > import code > if __name__ == '__main__': > a=1 > c = code.InteractiveConsole(locals()) > c.interact() # Here I interactively change the value of a (a=2) > print "Value of a: ", a > > print returns --> Value of a: 2 > > However, on the other code below (the console is invoked from within a > function block), during the interactive session, I can read value of > a, I can change value of a. But the local namespace of the function is > not updated: > > import code > def test(): > a=1 > c = code.InteractiveConsole(locals()) > c.interact() # Here I interactively change the value of a (a=2) > print "Value of a: ", a > > if __name__ == '__main__': > test() > > print returns --> Value of a: 1 > > I need to run the InteractiveConsole from a function block. I tried > different things with the local and parent frames (sys._getframe()) > but nothing successful. If I put a in the global namespace it works, > but I would like to [...] > understand what the > problem is. Read http://docs.python.org/library/functions.html#locals (emphasis added): "locals() [...] Note: The contents of this dictionary should not be modified; ***changes may not affect the values of local and free variables used by the interpreter***." At the top-level / module scope, it just so happens that `locals() is globals() == True`; and unlike locals(), globals() does not have the aforequoted limitation. I don't know if there's a non-ugly workaround. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Fibonacci: How to think recursively
Baba wrote: > Level: beginner > > I would like to know how to approach the following Fibonacci problem: > How may rabbits do i have after n months? > > I'm not looking for the code as i could Google that very easily. I'm > looking for a hint to put me on the right track to solve this myself > without looking it up. > > my brainstorming so far brought me to a stand still as i can't seem to > imagine a recursive way to code this: > > my attempted rough code: > > def fibonacci(n): > # base case: > result = fibonacci (n-1) + fibonacci (n-2) >>> this will end up in a mess as it will create overlapping recursions I don't think this is the base case. The base case would be one or more values of `n` that you already know the fibonacci number for. Your recursive function can just test for those and return the right answer right away. The the expression you've coded contains a good way to handle the non-base cases. There's no such problem as "overlapping recursions". Mel. -- http://mail.python.org/mailman/listinfo/python-list
Fibonacci: How to think recursively
Level: beginner I would like to know how to approach the following Fibonacci problem: How may rabbits do i have after n months? I'm not looking for the code as i could Google that very easily. I'm looking for a hint to put me on the right track to solve this myself without looking it up. my brainstorming so far brought me to a stand still as i can't seem to imagine a recursive way to code this: my attempted rough code: def fibonacci(n): # base case: result = fibonacci (n-1) + fibonacci (n-2) >> this will end up in a mess as it will create overlapping recursions OR def fibonacci(n): # base case: fibonacci(n+2) - fibonacci(n+1) - n = 0 >> this too would create overlapping recursions How to go about this? Thanks Baba -- http://mail.python.org/mailman/listinfo/python-list
Helper app for intranet site
I'm exploring the possibility of developing a helper app for an existing internal company website. Basically, it would automatically scan the current page contents, including prepopulated forms, and provide context-related business rule comments to the user, via a stay- on-top wxPython panel. Any suggestions on how to do this? (The web developers are unavailable to do this within the site.) Thanks, Kevin -- http://mail.python.org/mailman/listinfo/python-list
Re: Tag parsing in python
On Aug 28, 9:14 am, agnibhu wrote: > Hi all, > > I'm a newbie in python. I'm trying to create a library for parsing > certain keywords. > For example say I've key words like abc: bcd: cde: like that... So the > user may use like > abc: How are you bcd: I'm fine cde: ok > > So I've to extract the "How are you" and "I'm fine" and "ok"..and > assign them to abc:, bcd: and cde: respectively.. There may be > combination of keyowords introduced in future. like abc: xy: How are > you > So new keywords qualifying the other keywords so on.. > So I would like to know the python way of doing this. Is there any > library already existing for making my work easier. ? > > ~ > Agnibhu Have you looked at pyparsing? (http://pyparsing.wikispaces.com/) It may be possible to use that library to do this. Josh -- http://mail.python.org/mailman/listinfo/python-list
Re: pyxser-1.5r --- Python Object to XML serializer/deserializer
On Aug 26, 10:02 pm, Stefan Behnel wrote: > Josh English, 27.08.2010 01:30: > > > solve a lot of the problems I'm running into in my own attempt to > > build a python Class implementation of an XML Validation object. > > How would object serialisation help here? > > I'm running into the same problem in a lot of projects I'm working on. I can't decide one the best way to serialize instances of classes. I want to be able to store these instances in a human-readable and editable format that I can reload back into their objects. The XML validation tool requires the rules of the XML to be written out in Python as classes and instances. I would love to have a consistent way to write the definition file and load it. For example, Relax NG can be written out, the rules loaded into a parser, and actual XML data can be validated against it. Since I started in Python, I want that bridge back to serialization. In this project, and others, subclassing plays a big role in using the code, so I need a reliable way of writing a definition, loading it into the proper subclass, and running with those subclasses. I am familiar with XML, but I've played with YAML and may try that. I'm hesitant to use YAML because it requires that I add the YAML.object. I even wrote a program to store data similar to GEDCOM format, which seemed the simplest from a user's perspective. Josh -- http://mail.python.org/mailman/listinfo/python-list
InteractiveConsole and namespace
Hi all, I want to use an InteractiveConsole at some stage in a program to interact with the local namespace: access, but also modify objects. When the interactive console ends (ctrl-d) I want the program to continue processing with the variables that may have been modified interactively. The code below works (block invoking the console is not in a function). During the interactive session, I can read value of a, I can change value of a and the new value is "updated" in the block namespace. import code if __name__ == '__main__': a=1 c = code.InteractiveConsole(locals()) c.interact() # Here I interactively change the value of a (a=2) print "Value of a: ", a print returns --> Value of a: 2 However, on the other code below (the console is invoked from within a function block), during the interactive session, I can read value of a, I can change value of a. But the local namespace of the function is not updated: import code def test(): a=1 c = code.InteractiveConsole(locals()) c.interact() # Here I interactively change the value of a (a=2) print "Value of a: ", a if __name__ == '__main__': test() print returns --> Value of a: 1 I need to run the InteractiveConsole from a function block. I tried different things with the local and parent frames (sys._getframe()) but nothing successful. If I put a in the global namespace it works, but I would like to find a nicer solution and also understand what the problem is. Thanks for any help -- David ROBERT http://blog.ombrepixel.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Jussi Piitulainen wrote: Steven D'Aprano writes: On Sat, 28 Aug 2010 09:22:13 +0300, Jussi Piitulainen wrote: Terry Reedy writes: On 8/27/2010 3:43 PM, Jussi Piitulainen wrote: Dave Angel writes: There could easily be a .reverse() method on strings. It would return the reversed string, like .swapcase() returns the swapcased string. Could be, but the main use case seems to be for palindrome testing ;-) Given that slicing and reversed() can do the same thing, the need is thin. The need is quite thin, but immutability of strings is not an issue, just like there can be .swapcase() though strings are immutable. That is all I am saying above. You're right, there could be a reversed() method for strings. There could also be a disemvowel method that removes vowels, a randomise method that shuffles the letters around, a studlycaps method that changes the case of each letter randomly, and a method to check that brackets () are well- formed. They would all be useful to somebody. There are lots of different methods that strings could have. Where do you draw the line? When I said that there could be such a method, I was merely objecting to a statement, made in response to me, that there could not be such a method because strings are immutable. You clearly agree with me that that statement was not correct. Would you have let it stand if it was made to you? Since you repeat that assertion three times, I figure you must think it's important. And it was I who asserted that a reverse() method wouldn't be possible on an immutable object. reverse() would reverse the characters in place, and return None. At least it would if it tried to be at all consistent with the list, array, and audioop methods of the same name. reversed() is certainly possible, and it'd make a new string with the reverse order of the original. DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Reading the access attributes of directories in Windows
On Sat, Aug 28, 2010 at 05:07, Lawrence D'Oliveiro wrote: > In message , Rami > Chowdhury wrote: > >> On Wed, Aug 25, 2010 at 05:04, Lawrence D'Oliveiro >> wrote: >> >>> In message , Nobody wrote: >>> Having this as a separate permission allows normal users to add entries to log files but not to erase existing entries. >>> >>> Unix/Linux systems can do this already. >> >> Ooh, I didn't know that -- what combination of permissions would I >> have to use to get such an effect? > > No special permissions needed at all—just use the syslog(3) functions. > > And the nice thing is, you don’t have to know whether the system logs are > kept on the local machine or on a remote machine, or how different > categories of messages are divided up into different files, how log rotation > is done, or anything like that—it’s all transparent. Ah, thanks -- I think I'd misread your first post as indicating that that kind of "append" effect would work for any file. Apologies for the misunderstanding! -- Rami Chowdhury "Never assume malice when stupidity will suffice." -- Hanlon's Razor 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD) -- http://mail.python.org/mailman/listinfo/python-list
Re: Reading the access attributes of directories in Windows
On Fri, Aug 27, 2010 at 14:16, Nobody wrote: > On Fri, 27 Aug 2010 13:28:46 +0600, Rami Chowdhury wrote: > Having this as a separate permission allows normal users to add entries to log files but not to erase existing entries. >>> >>> Unix/Linux systems can do this already. >> >> Ooh, I didn't know that -- what combination of permissions would I have to >> use to get such an effect? > > You can't do it with permissions, you need to use ext2 attributes. > Specifically, "chattr +a " will set the "append" attribute, > which prevents the file being opened for write except in append mode. > Changing this attribute requires root privilege or the CAP_LINUX_IMMUTABLE > capability. Fascinating, thank you! -- Rami Chowdhury "Never assume malice when stupidity will suffice." -- Hanlon's Razor 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD) -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem checking an existing browser cookie
On 28/08/2010 20:37, Νίκος wrote:
On 22 Αύγ, 10:27, Νίκος wrote:
On 16 Αύγ, 14:31, Peter Otten<__pete...@web.de> wrote:
Νίκος wrote:
# initializecookie
cookie=Cookie.SimpleCookie()
cookie.load( os.environ.get('HTTP_COOKIE', '') )
mycookie =cookie.get('visitor')
if ( mycookie and mycookie.value != 'nikos' ) or re.search( r'(cyta|
yandex|13448|spider|crawl)', host ) is None:
blabla...
I checked and Chrome has acookienames visitor with a value ofnikos
within.
So, i have to ask why the if fails?
Maybe it's because != != ==
Iwant ti if code block to be executed only if the browsercookienames
visitor fetched doesnt cotnain the vbalue of 'nikos'
Is there somethign wrong with the way i wrote it?
Please do help me with this too becaus eif i dont solve this my
website keeps count my each visit like iam a guest visitor!
Print out mycookie, repr(mycookie.value) (unless mycookie is None) and
repr(host). Then follow the code yourself to see whether the condition
is True.
--
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Re: Problem checking an existing browser cookie
Νίκος wrote:
> On 22 Αύγ, 10:27, Νίκος wrote:
>> On 16 Αύγ, 14:31, Peter Otten <__pete...@web.de> wrote:
>> > Νίκος wrote:
>> > > # initializecookie
>> > >cookie=Cookie.SimpleCookie()
>> > >cookie.load( os.environ.get('HTTP_COOKIE', '') )
>> > > mycookie =cookie.get('visitor')
>>
>> > > if ( mycookie and mycookie.value != 'nikos' ) or re.search( r'(cyta|
>> > > yandex|13448|spider|crawl)', host ) is None:
>> > > blabla...
>> > >
>>
>> > > I checked and Chrome has acookienames visitor with a value ofnikos
>> > > within.
>> > > So, i have to ask why the if fails?
>>
>> > Maybe it's because != != ==
>>
>> Iwant ti if code block to be executed only if the browsercookienames
>> visitor fetched doesnt cotnain the vbalue of 'nikos'
>>
>> Is there somethign wrong with the way i wrote it?
>
> Please do help me with this too becaus eif i dont solve this my
> website keeps count my each visit like iam a guest visitor!
In your initial post it sounded like you wanted the if-branch to execute for
a user named "nikos", but now it seems that I misunderstood you and swapping
'mycookie.value != "nikos"' for 'mycookie.value == "nikos"' won't help.
Maybe you could add a print statement like
print mycookie.value
to start with your debugging efforts.
Peter
--
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Re: String substitution VS proper mysql escaping
On 28/08/2010 20:51, Νίκος wrote:
On 28 Αύγ, 22:35, MRAB wrote:
"""When there's more than one value you provide a tuple. It's makes sense
from the point of view of consistency that you also provide a tuple when
there's only one value."""
Can you write something that make use of more than one value?
Perhaps you mena somethign like?
cursor.execute( '''SELECT hits FROM counters WHERE page = %s and date
= %s and host = %s''' , (page,) )
Is this what you mean?
All those special format strign identifiers will grab their values out
of the tuple?
Your example contains 3 placeholders, so it needs 3 values:
cursor.execute('''SELECT hits FROM counters WHERE page = %s and
date = %s and host = %s''', (page, date, host))
This will be safe. Any quoting that's needed will be done by .execute().
--
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Re: String substitution VS proper mysql escaping
On 28/08/2010 20:48, Νίκος wrote: On 28 Αύγ, 22:35, MRAB wrote: On 28/08/2010 20:10, Νίκος wrote:> On 20 Αύγ, 09:04, Nik Grwrote: With regard to the "%" operator, it considers the string on the left to be a format string with multiple %blah things in it to replace. The thing on the right is a sequence of items to place into the format string. Can you please clarify what you mean by that? Basically: format_string % (item_1, item_2, item_3) I still don't follow by means that i dotn see the point here... In you usage above you're supplying "page" instead of "(page,)". The latter matches the .execute() method's requirements. I tried it and "page" as a string and not a as a single element tuple works ok. Although the .execute() method might accept a single string: cursor.execute(sql_query, page) as well as a tuple containing the string: cursor.execute(sql_query, (page, )) try to be consistent. As I said before: """When there's more than one value you provide a tuple. It's makes sense from the point of view of consistency that you also provide a tuple when there's only one value.""" cursor.execute(sql_query, (page, )) is different than? cursor.execute(sql_query, page, ) ? Yes. The first has 2 arguments: a string and a tuple containing the value of 'page'. The second has 2 arguments: a string and the value of 'page'. === Why in mysql string substitution example i have to use page='%s' and in the comma way(automatic mysql convertion i dont need the single quotes and use it as page=%s ? What is the diff? === In the first case you're doing the substitution yourself, but you might not get it right, leaving your website open an SQL injection attacks. In the second case you're letting the .execute method do the substitution. It will have been written to do it correctly and safely. -- http://mail.python.org/mailman/listinfo/python-list
Re: String substitution VS proper mysql escaping
2010/8/29 Νίκος : > On 28 Αύγ, 22:35, MRAB wrote: > >> """When there's more than one value you provide a tuple. It's makes sense >> from the point of view of consistency that you also provide a tuple when >> there's only one value.""" > > Can you write something that make use of more than one value? > > > Perhaps you mena somethign like? > > cursor.execute( '''SELECT hits FROM counters WHERE page = %s and date > = %s and host = %s''' , (page,) ) > > Is this what you mean? > > All those special format strign identifiers will grab their values out > of the tuple? Yes, that's exactly right -- they'll try to grab values out of the tuple, and since in that particular code snippet the tuple doesn't contain enough items, you'll get an error :-) HTH, Rami -- Rami Chowdhury "Never assume malice when stupidity will suffice." -- Hanlon's Razor 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD) -- http://mail.python.org/mailman/listinfo/python-list
Re: String substitution VS proper mysql escaping
On 28 Αύγ, 22:35, MRAB wrote: > """When there's more than one value you provide a tuple. It's makes sense > from the point of view of consistency that you also provide a tuple when > there's only one value.""" Can you write something that make use of more than one value? Perhaps you mena somethign like? cursor.execute( '''SELECT hits FROM counters WHERE page = %s and date = %s and host = %s''' , (page,) ) Is this what you mean? All those special format strign identifiers will grab their values out of the tuple? -- http://mail.python.org/mailman/listinfo/python-list
Re: String substitution VS proper mysql escaping
On 28 Αύγ, 22:35, MRAB wrote: > On 28/08/2010 20:10, Νίκος wrote:> On 20 Αύγ, 09:04, Nik > Gr wrote: > >> With regard to the "%" operator, it considers the string on the left to > >> be a format string with multiple %blah things in it to replace. The > >> thing on the right is a sequence of items to place into the format > >> string. > > > Can you please clarify what you mean by that? > > Basically: > > format_string % (item_1, item_2, item_3) I still don't follow by means that i dotn see the point here... > > >> In you usage above you're supplying "page" instead of "(page,)". > >> The latter matches the .execute() method's requirements. > > > I tried it and "page" as a string and not a as a single element tuple > > works ok. > > Although the .execute() method might accept a single string: > > cursor.execute(sql_query, page) > > as well as a tuple containing the string: > > cursor.execute(sql_query, (page, )) > > try to be consistent. As I said before: > > """When there's more than one value you provide a tuple. It's makes sense > from the point of view of consistency that you also provide a tuple when > there's only one value.""" cursor.execute(sql_query, (page, )) is different than? cursor.execute(sql_query, page, ) ? === Why in mysql string substitution example i have to use page='%s' and in the comma way(automatic mysql convertion i dont need the single quotes and use it as page=%s ? What is the diff? === -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem checking an existing browser cookie
On 22 Αύγ, 10:27, Νίκος wrote:
> On 16 Αύγ, 14:31, Peter Otten <__pete...@web.de> wrote:
>
>
>
>
>
>
>
>
>
> > Νίκος wrote:
> > > # initializecookie
> > >cookie=Cookie.SimpleCookie()
> > >cookie.load( os.environ.get('HTTP_COOKIE', '') )
> > > mycookie =cookie.get('visitor')
>
> > > if ( mycookie and mycookie.value != 'nikos' ) or re.search( r'(cyta|
> > > yandex|13448|spider|crawl)', host ) is None:
> > > blabla...
> > >
>
> > > I checked and Chrome has acookienames visitor with a value ofnikos
> > > within.
> > > So, i have to ask why the if fails?
>
> > Maybe it's because != != ==
>
> Iwant ti if code block to be executed only if the browsercookienames
> visitor fetched doesnt cotnain the vbalue of 'nikos'
>
> Is there somethign wrong with the way i wrote it?
Please do help me with this too becaus eif i dont solve this my
website keeps count my each visit like iam a guest visitor!
--
http://mail.python.org/mailman/listinfo/python-list
Re: String substitution VS proper mysql escaping
On 28/08/2010 20:10, Νίκος wrote: On 20 Αύγ, 09:04, Nik Gr wrote: With regard to the "%" operator, it considers the string on the left to be a format string with multiple %blah things in it to replace. The thing on the right is a sequence of items to place into the format string. Can you please clarify what you mean by that? Basically: format_string % (item_1, item_2, item_3) In you usage above you're supplying "page" instead of "(page,)". The latter matches the .execute() method's requirements. I tried it and "page" as a string and not a as a single element tuple works ok. Although the .execute() method might accept a single string: cursor.execute(sql_query, page) as well as a tuple containing the string: cursor.execute(sql_query, (page, )) try to be consistent. As I said before: """When there's more than one value you provide a tuple. It's makes sense from the point of view of consistency that you also provide a tuple when there's only one value.""" -- http://mail.python.org/mailman/listinfo/python-list
Re: Functional composition in python
Dmitry Groshev wrote:
> Hello all. Some time ago I wrote a little library:
> http://github.com/si14/python-functional-composition/ , inspired by
> modern functional languages like F#. In my opinion it is quite useful
> now, but I would like to discuss it.
> An example of usage:
>
> import os
> from pyfuncomp import composable, c, _
>
> def comment_cutter(s):
> t = s.find("#")
> return s if t < 0 else s[0:t].strip()
>
> @composable #one can use a decorator to make a composable function
> def empty_tester(x):
> return len(x) > 0 and x[0] != "#"
>
> path_prefix = "test"
>
> config_parser = (c(open) >> #or use a transformer function
> c(str.strip).map >> #"map" acts like a function modifier
> c(comment_cutter).map >>
> empty_tester.filter >> #so does "filter"
> c(os.path.join)[path_prefix, _].map) #f[a, _, b] is
> used to make a partial.
> #f[a, foo:bar,
> baz:_] is also correct
>
> print config_parser("test.txt")
> Any suggestions are appreciated.
With some effort you could perhaps tweak your library to accept something
like
config_parser = c(open) | str.strip | comment_cutter | empty_tester |
c(os.path.join)(path_prefix, _)
This looks more like a shell pipe than a C++ print statement -- which I
think is a good thing.
More general: Yes, I know that the functional style is contagious. However,
I find that more traditional Python code is easier to understand. Compare:
import os
def config_parser(configfile, folder):
with open(configfile) as lines:
for line in lines:
name = line.partition("#")[0].strip()
if name:
yield os.path.join(folder, name)
for path in config_parser("test.txt", "test"):
print path
(at least that's what I'm guessing your code is trying to achieve)
Peter
--
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Re: String substitution VS proper mysql escaping
On 20 Αύγ, 09:04, Nik Gr wrote: > With regard to the "%" operator, it considers the string on the left to > be a format string with multiple %blah things in it to replace. The > thing on the right is a sequence of items to place into the format > string. Can you please clarify what you mean by that? > In you usage above you're supplying "page" instead of "(page,)". > The latter matches the .execute() method's requirements. I tried it and "page" as a string and not a as a single element tuple works ok. -- http://mail.python.org/mailman/listinfo/python-list
Re: Object containing a list of objects.
Chris I take good notice of your comments and suggestions. Thanks. -- http://mail.python.org/mailman/listinfo/python-list
Re: Object containing a list of objects.
Thanks MRAB and Peter Otten that solved the problem. -- http://mail.python.org/mailman/listinfo/python-list
Re: Object containing a list of objects.
On Sat, Aug 28, 2010 at 10:48 AM, cocolombo wrote: > Hello. > > I am putting objects (test) into a container object (tests) and the > test object is also a container for a another list of object > (scores). > > Problem is that all instances of class tests have the same value. > > To illustrate: > > class score(object): > val = 0 The previous line does nothing useful; delete it. > def __init__(self, val): > self.val = val > def __str__(self): > return str(self.val) + "\n" > > class test(object): > listOfScores = [] No! This makes the list a class/static variable *shared between all instances*. Delete the previous line and define a proper initializer: def __init__(self): self.listOfScores = [] > def __str__(self): > ret = "" > for s in self.listOfScores: > ret += str(s) > return ret > > class tests(object): > listOfTest = [] Again, same problem. def __init__(self): self.listOfTest = [] > def __str__(self): > ret = "" > for t in self.listOfTest: > ret += str(t) > return ret That is more efficiently+concisely written as: return "".join(str(t) for t in self.listOfTest) > Now I run the script > : > == > score1 = score(10) > score2 = score(20) > score3 = score(30) > score4 = score(40) > > test1 = test() > test2 = test() > > > test1.listOfScores.append(score1) > test1.listOfScores.append(score2) > test2.listOfScores.append(score3) > test2.listOfScores.append(score4) > > theTests = tests() > theTests.listOfTest.append(test1) > theTests.listOfTest.append(test2) > > print theTests.listOfTest[0] > print theTests.listOfTest[1] > > == > > This is the data structure I am EXPECTING: > But what I get is this: > What is wrong ? Python is not Java/C# and has no instance variable declarations. You just assign to an attribute of self in __init__ and *that* is what creates instance variables. Any variables you assign to directly in the class body (as you were doing with listOfScores and listOfTest) are made class variables (Java lingo: "static variables"), and are /shared between all instances/, which is rarely what one actually wants. To get regular instance variables, define a proper __init__() and assign the variables to self therein. Also, per PEP 8 (http://www.python.org/dev/peps/pep-0008/ ): - Classes are conventionally CapitalizedWords, so name your classes Score, Test, and Tests rather than score, test, and tests. - Variables/methods are conventionally underscored_between_words, so list_of_test rather than listOfTest. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Object containing a list of objects.
cocolombo wrote: > Problem is that all instances of class tests have the same value. > > To illustrate: > class tests(object): > listOfTest = [] This makes listOfTest a class attribute. To get one list per instance define it in the initializer: class Tests(object): def __init__(self): self.tests = [] Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Object containing a list of objects.
On 28/08/2010 18:48, cocolombo wrote: Hello. I am putting objects (test) into a container object (tests) and the test object is also a container for a another list of object (scores). Problem is that all instances of class tests have the same value. To illustrate: class score(object): val = 0 def __init__(self, val): self.val = val def __str__(self): return str(self.val) + "\n" class test(object): listOfScores = [] def __str__(self): ret = "" for s in self.listOfScores: ret += str(s) return ret class tests(object): listOfTest = [] def __str__(self): ret = "" for t in self.listOfTest: ret += str(t) return ret Now I run the script : == score1 = score(10) score2 = score(20) score3 = score(30) score4 = score(40) test1 = test() test2 = test() test1.listOfScores.append(score1) test1.listOfScores.append(score2) test2.listOfScores.append(score3) test2.listOfScores.append(score4) theTests = tests() theTests.listOfTest.append(test1) theTests.listOfTest.append(test2) print theTests.listOfTest[0] print theTests.listOfTest[1] == This is the data structure I am EXPECTING: theTests test1 ---score1=10 ---score2=20 test2 ---score3=30 ---score4=40 But what I get is this: theTests test1 ---score1=10 ---score2=20 ---score3=30 ---score4=40 test2 ---score1=10 ---score2=20 ---score3=30 ---score4=40 What is wrong ? When you write: class test(object): listOfScores = [] you're making 'listOfScores' an attribute of the class. If you want it to be an attribute of an instance you should write: class test(object): def __init__(self): self.listOfScores = [] -- http://mail.python.org/mailman/listinfo/python-list
Object containing a list of objects.
Hello. I am putting objects (test) into a container object (tests) and the test object is also a container for a another list of object (scores). Problem is that all instances of class tests have the same value. To illustrate: class score(object): val = 0 def __init__(self, val): self.val = val def __str__(self): return str(self.val) + "\n" class test(object): listOfScores = [] def __str__(self): ret = "" for s in self.listOfScores: ret += str(s) return ret class tests(object): listOfTest = [] def __str__(self): ret = "" for t in self.listOfTest: ret += str(t) return ret Now I run the script : == score1 = score(10) score2 = score(20) score3 = score(30) score4 = score(40) test1 = test() test2 = test() test1.listOfScores.append(score1) test1.listOfScores.append(score2) test2.listOfScores.append(score3) test2.listOfScores.append(score4) theTests = tests() theTests.listOfTest.append(test1) theTests.listOfTest.append(test2) print theTests.listOfTest[0] print theTests.listOfTest[1] == This is the data structure I am EXPECTING: theTests test1 ---score1=10 ---score2=20 test2 ---score3=30 ---score4=40 But what I get is this: theTests test1 ---score1=10 ---score2=20 ---score3=30 ---score4=40 test2 ---score1=10 ---score2=20 ---score3=30 ---score4=40 What is wrong ? Thanks -- http://mail.python.org/mailman/listinfo/python-list
Re: Tag parsing in python
On 08/28/10 11:14, agnibhu wrote:
For example say I've key words like abc: bcd: cde: like that... So the
user may use like
abc: How are you bcd: I'm fine cde: ok
So I've to extract the "How are you" and "I'm fine" and "ok"..and
assign them to abc:, bcd: and cde: respectively..
For this, you can do something like
>>> s = "abc: how are you bcd: I'm fine cde: ok"
>>> import re
>>> r = re.compile(r'(\w+):\s*((?:[^:](?!\w+:))*)')
>>> r.findall(s)
[('abc', 'how are you'), ('bcd', "I'm fine"), ('cde', 'ok')]
Yes, it's a bit of a gnarled regexp, but it seems to do the job.
There may be combination of keyowords introduced in future.
like abc: xy: How are you So new keywords qualifying the other
keywords so on.
I'm not sure I understand this bit of what you're asking. If you
have
s = "abc: xy: How are you"
why should that not be parsed as
>>> r.findall("abc: xy: How are you")
[('abc', ''), ('xy', 'How are you')]
as your initial description prescribes?
-tkc
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Functional composition in python
Hello all. Some time ago I wrote a little library:
http://github.com/si14/python-functional-composition/ , inspired by
modern functional languages like F#. In my opinion it is quite useful
now, but I would like to discuss it.
An example of usage:
import os
from pyfuncomp import composable, c, _
def comment_cutter(s):
t = s.find("#")
return s if t < 0 else s[0:t].strip()
@composable #one can use a decorator to make a composable function
def empty_tester(x):
return len(x) > 0 and x[0] != "#"
path_prefix = "test"
config_parser = (c(open) >> #or use a transformer function
c(str.strip).map >> #"map" acts like a function modifier
c(comment_cutter).map >>
empty_tester.filter >> #so does "filter"
c(os.path.join)[path_prefix, _].map) #f[a, _, b] is
used to make a partial.
#f[a, foo:bar,
baz:_] is also correct
print config_parser("test.txt")
print (c("[x ** %s for x in %s]")[2, _] << c(lambda x: x * 2).map)([1, 2, 3])
Any suggestions are appreciated.
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Tag parsing in python
Hi all, I'm a newbie in python. I'm trying to create a library for parsing certain keywords. For example say I've key words like abc: bcd: cde: like that... So the user may use like abc: How are you bcd: I'm fine cde: ok So I've to extract the "How are you" and "I'm fine" and "ok"..and assign them to abc:, bcd: and cde: respectively.. There may be combination of keyowords introduced in future. like abc: xy: How are you So new keywords qualifying the other keywords so on.. So I would like to know the python way of doing this. Is there any library already existing for making my work easier. ? ~ Agnibhu -- http://mail.python.org/mailman/listinfo/python-list
Re: rouble importing cx_Oracle on HPUX
Hello, On Sat, Aug 28, 2010 at 09:27:05AM -0400, Cliff Martin wrote: > Yes, our entire toolchain is 64 bit - a mix of > stuff I have downloaded and built and some > packages from HP (in the form of depot files) > GCC was downloaded from HP, for example. I see. I bootstrapped from bundled cc, hence all the problems. > Python -d did not generate any additional > information, and so was not helpful (should this > work?). Oops I was wrong about the python -d -- correct option is -v of course... > Python -v did, however, and it came up with a > number of unresolved symbols all seeming to be > from libnnz11.so. I tried linking against all of > the *.so files in ORACLE_HOME/lib, but I don't > remember trying libttsh11 specifically. I will > try it again on Monday. You're using Oracle 11 vs our v10 (we also have v8, v9 and v11 in production, but not on this HP-UX server), but I think the problem with the libnnz is the same: Oracle doesn't put correct shared library dependencies into the libnnzXX.so dynamic section header (it should list libttshXX.so as NEEDED but apperently doesn't). Probably their distribution for Solaris is better, I didn't check (I'll ask our DBAs on Monday). -- With best regards, xrgtn -- http://mail.python.org/mailman/listinfo/python-list
love me
1st step add me in like box on my facbook page at this link http://www.facebook.com/pages/loveme/145529285481739 2nd step visit this link http://www.kqzyfj.com/click-3778203-10786395 -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On 28/08/2010 14:41, Peter Otten wrote: BTW, I didn't expect it but I get different results on different runs. Clever code. I will give it a go soonest. Elec off for the next 24 hours in my neck of the woods. Urgh. Python can't "import electricity" just yet :) \d -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
On Sat, 28 Aug 2010 09:48:47 +0100 Ian wrote: > > def palindromep(s): > > def reversed(s): > > return s[::-1] > > return s == reversed(s) > I like this. > > s[::-1] is obscure and non-obvious, especially to Python noobs. > > This makes it clear what is going on and why at a cost of very little code. It seems unnecessary to me. Even if you can't figure it out through simple inspection, it takes seconds to fire up Python and type "print 'abc'[::-1]" into it to see what that does. Then you have another tool in your toolbox. -- D'Arcy J.M. Cain | Democracy is three wolves http://www.druid.net/darcy/| and a sheep voting on +1 416 425 1212 (DoD#0082)(eNTP) | what's for dinner. -- http://mail.python.org/mailman/listinfo/python-list
Re: Trouble importing cx_Oracle on HPUX
Hi, thank you for getting back to me. Yes, our entire toolchain is 64 bit - a mix of stuff I have downloaded and built and some packages from HP (in the form of depot files) GCC was downloaded from HP, for example. I had to manually add -mlp64 to the CC and CXX lines in the Python Makefile to get it to build 64 bit Python 3. I also had to define PATH_MAX in about 5 files, because it was not resolving it, and it was just easier to add it than to spend more time trying to make it work. I hate HP-UX, BTW. Python -d did not generate any additional information, and so was not helpful (should this work?). Python -v did, however, and it came up with a number of unresolved symbols all seeming to be from libnnz11.so. I tried linking against all of the *.so files in ORACLE_HOME/lib, but I don't remember trying libttsh11 specifically. I will try it again on Monday. -- Cliff On Sat, Aug 28, 2010 at 9:11 AM, Alexander Gattin wrote: > Hello, > > On Thu, Aug 26, 2010 at 08:08:42PM -0700, Cliff > Martin wrote: > > I have just gotten done building Python 3.1.2 on > > HPUX 11.31 Itanium (IA64) using gcc 4.4.3, and > > have tried building cx_Oracle to go with it. The > > build succeeds, but test and importing does not. > > I have tried building Python with threads and > > without. The only exotic thing I do with the > > configure for python is to supply -mlp64, which > > BTW, did you build all GNU toolchain in 64 bit > mode? I made some tries to get 64bit python etc > but stubmled over compilation errors and didn't > get enough free time to finish the effort. > > > makes it a 64 bit build. Python 3 appears to > > work just fine, and cx_Oracle has worked on this > > same architecture in the past with Python 2.6.5. > > did you try to start python -d and > >>> import cx_Oracle? > > It may reveal that some symbols in libnnz10 aren't > resolvable. If this is the case, try linking with > bith libttsh10 and libnnz10: > > .../cx_Oracle-x.y.z $ LDFLAGS="-lttsh10" python setup.py install > > Alternatively, try linking against "static" > version of libclntsh10 -- libclntst10. > > -- > With best regards, > xrgtn > -- http://mail.python.org/mailman/listinfo/python-list
Re: Trouble importing cx_Oracle on HPUX
Hello, On Thu, Aug 26, 2010 at 08:08:42PM -0700, Cliff Martin wrote: > I have just gotten done building Python 3.1.2 on > HPUX 11.31 Itanium (IA64) using gcc 4.4.3, and > have tried building cx_Oracle to go with it. The > build succeeds, but test and importing does not. > I have tried building Python with threads and > without. The only exotic thing I do with the > configure for python is to supply -mlp64, which BTW, did you build all GNU toolchain in 64 bit mode? I made some tries to get 64bit python etc but stubmled over compilation errors and didn't get enough free time to finish the effort. > makes it a 64 bit build. Python 3 appears to > work just fine, and cx_Oracle has worked on this > same architecture in the past with Python 2.6.5. did you try to start python -d and >>> import cx_Oracle? It may reveal that some symbols in libnnz10 aren't resolvable. If this is the case, try linking with bith libttsh10 and libnnz10: .../cx_Oracle-x.y.z $ LDFLAGS="-lttsh10" python setup.py install Alternatively, try linking against "static" version of libclntsh10 -- libclntst10. -- With best regards, xrgtn -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
On Aug 28, 11:55 am, Steven D'Aprano wrote:
> On Sat, 28 Aug 2010 09:22:13 +0300, Jussi Piitulainen wrote:
> > Terry Reedy writes:
> >> On 8/27/2010 3:43 PM, Jussi Piitulainen wrote:
> >> > Dave Angel writes:
[snip]
> Not everything needs to be a built-in method. There is already a standard
> way to spell "reverse a string":
>
> astring[::-1]
>
> If you don't like that, you can do this:
>
> ''.join(reversed(astring))
I've had to debug code that assumed str(reversed('abc')) == 'cba'
>>> str(reversed('abc'))
''
So, a str doesn't "construct" like tuple/list...it's a call to
__str__().
It's designated as a "friendly print out" (that's my phrasing).
>>> list('abc')
['a', 'b', 'c']
I s'pose str is special (2.6) in some way, but it doesn't parallel the
other builtins.
[Not at Terry / Steve intended -- just most relevant post to respond
to]
Jon.
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Re: Queue cleanup
In article <4c78e7a5$0$28655$c3e8...@news.astraweb.com>, Steven D'Aprano wrote: > >On the other hand, the reason that CPython still has reference counting >is that the alternatives tried so far are unacceptably for non-threaded >code. No, it's *a* reason, the other main reason being that refcounting is much easier for a random C library. -- Aahz (a...@pythoncraft.com) <*> http://www.pythoncraft.com/ "...if I were on life-support, I'd rather have it run by a Gameboy than a Windows box." --Cliff Wells -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
donn wrote:
> On 28/08/2010 12:03, Peter Otten wrote:
>> But be warned that if you set the limit too high instead of giving you a
>> RuntimeError your program will segfault.
> Silly question: is there any way to tell the future in this case? I
> mean, ask for X recursion limit, and catch an error (or something) if
> that won't fly.
I don't think it's a silly question, and I don't think there is an exact
answer, even for a given platform. You'll want to stay well below the
number calculated by the following script:
import os
import subprocess
SCRIPT = "tmp_check.py"
def ok(n):
return subprocess.call(["python", SCRIPT, str(n)]) == 0
if __name__ == "__main__":
if not os.path.exists(SCRIPT):
with open(SCRIPT, "w") as out:
out.write("""\
import sys
def f():
return f()
if __name__ == "__main__":
n = int(sys.argv[1])
sys.setrecursionlimit(n)
try:
f()
except RuntimeError:
pass
""")
low = 1000
while True:
new_low = 2*low
if not ok(new_low):
high = new_low
break
low = new_low
while high - low > 1:
mid = (low + high) // 2
if ok(mid):
low = mid
else:
high = mid
print "max recursion limit", low, high
BTW, I didn't expect it but I get different results on different runs.
Peter
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Re: Queue cleanup
In article <4c78572c$0$28655$c3e8...@news.astraweb.com>, Steven D'Aprano wrote: >On Fri, 27 Aug 2010 09:16:52 -0700, Aahz wrote: >> In article , MRAB >> wrote: >>> >>>An object will be available for garbage collection when nothing refers >>>to it either directly or indirectly. If it's unreferenced then it will >>>go away. >> >> This isn't actually garbage collection as most people think of it. >> Refcounting semantics mean that objects get reaped as soon as nothing >> points at them. OTOH, CPython does also have garbage collection to back >> up refcounting so that when you have unreferenced object cycles they >> don't stay around. > >I've repeatedly asked, both here and elsewhere, why reference counting >isn't "real" garbage collection. Nobody has been able to give me a >satisfactory answer. As far as I can tell, it's a bit of pretentiousness >with no basis in objective fact. You'll notice that I was very careful to qualify my statement with "as most people think of it". Also, because CPython has two different memory management mechanisms, refcounting and cycle detection, and the module that controls cycle detection is called "gc", I think it's simpler to follow along with the Python docs -- and critically important to remind people that there are in fact two different systems. -- Aahz (a...@pythoncraft.com) <*> http://www.pythoncraft.com/ "...if I were on life-support, I'd rather have it run by a Gameboy than a Windows box." --Cliff Wells -- http://mail.python.org/mailman/listinfo/python-list
Re: GSM to ISO / UCS2 to ISO
Hello, On Mon, Aug 16, 2010 at 08:01:36PM +1000, James Mills wrote: > In an effort to avoid re-inventing the wheel so to speak > I was wondering if anyone's come across libraries/tools, etc > that achieve the same kind of functionality as the tools > library in this java app. unfortunately, no (except some Perl implementations). I'd suggest to add GSM0338 module to standard GNU libc's iconv: /usr/lib/gconv/GSM0338.so /usr/lib/gconv/gconv-modules Probably I'm wrong, but this way it'd become readily available to all programs using iconv(3), including python. > http://code.google.com/p/ipddump/source/browse/trunk/src/ipddump/tools/Gsm2Iso.java I'm Amazed (c) Pixies. This Java code really sucks. -- With best regards, xrgtn -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Paul Rubin writes: > Ian writes: > > On 27/08/2010 21:51, Jussi Piitulainen wrote: > >> Meanwhile, I have decided to prefer this: > >> > >> def palindromep(s): > >> def reversed(s): > >> return s[::-1] > >> return s == reversed(s) > > I like this. > > s[::-1] is obscure and non-obvious, especially to Python noobs. > > Overriding the 'reversed' builtin even in an inner scope is a little > bit ugly. > > If you don't mind some overhead, list(s)==list(reversed(s)) (using > the built-in reversed, not the special obscure one) is pretty clear. Thanks for that. I'm beginning to like it - not its overhead but certainly its natural clarity. It wins over ''.join(reversed(s)) easily, in my eyes. -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Arnaud Delobelle writes: > Also, I an not aware that it is customary in python to name > predicate functions with a "p" suffix - Python is not Lisp! Just to clarify my position: I did not mean to imply that names like palindromep might be customary in Python - clearly they are not - and I am quite aware that Python is not Lisp. My background is elsewhere, I was not paying particular attention to the name at all, and I just could not be bothered to look up what implications any of palindrome, palindromic, ispalindrome, is_palindrome, isPalindrome, has_palindrome_nature, check_palindrome and so on might have in Python. Perhaps I should have used a neutral name like f or test or so, but it did not occur to me at the time. -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Steven D'Aprano writes: > On Sat, 28 Aug 2010 09:22:13 +0300, Jussi Piitulainen wrote: >> Terry Reedy writes: >>> On 8/27/2010 3:43 PM, Jussi Piitulainen wrote: >>> > Dave Angel writes: >>> >>> > There could easily be a .reverse() method on strings. It would return >>> > the reversed string, like .swapcase() returns the swapcased string. >>> >>> Could be, but the main use case seems to be for palindrome testing ;-) >>> Given that slicing and reversed() can do the same thing, the need is >>> thin. >> >> The need is quite thin, but immutability of strings is not an issue, >> just like there can be .swapcase() though strings are immutable. That is >> all I am saying above. > > You're right, there could be a reversed() method for strings. There > could also be a disemvowel method that removes vowels, a randomise > method that shuffles the letters around, a studlycaps method that > changes the case of each letter randomly, and a method to check that > brackets () are well- formed. They would all be useful to > somebody. There are lots of different methods that strings could > have. Where do you draw the line? When I said that there could be such a method, I was merely objecting to a statement, made in response to me, that there could not be such a method because strings are immutable. You clearly agree with me that that statement was not correct. Would you have let it stand if it was made to you? To answer your question, I don't see a real need for .reversed() in strings, but I do think .reversed() would be much more useful than .swapcase() which is in Python now and for which I see no use at all. I have not proposed adding anything to Python. I have only asked if there is any nicer expression for string reversal than [::-1] in Python now, and corrected an incorrect statement that was made in response to me that there could not be a string reversal method because Python strings are immutable. I am still not proposing that anything be added to Python. I have not even criticized Python for not having a nicer expression for string reversal than [::-1]. I have merely asked if there is one, because I didn't know if there is one, and I have shown some snippets of code to illustrate what I might mean by nicer. Someone even understood me. (Thanks.) I think I have received the answer to my question by now - that there is no obviously nicer way, and all other string reversal expressions require some extra cruft and overhead. > Not everything needs to be a built-in method. There is already a > standard way to spell "reverse a string": > > astring[::-1] > > If you don't like that, you can do this: > > ''.join(reversed(astring)) I know. I agree. I was also shown a different way to test for palindromicity, list(s) == list(reversed(s)) which is quite nice apart from the overhead. > I don't object to a hypothetical reverse() method on strings, but > the gain is minimal. I have not suggested that such a method should be added to the language. I merely corrected a statement that there could not be such a method because strings are immutable. I would not have bothered to do even that if that incorrect statement had not been made in response to my own post. I agree that the gain would be minimal. There is no harm in the method either, so I would not object to it if somebody were to propose its addition, but just to clarify my position: I have not proposed it. Hope this helps. -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On 28/08/2010 12:03, Peter Otten wrote: But be warned that if you set the limit too high instead of giving you a RuntimeError your program will segfault. Silly question: is there any way to tell the future in this case? I mean, ask for X recursion limit, and catch an error (or something) if that won't fly. \d -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On 28/08/2010 11:17, Carl Banks wrote: It's simple. Copy the object to flatten onto your stack. Pop one item off the stack. If the item you popped is a list, push each item of that list onto the stack. Otherwise yield the value. Loop until stack is empty. Nice. The reversed thing was throwing me, but I think it's so that what comes first in a list will thus come first (on the end) of the stack. So I'm not suggesting that recursion be avoided (I've probably written a dozen recursive functions in the last week), I'm just saying sometimes it makes sense to use iteration even for problems recursion is tailor-made for. Thanks for that. In parsing the XML (using lxml) I actually did my own stack thing with while loops, to build the entire Tag object 'tree' — just because I wanted to see how to do it sans recursion. I still get cold shakes when I scroll past that monster! On the subject of recursion, and looking at my OP object model: the Tag objects that model the tags in an SVG file; how would I 'walk' the object tree without employing recursion? I am stuck on the eventual need to call child.flatwalk() and bang! there's recursion. I get the sense that it would be an external walk() function that does some stackery-trickery and reuturns/yields the tree/branch — all divorced from the actual objects. So, no flatwalk() methods needed at all. This kind of bothers me because it's nice to have objects 'know' what to do and addressing their siblings and children seems a vital part of that. Look at the case of asking a Tag for its XML source: Say g is a G() instance: print g.get_xml(), would have to do some string churning (specific to a g tag) and then start walking its children and ask them to do specific string stuff (in their contexts). This means I have short methods in each Tag instance that "know" how to represent themselves as XML and they can return that value. If I divorce the thing, it becomes a large loop with a lot of switchy-ifs to engage various blocks of string-fu. I hope that made sense. I can post my code if that would help. \d -- http://mail.python.org/mailman/listinfo/python-list
Re: How to convert (unicode) text to image?
kj writes:
> Thanks for the pointer, but...
>
>
> The documentation I have found for PIL (at
> http://www.pythonware.com/library/pil/handbook) is beyond atrocious.
> If this is the only way to learn how to use this library, then I
> really don't understand how anyone who is not clairvoyant can do it.
>
> Example: I went to the docs page for ImageDraw. There I find that
> the constructor for an ImageDraw.Draw object takes an argument,
> but *what* this argument should be (integer? object? string?) is
> left entirely undefined. From the examples given I *guessed* that
> it was an object of class Image, so I repeated the exercise: I
> consulted the docs for the Image module. There I learn that the
> constructor for the Image class takes among its parameters one
> called "mode" and one called "color", but, here again, what these
> parameters are is left completely undefined. ("mode" is left both
> syntactically and semantically undefined; "color" is left syntactically
> undefined, though the documentation includes a bit by way of semantic
> definition of this parameter.)
The first time you read the PIL docs, read the introduction. After that
I find the docs pretty easy to use, even though it is true that it is
quite terse.
E.g. for the mode, look at the "concepts" page in the intro:
http://www.pythonware.com/library/pil/handbook/concepts.htm
> What's up with this practice of leaving parameters undefined like
> this??? Wasn't it obvious to the person writing the Image module
> docs that without explaining what these parameters should be the
> documentation is nearly useless? Is such poor documentation an
> unintended consequence of "duck typing"???
>
> Sorry for the outburst, but unfortunately, PIL is not alone in
> this. Python is awash in poor documentation.
>
> The number two complaint I've heard from those who dislike Python
> is the poor quality of its documentation, and in particular the
> fact that function parameters are typically left undefined, as is
> the case in the PIL docs. I like Python a lot, but I have to agree
> with this criticism. (The number one complaint has to do with the
> syntactic significance of whitespace; of course, I find *this*
> criticism silly.)
>
> What is most frustrating about such poor documentation is that it
> is exactly the opposite from what one would expect from the
> carefulness and thoroughness found in the PEPs...
I find the Python docs very good on the whole.
> I have been using Python as my primary scripting language for about
> one year, after many years of programming in Perl, and now Python
> is my language of choice. But I must say that the documentation
> standards I found in the Perl world are *well above* those in the
> Python world. This is not to say that Perl documentation is always
> excellent; it certainly has its gaps, as one would expect from
> volunteer-contributed software. But I don't recall being frustrated
> by Perl module docs anywhere nearly as often as I am by Python
> module docs. I have to conclude that the problem with Python docs
> is somehow "systemic"...
I have never programmed in Perl (although I have needed to read some
Perl) but over the years I have used C, C++, lisp variants, PHP, Ruby, Caml
variants, Haskell, Javascript (and others before the era of the
web). I don't find that Python online docs on the web are worse than
online docs for any of those languages.
--
Arnaud
--
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Re: Queue cleanup
On Fri, 27 Aug 2010 18:06:19 -0700, Paul Rubin wrote: > Steven D'Aprano writes: >> I've repeatedly asked, both here and elsewhere, why reference counting >> isn't "real" garbage collection. Nobody has been able to give me a >> satisfactory answer. As far as I can tell, it's a bit of >> pretentiousness with no basis in objective fact. > > Well, it's a bit of a subjective matter. I'd say it's not real gc > because 1) it's unsound (misses reference cycles), You can add cycle detection to a reference count gc, at the cost of more complexity. If you read the Wikipedia article I linked to, tracing algorithms can also be unsound: Some collectors running in a particular environment can correctly identify all pointers (references) in an object; these are called "precise" (also "exact" or "accurate") collectors, the opposite being a "conservative" or "partly conservative" collector. Conservative collectors have to assume that any bit pattern in memory could be a pointer if (when interpreted as a pointer) it would point into any allocated object. Thus, conservative collectors may have some false negatives, where storage is not released because of accidental fake pointers... http://en.wikipedia.org/wiki/Garbage_collection_(computer_science) > and 2) it requires > constant attention from the mutator to incr and decr the reference > counts. Yes. And? > So developing modules for the CPython API means endlessly > finding and fixing refcount bugs that lead to either crashes/security > failures, or memory leaks. If you program the Java JNI or a typical > Lisp FFI, you'll find that real gc is a lot simpler to use since you > avoid all the refcount maintenance hassles. You allocate memory and > shut your eyes, and the gc takes care of freeing it when it figures out > that you are done. Refcounting is basically a form of manual memory > management, while gc is automatic. That's a problem with the CPython API, not reference counting. The problem is that the CPython API is written at too low a level, beneath that at which the garbage collector exists, so naturally you have to manually manage memory. > Someone said here recently that as a program gets larger, saying "this > will work as long as we do X every time without fail" becomes equal to > saying "this won't work". Substitute "properly maintain all ref counts" > for X and you can see the problem. I've seen released "production" > "tested" Python C modules with subtle refcount bugs on more than one > occasion. In gc'd systems there are fewer places for the code to go > wrong. On the other hand, tracing gcs have their own set of problems too, mostly due to the use of finalizers and attempts to make garbage collection run more predictably. See here: http://publib.boulder.ibm.com/infocenter/javasdk/v1r4m2/topic/com.ibm.java.doc.diagnostics.142j9/html/coexistwithgc.html Quote: For tidying Java resources, think about the use of a clean up routine. When you have finished with an object, call the routine to null out all references, deregister listeners, clear out hash tables, and so on. This is far more efficient than using a finalizer and has the useful side-benefit of speeding up garbage collection. The Garbage Collector does not have so many object references to chase in the next garbage collection cycle. Translated: "Rather than relying on the garbage collector to clean up resources after you, do it yourself, manually, so the garbage collector has less work to do." Tracing garbage collectors aren't a panacea. They're software themselves, and complex software, which means they're subject to bugs like the one which plagued Flash plugin 9: http://gskinner.com/blog/archives/2008/04/failure_to_unlo.html The more complicated the garbage collector, the more scope you have for some interaction between your high-level code and the gc leading to memory not be reclaimed or extreme slowdown. Like this: http://tech.puredanger.com/2009/02/11/linkedblockingqueue-garbagecollection/ -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: ftplib limitations?
In message <4c78cc0d.8050...@sschwarzer.net>, Stefan Schwarzer wrote: > In message , Lawrence D'Oliveiro wrote: >> >> It might not be the fault of the FTP server. If you’re going through a >> router doing NAT, that could be where the timeout is happening. > > Good point, thanks! That may explain why it's a low-level > socket error instead of a 4xx timeout message from the > server which I would have expected. The reason why I thought of it was because it kept happening to me back when I was using a D-Link DSL-500 to provide my ADSL connection. Unfortunately... > If it's the router, the OP might try to change their router > settings to get rid of the problem. ... if they’re using a typical consumer ADSL router box like the above, they may not have any NAT table timeout settings to play with to cure the problem. I certainly couldn’t find any in mine. In my case, I solved the problem by using a Linux box as my router. -- http://mail.python.org/mailman/listinfo/python-list
Simple hack to get $5000 to your *Paypal account
Simple hack to get $5000 to your *Paypal account At http://ucanget.co.cc i have hidden the Paypal Form link in an image. in that website on Right Side below search box, click on image and enter your name and Paypal ID. -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
On Sat, 28 Aug 2010 09:22:13 +0300, Jussi Piitulainen wrote: > Terry Reedy writes: >> On 8/27/2010 3:43 PM, Jussi Piitulainen wrote: >> > Dave Angel writes: >> >> > There could easily be a .reverse() method on strings. It would return >> > the reversed string, like .swapcase() returns the swapcased string. >> >> Could be, but the main use case seems to be for palindrome testing ;-) >> Given that slicing and reversed() can do the same thing, the need is >> thin. > > The need is quite thin, but immutability of strings is not an issue, > just like there can be .swapcase() though strings are immutable. That is > all I am saying above. You're right, there could be a reversed() method for strings. There could also be a disemvowel method that removes vowels, a randomise method that shuffles the letters around, a studlycaps method that changes the case of each letter randomly, and a method to check that brackets () are well- formed. They would all be useful to somebody. There are lots of different methods that strings could have. Where do you draw the line? Not everything needs to be a built-in method. There is already a standard way to spell "reverse a string": astring[::-1] If you don't like that, you can do this: ''.join(reversed(astring)) I don't object to a hypothetical reverse() method on strings, but the gain is minimal. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: How to convert (unicode) text to image?
In Benjamin Kaplan
writes:
>On Fri, Aug 27, 2010 at 8:01 PM, kj wrote:
>>
>>
>> Hi! =A0Does anyone know of an easy way to convert a Unicode string into a=
>n image file (either jpg or png)?
>>
>Do you mean you have some text and you want an image containing that
>text? PIL's ImageDraw module can do that.
Thanks for the pointer, but...
The documentation I have found for PIL (at
http://www.pythonware.com/library/pil/handbook) is beyond atrocious.
If this is the only way to learn how to use this library, then I
really don't understand how anyone who is not clairvoyant can do it.
Example: I went to the docs page for ImageDraw. There I find that
the constructor for an ImageDraw.Draw object takes an argument,
but *what* this argument should be (integer? object? string?) is
left entirely undefined. From the examples given I *guessed* that
it was an object of class Image, so I repeated the exercise: I
consulted the docs for the Image module. There I learn that the
constructor for the Image class takes among its parameters one
called "mode" and one called "color", but, here again, what these
parameters are is left completely undefined. ("mode" is left both
syntactically and semantically undefined; "color" is left syntactically
undefined, though the documentation includes a bit by way of semantic
definition of this parameter.)
What's up with this practice of leaving parameters undefined like
this??? Wasn't it obvious to the person writing the Image module
docs that without explaining what these parameters should be the
documentation is nearly useless? Is such poor documentation an
unintended consequence of "duck typing"???
Sorry for the outburst, but unfortunately, PIL is not alone in
this. Python is awash in poor documentation.
The number two complaint I've heard from those who dislike Python
is the poor quality of its documentation, and in particular the
fact that function parameters are typically left undefined, as is
the case in the PIL docs. I like Python a lot, but I have to agree
with this criticism. (The number one complaint has to do with the
syntactic significance of whitespace; of course, I find *this*
criticism silly.)
What is most frustrating about such poor documentation is that it
is exactly the opposite from what one would expect from the
carefulness and thoroughness found in the PEPs...
I have been using Python as my primary scripting language for about
one year, after many years of programming in Perl, and now Python
is my language of choice. But I must say that the documentation
standards I found in the Perl world are *well above* those in the
Python world. This is not to say that Perl documentation is always
excellent; it certainly has its gaps, as one would expect from
volunteer-contributed software. But I don't recall being frustrated
by Perl module docs anywhere nearly as often as I am by Python
module docs. I have to conclude that the problem with Python docs
is somehow "systemic"...
--
http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
On Sat, 28 Aug 2010 09:48:47 +0100, Ian wrote: > On 27/08/2010 21:51, Jussi Piitulainen wrote: >> Meanwhile, I have decided to prefer this: >> >> def palindromep(s): >> def reversed(s): >> return s[::-1] >> return s == reversed(s) > I like this. It's silly, needlessly complicated, and inefficient. Why create a *one line* nested function that only gets called once? Every single time you call the function, it has to create the inner function again, then call it once, then throw it away. Admittedly Python does recreate the inner function from pre-compiled parts, which is quick, but still, it doesn't gain you anything that a simple comment wouldn't give: def palindromep(s): return s == s[::-1] # Compare s to its reverse. > s[::-1] is obscure and non-obvious, especially to Python noobs. *Only* to Python noobs. Slicing is fundamental to Python, and using a slice of [::-1] to reverse something is a basic Python idiom. > This makes it clear what is going on and why at a cost of very little > code. > > Very helpful to the maintenance programming in 18 months time! Only if writing three lines when one would do is your definition of "helpful". -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Queue cleanup
On Sat, 28 Aug 2010 00:33:10 -0700, Paul Rubin wrote: > Dennis Lee Bieber writes: >> The nice thing about it [reference counting] is that it is sort >> of deterministic -- one can examine code and determine that an object >> is collected at some point in the execution... >> Heap marking, OTOH, tends to run at indeterminate times, which could >> have an impact if one needs predictable response timings > > Reference counting has the same problem. In theory, yes, but in practice ref counting tends to spread out the performance impact more smoothly. There are exceptions, such as the one you mention below, but as a general rule ref counting isn't subject to the "embarrassing pauses" that tracing garbage collectors tend to be subject to. > If you drop the last reference > to a complex structure, it could take quite a long time to free all the > components. By contrast there are provably real-time tracing gc > schemes, including some parallelizeable ones. I could be wrong, but how can they not be subject to the same performance issue? If you have twenty thousand components that all have to be freed, they all have to be freed whether you do it when the last reference is cleared, or six seconds later when the gc does a sweep. > One reason CPython still > can't run threads on parallel cores is it would have to lock the > reference counts every time they're updated, and the slowdown from that > is terrible. On the other hand, the reason that CPython still has reference counting is that the alternatives tried so far are unacceptably for non-threaded code. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On Aug 28, 3:03 am, Peter Otten <__pete...@web.de> wrote: > donn wrote: > > On 28/08/2010 08:43, Peter Otten wrote: > >> If you call functions within functions (or methods, it doesn't matter) > >> they consume stack space > > > Right, got it. Darn, but at least there's that setrecursionlimit call. > > But be warned that if you set the limit too high instead of giving you a > RuntimeError your program will segfault. Ah, an advantage of iteration I forgot: no recursion limits or stack overflows. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
donn wrote: > On 28/08/2010 08:43, Peter Otten wrote: >> If you call functions within functions (or methods, it doesn't matter) >> they consume stack space > > Right, got it. Darn, but at least there's that setrecursionlimit call. But be warned that if you set the limit too high instead of giving you a RuntimeError your program will segfault. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Paul Rubin writes: > Ian writes: >> On 27/08/2010 21:51, Jussi Piitulainen wrote: >>> Meanwhile, I have decided to prefer this: >>> >>> def palindromep(s): >>> def reversed(s): >>> return s[::-1] >>> return s == reversed(s) >> I like this. >> s[::-1] is obscure and non-obvious, especially to Python noobs. It may be non-obvious to newcomers, but it is quite a well known idiom. Also, I an not aware that it is customary in python to name predicate functions with a "p" suffix - Python is not Lisp! > > Overriding the 'reversed' builtin even in an inner scope is a little bit > ugly. I agree. > If you don't mind some overhead, list(s)==list(reversed(s)) (using the > built-in reversed, not the special obscure one) is pretty clear. May I suggest a comment instead: def ispalindrome(s): # s[::-1] evaluates to the string s reversed return s == s[::-1] -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: rfile.readline()
sarah wrote:
i want to know that what this function returns???
and what does this function do??
rfile.readline()
No way to tell what the function returns from your subject line.
As for what calling it does, that depends entirely on the object rfile.
If it's an instance of a class you wrote, you'll have to look up in your
source code. If it's an instance of one of the built-in system types,
or of a class in the standard library, then you can tell by looking up
that type.
I see standard classes bz2.BZ2File, codecs.StreamReader,
distutils.text_file, file, imaplib, mmap, io.IOBase, io.TextIOBase, and
multifile. These were from the docs for Python 2.6.
Most of these are probably analogous to file, in which case I can elaborate.
If rfile is an instance of file, perhaps by doing
rfile = open("myfile.txt", "r")
then rfile.readline() reads one line from that file, starting at the
current position, and leaves the file position after that line.
readline() stops when it reaches a newline (which it may convert,
depending on the setting of 'rb' versus 'r'), or when it reaches end of
file. The trailing newline (if any) is included in the returned string.
That string may be in byte form (Python 2.x), or in unicode (Python
3.x). In the latter case, it has been decoded according to parameters
of the particular open file.
DaveA
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Re: palindrome iteration
Ian writes: > On 27/08/2010 21:51, Jussi Piitulainen wrote: >> Meanwhile, I have decided to prefer this: >> >> def palindromep(s): >> def reversed(s): >> return s[::-1] >> return s == reversed(s) > I like this. > s[::-1] is obscure and non-obvious, especially to Python noobs. Overriding the 'reversed' builtin even in an inner scope is a little bit ugly. If you don't mind some overhead, list(s)==list(reversed(s)) (using the built-in reversed, not the special obscure one) is pretty clear. -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On Aug 27, 8:21 pm, donn wrote: > Each Tag has a flatwalk() method. The return from that is a list which > can be deeply nested. As an example, something like this: > L=[1, [2, 3, [4, [5, 6], 7], 8], [9, 10] ] > > (The numbers in the example would actually be Tag Instances.) > > Aim 1 > --- > I'm trying to write a generator around such lists so that I can 'walk' them: > > for parent, child in mystery_generator(L): > print level, item > > Right now, I am running a 'flatten' function on the entire list (which I > don't savvy, I found it online) and then I iterate over that flattened > list. This doesn't feel right to me. (Code at end.) Hmm. In the past I've argued that iterative techniques are superior to recursive approaches in terms of readability, understandability, and conciseness, and thus Python made the right decision to stress iteration over the Lisp/functional preference for recursion. I did consider recursion to be superior to operate on branched structures like trees. However, lately I've started thinking it's better to use iterative techniques even for situations like that. I say that as someone with no problem getting my head around recursion. Even if you disagree, I think there's value in learning iterative approaches to nested problems, in the same way that there's value to learning recursive approaches to linear problems. So here it is: def flatten_iter(s): stack = list() stack.extend(reversed(s)) while stack: item = stack.pop() if isinstance(item,list): stack.extend(reversed(item)) else: yield item It's simple. Copy the object to flatten onto your stack. Pop one item off the stack. If the item you popped is a list, push each item of that list onto the stack. Otherwise yield the value. Loop until stack is empty. There's many advantages to iterative approaches: 1. Less function call overhead (in time and space, I'd think) 2. Opportunity to optimize by scanning through the stack, something you can't do *at all* with recursion 3. Might be able to avoid things like passing around a namespace 4. Iteration is more readable, understandable, and concise in general (though I'd expect recursion is more refactorable than iteration so as the system grows the refactorability of recursion will start to outweigh other factors) The main advantage of recursion is if you have baggage associated with processing a node which does needed to be passed around. In the iterative approach that state has to be stored on the stack. So in those cases recursion is better. So I'm not suggesting that recursion be avoided (I've probably written a dozen recursive functions in the last week), I'm just saying sometimes it makes sense to use iteration even for problems recursion is tailor-made for. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: How to convert (unicode) text to image?
kj wrote: Hi! Does anyone know of an easy way to convert a Unicode string into an image file (either jpg or png)? TIA! ~k The question has no meaning as presently worded. If you have Unicode text that you need to render, so that you end up with an image of the text, as printed in some particular font and style, you'd probably start with PIL. Or perhaps one of the gui packages, like tkinter, wxpython, etc. If you have Unicode that was produced by trying to decode some jpeg image, then back up and don't do that. See the recent thread called "Writing byte stream as jpeg format to disk". The OP there had run a unicode decode on a byte stream that represented a jpeg file, and then tried to encode it again to get the jpeg data. Bad idea. If you have Unicode that specifies a file path that refers to a jpeg file, then you need to open the file, in "rb" mode, and copy it. If you have Unicode that gives the name of a person, and you want a portrait of that person, you need to call a photographer() function. The last one was a weak attempt at humor. DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
On 27/08/2010 21:51, Jussi Piitulainen wrote: Meanwhile, I have decided to prefer this: def palindromep(s): def reversed(s): return s[::-1] return s == reversed(s) I like this. s[::-1] is obscure and non-obvious, especially to Python noobs. This makes it clear what is going on and why at a cost of very little code. Very helpful to the maintenance programming in 18 months time! Regards Ian -- http://mail.python.org/mailman/listinfo/python-list
Re: ftplib limitations?
Hi Lawrence, On 2010-08-28 01:49, Lawrence D'Oliveiro wrote: >> Now it may be that the data connection, after having started >> the transfer, works as it should, but the control connection >> times out because the duration of the transfer is too long. > > It might not be the fault of the FTP server. If you’re going through a > router doing NAT, that could be where the timeout is happening. Good point, thanks! That may explain why it's a low-level socket error instead of a 4xx timeout message from the server which I would have expected. If it's the router, the OP might try to change their router settings to get rid of the problem. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On 28/08/2010 09:21, Arnaud Delobelle wrote: This flattens the list in the flatwalk method (which IMHO it should do given its name!): Heh, I often name things ahead of my actual capacity to implement them! el is child.flatwalk(): Ah, I see what you mean. I think 'is' is 'in', but I kind of get the idea. This turns it into a generator method: And thanks for the generator versions too. I shall hack them in and poke them with a stick. Of course, for the above to work, "leaf" objects need a modified flatwalk method, e.g.: Yes, My 'stubs' (leaves) do have such, but I will edit to use yield. Thanks a mill. \d -- http://mail.python.org/mailman/listinfo/python-list
Re: Queue cleanup
Dennis Lee Bieber writes: > The nice thing about it [reference counting] is that it is sort > of deterministic -- one can examine code and determine that an object > is collected at some point in the execution... > Heap marking, OTOH, tends to run at indeterminate times, which could > have an impact if one needs predictable response timings Reference counting has the same problem. If you drop the last reference to a complex structure, it could take quite a long time to free all the components. By contrast there are provably real-time tracing gc schemes, including some parallelizeable ones. One reason CPython still can't run threads on parallel cores is it would have to lock the reference counts every time they're updated, and the slowdown from that is terrible. -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
On 28/08/2010 08:43, Peter Otten wrote: If you call functions within functions (or methods, it doesn't matter) they consume stack space Right, got it. Darn, but at least there's that setrecursionlimit call. Thanks, \e -- http://mail.python.org/mailman/listinfo/python-list
Re: Walking deeply nested lists
donn writes: > This is all about walking trees, recursion and generators. None of > which fit my brain at all! > > From an XML tree (an SVG file) I build a bunch of Tag objects. > > [I use lxml, but I am combining multiple svg files into a 'forest' of > trees, so I can't use the lxml walking methods because they all stop > at the 'end' of a branch where there is actually a 'link' over to > another tree.] > > Each Tag has a flatwalk() method. The return from that is a list which > can be deeply nested. As an example, something like this: > L=[1, [2, 3, [4, [5, 6], 7], 8], [9, 10] ] > > (The numbers in the example would actually be Tag Instances.) > > Aim 1 > --- > I'm trying to write a generator around such lists so that I can 'walk' them: > > for parent, child in mystery_generator(L): > print level, item > > Right now, I am running a 'flatten' function on the entire list (which > I don't savvy, I found it online) and then I iterate over that > flattened list. This doesn't feel right to me. (Code at end.) > > Aim 2 > --- > The Objects that represent the svg tags use that flatwalk() method to > build the nested list, I'd far prefer flatwalk() to be directly > useable in something like this way: > > for container, child in some_tag.flatwalk(): > print container, child > > The flatwalk() function is (and this is another puzzle see *) kind of > recursive. "For each of my children, tell that child to go > flatwalk()". > (Code at end.) > I am not sure how to turn such a thing into a generator. > > I keep wondering how os.walk() does its thing. My hierarchy of Tag > objects can be thought of as directories (tags:g, symbol, svg), files > (path, circle, etc.) and soft-links (use tags). > > * If an Instance calls a method on *another* Instance of the *same* > class, is this still recursion? And how does this 'stack up'? I mean, > literally, on the stack. Does each instance get its own stack, or does > all the push, call, pop stuff happen in one main stack? > (I worry about recursion depth limits because svg trees can get quite deep.) > > > The walking code so far: > > ## Found code. > def flatten(input): > output = [] > stack = [] > stack.extend(reversed(input)) > while stack: > top = stack.pop() > if isinstance(top, list): >stack.extend(reversed(top)) > else: >output.append(top) > return output not a bad idea. I would rather write it as: def flatten(input): output = [] stack = list(input) while stack: top = stack.pop() if isinstance(top, list): stack.extend(top) else: output.append(top) output.reverse() return output If you want to make it a generator function though, the initial version is better. All you need to do is: * change the line "output.append(top)" to "yield top" * delete the line "return output" Or you can go for the simple recursive approach: def flatten(lst): for el in lst: if isinstance(el, list): for x in flatten(el): yield x else: yield el > ## My walker > def test_walk(e): #lxml Element comes in > obj = ebag_get(e)['obj'] #get a tag object > l=obj.flatwalk() > ll= flatten(l) > #No current solution to get 'parent' in this iterator > #ie. for parent, child in ... > for tag in ll: > print tag > > Here's one of my Tag objects: > > class Brancher(object): > def __init__(self, elem): > self.elem = elem > self.children = [] > > def flatwalk(self): > l=[self] > for child in self.children: > l.append( child.flatwalk() ) #recur(ish)ion here > return l This flattens the list in the flatwalk method (which IMHO it should do given its name!): def flatwalk(self): flatlist = [self] for child in self.children: for el is child.flatwalk(): flatlist.append(el) return flatlist This turns it into a generator method: def flatwalk(self): yield self for child in self.children: for el is child.flatwalk(): yield el This turns it into a generator method which yields parents as well: def flatwalk(self, parent=None): yield self, parent for child in self.children: for el is child.flatwalk(self): yield el Then you can write: for tag, parent in mytag.flatwalk(): ... Of course, for the above to work, "leaf" objects need a modified flatwalk method, e.g.: Class LeafTag: def flatwalk(self, parent=None): yield self, parent HTH (warning: all code untested). -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: rfile.readline()
On Fri, Aug 27, 2010 at 10:57 PM, sarah wrote: > i want to know that what this function returns??? > > and what does this function do?? RTFM: http://docs.python.org/tutorial/inputoutput.html#methods-of-file-objects Honestly, it's the 2nd google hit for "python readline". Regards, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: rfile.readline()
sarah wrote: > i want to know that what this function returns??? > and what does this function do?? Where do you get rfile from? The readline() function (or method) could read one line from a file (likely) or wipe your harddisk (unlikely). Without some context it is impossible to tell. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: palindrome iteration
Richard Arts writes: > On Fri, Aug 27, 2010 at 10:51 PM, Jussi Piitulainen wrote: >> >> Meanwhile, I have decided to prefer this: >> >> def palindromep(s): >> def reversed(s): >> return s[::-1] >> return s == reversed(s) > > That seems like a bit of overkill... Why would you want to define a > function in a function for something trivial like this? Just > > def palindrome(s): > return s[::-1] > > will do fine. I'm sure your version will do something just fine, but what that something is, I can not tell. The body of your version is quite obscure and does not seem to agree with the name of the function. I find (s == reversed(s)) a clearer expression than (s == s[::-1]), and I found a simple way to use my preferred expression. > Of course, you can stick the inner function in a library somewhere > if you like. From my point of view, it would be an understatement to say that setting up a library for this would be an overkill. A simple local auxiliary function is nothing. -- http://mail.python.org/mailman/listinfo/python-list
