Re: [Tutor] Question on how to do exponents
On 07/02/12 01:01, Nate Lastname wrote: Exponents ... are **(or ^) Not quite the ^ operator is a bitwise XOR... 2^2 0 2^1 3 pow() is the other way to do exponents. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Rép. : Re: Issue with a shapefile (ArcGIS) library (pyshp) unpack requires a string argument of length 8
I just realized my first email was not very self explanatory, so let me
start over.
My system is Windows XP Professional, with Python 2.5, and the library
I'm experiencing trouble with is pyshp, available (single version for
all systems) here :
http://code.google.com/p/pyshp/
Here is the correct error message I get (I removed my failed attempt at
correcting the library, thanks for pointing that out Dave) :
Traceback (most recent call last):
File pyshell#3, line 1, in module
rsh=shreader.shapes()
File C:\Python25\shapefile.py, line 310, in shapes
shapes.append(self.__shape())
File C:\Python25\shapefile.py, line 222, in __shape
(recNum, recLength) = unpack(2i, f.read(8))
File C:\Python25\lib\struct.py, line 87, in unpack
return o.unpack(s)
error: unpack requires a string argument of length 8
My code can be summarized as that
f=shapefile.Editor(shapefile=C:\Sampler\Shpfiles\ROUTE.shp)
f.line(parts=[[coord[0],[0,0],[10,10]]])
f.record(i put my attributes here)
f.save('ROUTE')
The error happens when I do
shreader=shapefile.Reader(ROUTE.shp)
rsh=shreader.shapes()
afterwards.
@ Alex : I didn't read instead of editing, it was a typo in my initial
message, sorry but thanks anyway
@ Dave : There is no binary data in my file that I'm aware of, if you
mean in the shapefile, I reckon the library
takes care of it, otherwise it would'nt work at all ?
@ Nate : OK, but I do not understand where to put your correction ?
f.read(8) seems to be required to have a length of 8, due to the format
of the unpack (2i), but even though I tried to replace it with
f.read(8)[:8], it does not work.
Sorry again if I seem kinda slow, I'm really a beginner in python
coding.
ST
Савицкий Александрalexx...@gmail.com 06/02/2012 07:14
I am having a bit of trouble here with my code, which uses a shapefile
library, named pyshp, to import, edit, and save GIS files within
Python.
So, I open up my shapefile (data is polylines, meaning, not points or
polygons)
shapefile=shapefile.Reader(file.shp)
shps=shapefile.shapes()
shprec = shapefile.records()
Then I carry out some edits, and I save my file.
If you wish to edit your shapefiles, you need to create object:
shapefile.Editor() or
shapefile.Write() - if you want create new file.
and then save your edits...
shapefile.Reader object/class for READING shapefile, not for
edit/update
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Re: [Tutor] Backwards message program
myles broomes wrote: Im trying to code a program where the user enters a message and it is returned backwards. Here is my code so far: message = input(Enter your message: ) backw = counter = len(message) while message != 0: backw += message[counter-1] counter -= 1 print(backw) input(\nPress enter to exit...) When you want to do something with each item in a sequence, such as each character in a string, you can do it directly: for char in message: print(char) prints the characters one at a time. Python has a built-in command to reverse strings. Actually, two ways: the hard way, and the easy way. The hard way is to pull the string apart into characters, reverse them, then assemble them back again into a string: chars = reversed(message) # Gives the characters of message in reverse order. new_message = ''.join(chars) Or written in one line: new_message = ''.join(reversed(message)) Not very hard at all, is it? And that's the hard way! Here's the easy way: using string slicing. new_message = message[::-1] I know that's not exactly readable, but slicing is a very powerful tool in Python and once you learn it, you'll never go back. Slices take one, two or three integer arguments. Experiment with these and see if you can understand what slicing does and what the three numbers represent: message = NOBODY expects the Spanish Inquisition! message[0] message[1] message[39] message[38] message[-1] message[-2] message[0:6] message[:6] message[19:38] message[19:-1] message [19:-2] message[::3] message[:30:3] message[5:30:3] Hint: the two and three argument form of slices is similar to the two and three argument form of the range() function. Python gives you many rich and powerful tools, there's no need to mess about with while loops and indexes into a string and nonsense like that if you don't need to. As the old saying goes, why bark yourself if you have a dog? -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] decimal precision in python
Steve Willoughby wrote: On 06-Feb-12 07:25, Kapil Shukla wrote: i tried writing a small code to calculate option price using the binomial tree model. I compared my results with results of the same program in excel. There seems to be a minor difference due to decimal precision as excel is using 15 decimal precision and python (both 2.7 and 3.1) using 11. (at least that's what shown on shell) If you need lots of precision, you might consider using the decimal class. It'll cost you speed vs. the native floating-point type but won't cause you round-off errors. I'm afraid that's not correct. Decimal is still subject to rounding errors. from decimal import Decimal x = 1/Decimal(3) # one third, as close as a Decimal can give x + x + x == 1 False The difference is that the rounding errors you get with Decimal are usually different to the ones you get with binary floats. For example: y = 0.1 # one tenth, as close as a binary float can give y+y + y+y + y+y + y+y + y+y == 1 False while the same calculation is exact with Decimal. The reason for the error is the same in both cases: in the first, 1/3 takes an infinite number of decimal digits, while in the second, 1/10 takes an infinite number of binary digits. So Decimal 1/3 is not *precisely* 1/3, and float 1/10 is not precisely 1/10 either. Binary floats can store exactly any fraction which can be written as a sum of powers of 1/2, e.g.: 0.40625 = 13/32 = 1/4 + 1/8 + 1/32 so can be stored exactly in a float Every other number is rounded. The same applies to Decimal: it can store exactly any fraction which can be written as a sum of powers of 1/10. The advantage of Decimal is that anything which can be stored as an exact float can also be stored as an exact Decimal, plus some numbers which can't be written as exact floats. But there are still plenty of numbers which can't be stored exactly as either. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] decimal precision in python
Col, I think you wrote to me personally by accident, instead of to the Tutor list. Nothing you said seems to be private, so I've taken the liberty of answering back on the list. col speed wrote: Just an idea - I'm not an expert by any means, just a dabbler, but: many years ago, when I was looking at options(I assume you mean the same as me as in puts etc.) they were quoted as fractions. Some fractions can't be quoted as exact decimals and some decimals as binary, so fractions *may* be more exact. I believe there is a fractions module, but it is quite easy to create your own Rational class. Starting in Python 2.6, there is a fractions module in the standard library. Unlike float and Decimal, it is effectively infinite precision: from fractions import Fraction z = 1/Fraction(3) z + z + z == 1 True This comes at a cost, of course. Unless you are very careful, you can end up with fractions like this: Fraction(2573485501354569, 18014398509481984) That is very close to 1/7, and in fact it is the exact fraction equal to the binary float closest to 1/7: Fraction.from_float(1/7.0) Fraction(2573485501354569, 18014398509481984) So Fraction is not a panacea either. Unless you take care, you can easily end up using an unlimited amount of memory for an extremely precise number, when a much lower precision would be close enough -- or possibly even BETTER: Fraction.from_float(1/7.0).limit_denominator(10) Fraction(1, 7) But yes, Fractions are a sadly under-appreciated tool for numeric calculations. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] decimal precision in python
On 07-Feb-12 03:15, Steven D'Aprano wrote: Steve Willoughby wrote: If you need lots of precision, you might consider using the decimal class. It'll cost you speed vs. the native floating-point type but won't cause you round-off errors. I'm afraid that's not correct. Decimal is still subject to rounding errors. from decimal import Decimal x = 1/Decimal(3) # one third, as close as a Decimal can give x + x + x == 1 False Sorry, I guess I took it for granted that was understood. I was referring to round-off caused by binary representation of a number that by all appearances is a simple, rational, non-repeating decimal number expressed in base 10. In other words, when you're adding up financial figures, you'll get an accurate sum without mysterious rounding off, but of course certain fractions which don't have a straightforward way to represent as a decimal value, like 1/3, are going to be an issue. Good catch, though, it was better to point that out. -- Steve Willoughby / st...@alchemy.com A ship in harbor is safe, but that is not what ships are built for. PGP Fingerprint 4615 3CCE 0F29 AE6C 8FF4 CA01 73FE 997A 765D 696C ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question on how to do exponents
On 7 February 2012 13:49, Alan Gauld alan.ga...@btinternet.com wrote: On 07/02/12 01:01, Nate Lastname wrote: Exponents ... are **(or ^) Not quite the ^ operator is a bitwise XOR... 2^2 0 2^1 3 pow() is the other way to do exponents. Is is better to use pow() against **? -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ __**_ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/**mailman/listinfo/tutorhttp://mail.python.org/mailman/listinfo/tutor -- Sarma Tangirala, Class of 2012, Department of Information Science and Technology, College of Engineering Guindy - Anna University ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Backwards message program
On Tue, Feb 7, 2012 at 5:41 AM, Steven D'Aprano st...@pearwood.info wrote: myles broomes wrote: Im trying to code a program where the user enters a message and it is returned backwards. Here is my code so far: message = input(Enter your message: ) backw = counter = len(message) while message != 0: backw += message[counter-1] counter -= 1 print(backw) input(\nPress enter to exit...) When you want to do something with each item in a sequence, such as each character in a string, you can do it directly: for char in message: print(char) prints the characters one at a time. Python has a built-in command to reverse strings. Actually, two ways: the hard way, and the easy way. The hard way is to pull the string apart into characters, reverse them, then assemble them back again into a string: chars = reversed(message) # Gives the characters of message in reverse order. new_message = ''.join(chars) Or written in one line: new_message = ''.join(reversed(message)) Not very hard at all, is it? And that's the hard way! Here's the easy way: using string slicing. new_message = message[::-1] I know that's not exactly readable, but slicing is a very powerful tool in Python and once you learn it, you'll never go back. Slices take one, two or three integer arguments. Experiment with these and see if you can understand what slicing does and what the three numbers represent: message = NOBODY expects the Spanish Inquisition! message[0] message[1] message[39] message[38] message[-1] message[-2] message[0:6] message[:6] message[19:38] message[19:-1] message [19:-2] message[::3] message[:30:3] message[5:30:3] Hint: the two and three argument form of slices is similar to the two and three argument form of the range() function. Python gives you many rich and powerful tools, there's no need to mess about with while loops and indexes into a string and nonsense like that if you don't need to. As the old saying goes, why bark yourself if you have a dog? -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor While you should know about reverse, and understand slices, your program will work if you test for while counter != 0 instead of message. Message doesn't change message = input(Enter your message: ) backw = counter = len(message) #while message != 0: # not this while counter != 0: # this backw += message[counter-1] counter -= 1 print(backw) input(\nPress enter to exit...) -- Joel Goldstick ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Backspace Escape Sequence; \b
Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Thanks, Garland -- Sent via Mobile ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Backspace Escape Sequence; \b
Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Does $ python -c 'print this is b\bbo\bol\bld\bd' | less qualify? If you are using (e. g.) Linux this technique is used to show some text in boldface when you type something like help(str) in Python's interactive interpreter. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Backspace Escape Sequence; \b
Peter Otten wrote: Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Does $ python -c 'print this is b\bbo\bol\bld\bd' | less qualify? If you are using (e. g.) Linux this technique is used to show some text in boldface Gah, that has got to be the ugliest hack in the universe. I don't think that is guaranteed to work everywhere. less supports the \b trick, but the Python interactive interpreter doesn't support it directly. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question on how to do exponents
On 07/02/12 16:54, Sarma Tangirala wrote: Is is better to use pow() against **? I suspect ** will be faster since it doesn't have the function call overhead. But I haven't tried timing it. Feel free to do some tests and find out. Let us know how you get on! -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question on how to do exponents
Sarma Tangirala wrote: Is is better to use pow() against **? Advantages of ** - it is shorter to type x**y vs pow(x, y) - being an operator, it is slightly faster than calling a function - you can't monkey-patch it Disadvantages of ** - being an operator, you can't directly use it as a function-object - it can't take three arguments - hard to google for ** - you can't monkey-patch it Advantages of pow() - it is a function, so you can pass it around as an object - three argument form - easy to call help(pow) to see documentation - easy to google for pow - can be monkey-patched Disadvantages of pow() - a tiny bit slower due to the function call - slightly longer to type - can be monkey-patched Weigh up the advantages and disadvantages of each, and make the call which is better for you. (My preference is to use the ** operator.) -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Backspace Escape Sequence; \b
On 07/02/12 17:19, Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Do you mean backspace specifically or do you really mean backslash? In other words are you looking for a use of literal backspaces in a string or are you looking at the use of escaped characters in general? backspace specifically is not commonly used but is sometimes handy for positioning the cursor in the middle of a line. eg raw_input(Area:acres\b\b\b\b\b\b\b\b) Should output the prompt line with the cursor positioned in the gap between Area: and acres. raw_input(Area:acres\b\b\b\b\b\b\b\b) Area: 45 acres '45' But in the general sense there are lots of scenarios where we use escaped characters. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] (no subject)
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:but after breaking the for loop why the else command could not work?
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[Tutor] confusion with else command
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:
but after breaking the for loop why the else loop could not work?
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Re: [Tutor] Question on how to do exponents
On 8 February 2012 00:01, Steven D'Aprano st...@pearwood.info wrote: Sarma Tangirala wrote: Is is better to use pow() against **? Advantages of ** - it is shorter to type x**y vs pow(x, y) - being an operator, it is slightly faster than calling a function - you can't monkey-patch it Disadvantages of ** - being an operator, you can't directly use it as a function-object - it can't take three arguments - hard to google for ** - you can't monkey-patch it Advantages of pow() - it is a function, so you can pass it around as an object - three argument form - easy to call help(pow) to see documentation - easy to google for pow - can be monkey-patched Disadvantages of pow() - a tiny bit slower due to the function call - slightly longer to type - can be monkey-patched Weigh up the advantages and disadvantages of each, and make the call which is better for you. (My preference is to use the ** operator.) A simple function call argument would have done! :D Thanks for the survey! Anyway, I was wondering about this, if internally pow() actually uses **. :P -- Steven __**_ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/**mailman/listinfo/tutorhttp://mail.python.org/mailman/listinfo/tutor -- Sarma Tangirala, Class of 2012, Department of Information Science and Technology, College of Engineering Guindy - Anna University ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] confusion with else command
On 02/07/2012 01:52 PM, Debashish Saha wrote:
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:
but after breaking the for loop why the else loop could not work?
It works fine. The else clause of a for loop executes only if the loop
completes without breaking out.
If the language designers had wanted it to always execute, why have an
extra keyword?
--
DaveA
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Re: [Tutor] confusion with else command
Debashish Saha wrote:
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:
but after breaking the for loop why the else loop could not work?
The else suite is not invoked because that's the way Guido intended it ;)
It was designed for sitiuations like the following:
for beast in animals:
if is_it_a_cat(beast):
print(There's a cat among those animals)
break
else:
print(Sorry, there aren't any cats)
print(I've been looking for a cat) # you don't need an else for that
i. e. it's only invoked if the loop terminates normally (no break, and of
course no return or exception).
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Re: [Tutor] (no subject)
On Tue, Feb 7, 2012 at 7:50 PM, Debashish Saha silid...@gmail.com wrote:
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:but after breaking the for loop why the else command could not work?
because the else statement was designed to be that way:
http://docs.python.org/reference/compound_stmts.html#for
quoting the relevant part:
When the items are exhausted (which is immediately when the sequence
is empty), the suite in the else clause, if present, is executed, and
the loop terminates.
A break statement executed in the first suite terminates the loop
without executing the else clause’s suite.
in short, the else clause only executes if you do *not* break out of the loop.
HTH,
Hugo
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Re: [Tutor] Question on how to do exponents
On 02/07/2012 01:57 PM, Sarma Tangirala wrote: On 8 February 2012 00:01, Steven D'Apranost...@pearwood.info wrote: Sarma Tangirala wrote: Is is better to use pow() against **? Advantages of ** - it is shorter to type x**y vs pow(x, y) - being an operator, it is slightly faster than calling a function - you can't monkey-patch it Disadvantages of ** - being an operator, you can't directly use it as a function-object - it can't take three arguments - hard to google for ** - you can't monkey-patch it Advantages of pow() - it is a function, so you can pass it around as an object - three argument form - easy to call help(pow) to see documentation - easy to google for pow - can be monkey-patched Disadvantages of pow() - a tiny bit slower due to the function call - slightly longer to type - can be monkey-patched Weigh up the advantages and disadvantages of each, and make the call which is better for you. (My preference is to use the ** operator.) A simple function call argument would have done! :D Thanks for the survey! Anyway, I was wondering about this, if internally pow() actually uses **. :P I have no idea, but I'd assume so, unless there's a 3rd argument. At that point, the algorithm must change drastically. -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] For/Else loops
On Tue, Feb 7, 2012 at 1:50 PM, Debashish Saha silid...@gmail.com wrote:
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:but after breaking the for loop why the else command could not work?
Because that's the way a for/else statement works. The else suite is
only run if you do not break out of the loop. See the docs here:
http://docs.python.org/reference/compound_stmts.html#the-for-statement
Jerry
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Re: [Tutor] Backspace Escape Sequence; \b
Steven D'Aprano wrote: Peter Otten wrote: Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Does $ python -c 'print this is b\bbo\bol\bld\bd' | less qualify? If you are using (e. g.) Linux this technique is used to show some text in boldface Gah, that has got to be the ugliest hack in the universe. I don't think that is guaranteed to work everywhere. less supports the \b trick, but the Python interactive interpreter doesn't support it directly. Well, the beauty in that hack is that output devices that don't understand it usually interpret \b as backspace and thus still produce a readable fallback. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question on how to do exponents
On 2/7/2012 1:57 PM, Sarma Tangirala wrote: Anyway, I was wondering about this, if internally pow() actually uses **. :P from dis import dis dis(lambda a,b:a**b) 1 0 LOAD_FAST0 (a) 3 LOAD_FAST1 (b) 6 BINARY_POWER 7 RETURN_VALUE dis(lambda a,b:pow(a,b)) 1 0 LOAD_GLOBAL 0 (pow) 3 LOAD_FAST0 (a) 6 LOAD_FAST1 (b) 9 CALL_FUNCTION2 12 RETURN_VALUE Now you know, and you know how to find out! To delve any deeper you'd have to inspect the c source for pow. I'd assume it uses the c exponent operator -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] (no subject)
Do Not Use (no subject) as a subject!
Read the manual before asking questions like this. If you do not
understand the documentation tell us what you do not understand.
On 2/7/2012 1:50 PM, Debashish Saha wrote:
for i in range(1, 8):
print(i)
if i==3:
break
else:
print('The for loop is over')
Output:
1
2
3
Question:but after breaking the for loop why the else command could not work?
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--
Bob Gailer
919-636-4239
Chapel Hill NC
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[Tutor] dictionary of methods calling syntax
Hi list,
I'm trying to understand how to use a class-level dictionary to act as a switch
for class methods. In the contrived example below, I have the statistic name
as the key and the class method as the value.
class Statistics(object):
STAT = {
'MEAN': get_mean,
'SUM': get_sum,
}
def __init__(self, a, b):
self.a = a
self.b = b
def get_mean(self):
return (self.a + self.b) / 2.0
def get_sum(self):
return (self.a + self.b)
def get_stat(self, stat):
f = self.STAT[stat.upper()]
return f(self)
if __name__ == '__main__':
spam = Statistics(4, 3)
print spam.get_stat('mean')
print spam.get_stat('sum')
When I try to run this, I get:
NameError: name 'get_mean' is not defined
If I move the STAT dictionary to the bottom of the class, it works fine. I
understand why I get an error, i.e. when the dictionary is created get_mean
hasn't yet been defined, but I'm wondering if there is a better common practice
for doing this type of lookup. My web searches didn't come up with anything
too applicable.
thanks, matt
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Re: [Tutor] Tutor Digest, Vol 96, Issue 26
On Tue, Feb 7, 2012 at 10:57 AM, tutor-requ...@python.org wrote: Send Tutor mailing list submissions to tutor@python.org To subscribe or unsubscribe via the World Wide Web, visit http://mail.python.org/mailman/listinfo/tutor or, via email, send a message with subject or body 'help' to tutor-requ...@python.org You can reach the person managing the list at tutor-ow...@python.org When replying, please edit your Subject line so it is more specific than Re: Contents of Tutor digest... Today's Topics: 1. Re: Backspace Escape Sequence; \b (Peter Otten) 2. Re: Backspace Escape Sequence; \b (Steven D'Aprano) 3. Re: Question on how to do exponents (Alan Gauld) 4. Re: Question on how to do exponents (Steven D'Aprano) 5. Re: Backspace Escape Sequence; \b (Alan Gauld) 6. (no subject) (Debashish Saha) 7. confusion with else command (Debashish Saha) 8. Re: Question on how to do exponents (Sarma Tangirala) -- Message: 1 Date: Tue, 07 Feb 2012 18:41:12 +0100 From: Peter Otten __pete...@web.de To: tutor@python.org Subject: Re: [Tutor] Backspace Escape Sequence; \b Message-ID: jgrnmj$g41$1...@dough.gmane.org Content-Type: text/plain; charset=ISO-8859-1 Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Does $ python -c 'print this is b\bbo\bol\bld\bd' | less qualify? If you are using (e. g.) Linux this technique is used to show some text in boldface when you type something like help(str) in Python's interactive interpreter. -- Message: 2 Date: Wed, 08 Feb 2012 05:18:35 +1100 From: Steven D'Aprano st...@pearwood.info To: tutor@python.org Subject: Re: [Tutor] Backspace Escape Sequence; \b Message-ID: 4f316afb.7040...@pearwood.info Content-Type: text/plain; charset=ISO-8859-1; format=flowed Peter Otten wrote: Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Does $ python -c 'print this is b\bbo\bol\bld\bd' | less qualify? If you are using (e. g.) Linux this technique is used to show some text in boldface Gah, that has got to be the ugliest hack in the universe. I don't think that is guaranteed to work everywhere. less supports the \b trick, but the Python interactive interpreter doesn't support it directly. -- Steven -- Message: 3 Date: Tue, 07 Feb 2012 18:29:49 + From: Alan Gauld alan.ga...@btinternet.com To: tutor@python.org Subject: Re: [Tutor] Question on how to do exponents Message-ID: jgrqit$80s$1...@dough.gmane.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed On 07/02/12 16:54, Sarma Tangirala wrote: Is is better to use pow() against **? I suspect ** will be faster since it doesn't have the function call overhead. But I haven't tried timing it. Feel free to do some tests and find out. Let us know how you get on! -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ -- Message: 4 Date: Wed, 08 Feb 2012 05:31:07 +1100 From: Steven D'Aprano st...@pearwood.info To: tutor@python.org Subject: Re: [Tutor] Question on how to do exponents Message-ID: 4f316deb.3070...@pearwood.info Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sarma Tangirala wrote: Is is better to use pow() against **? Advantages of ** - it is shorter to type x**y vs pow(x, y) - being an operator, it is slightly faster than calling a function - you can't monkey-patch it Disadvantages of ** - being an operator, you can't directly use it as a function-object - it can't take three arguments - hard to google for ** - you can't monkey-patch it Advantages of pow() - it is a function, so you can pass it around as an object - three argument form - easy to call help(pow) to see documentation - easy to google for pow - can be monkey-patched Disadvantages of pow() - a tiny bit slower due to the function call - slightly longer to type - can be monkey-patched Weigh up the advantages and disadvantages of each, and make the call which is better for you. (My preference is to use the ** operator.) -- Steven -- Message: 5 Date: Tue, 07 Feb 2012 18:42:09 + From: Alan Gauld alan.ga...@btinternet.com To: tutor@python.org Subject: Re: [Tutor] Backspace Escape Sequence; \b Message-ID: jgrra2$ec8$1...@dough.gmane.org Content-Type: text/plain; charset=UTF-8; format=flowed On 07/02/12 17:19, Garland W. Binns wrote: Could someone please tell me a common or semi-frequent scenario in which a person would use a backspace escape sequence? Do you mean backspace specifically or do you really mean backslash? In other words
Re: [Tutor] dictionary of methods calling syntax
On Tue, Feb 7, 2012 at 2:32 PM, Gregory, Matthew
matt.greg...@oregonstate.edu wrote:
Hi list,
I'm trying to understand how to use a class-level dictionary to act as a
switch for class methods. In the contrived example below, I have the
statistic name as the key and the class method as the value.
class Statistics(object):
STAT = {
'MEAN': get_mean,
'SUM': get_sum,
}
def __init__(self, a, b):
self.a = a
self.b = b
def get_mean(self):
return (self.a + self.b) / 2.0
def get_sum(self):
return (self.a + self.b)
def get_stat(self, stat):
f = self.STAT[stat.upper()]
return f(self)
if __name__ == '__main__':
spam = Statistics(4, 3)
print spam.get_stat('mean')
print spam.get_stat('sum')
When I try to run this, I get:
NameError: name 'get_mean' is not defined
If I move the STAT dictionary to the bottom of the class, it works fine. I
understand why I get an error, i.e. when the dictionary is created get_mean
hasn't yet been defined, but I'm wondering if there is a better common
practice for doing this type of lookup. My web searches didn't come up with
anything too applicable.
thanks, matt
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You might want to read through this:
http://stackoverflow.com/questions/5213166/python-forward-declaration-of-functions-inside-classes
Specifically from an answer:
First, in class B, the function foo() is called before being
declared. A does not have this problem because foo() is only called
when the class is instantiated--after the function foo is defined.
So, I think you could move your STAT dictionary definition into the
__init__ method so that is doesn't actually run until you create an
instance of your class. That being said, I'm not sure that is more
'pythonic' than moving it to the bottom of the class definition
--
Joel Goldstick
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Re: [Tutor] dictionary of methods calling syntax
On 07/02/12 19:32, Gregory, Matthew wrote:
class Statistics(object):
STAT = {
'MEAN': get_mean,
'SUM': get_sum,
}
...
if __name__ == '__main__':
spam = Statistics(4, 3)
print spam.get_stat('mean')
print spam.get_stat('sum')
Since a class is effectively a disguised dictionary I'm not sure why you
want to do this? If you just want to access the method by name then why
not just call getattr(spam,'get_mean')?
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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Re: [Tutor] Tutor Digest, Vol 96, Issue 26
On 07/02/12 19:45, Michael Lewis wrote: As the instructions in the message you posted say... When replying, please edit your Subject line so it is more specific than Re: Contents of Tutor digest... And also please delete all the irrelevant stuff, it's almost impossible to spot the new material amongst all the other messages. Also it is inconsiderate to those who pay for their mail by the byte. -- Alan G Moderator. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Character Buffer Object Error
I want to find all digits in a string and then increment those digits by 1 and then return the same string with the incremented digits. I've tried the following code, but I am getting the following error. How do I do this properly? def AlterInput(user_input): print user_input new_output = '' for index, char in enumerate(user_input): if char.isdigit(): new_char = int(char) new_char += 1 new_output = ' '.join(user_input) new_output.replace(char, new_char) print new_output def GetUserInput(): '''Get a string from the user and pass it''' user_input = '''I got 432 when I counted, but Jim got 433 which is a lot for only 6 cats, or were there 12 cats?''' AlterInput(user_input.split()) Traceback (most recent call last): File C:/Python27/Homework/Homework 4_1.py, line 25, in module GetUserInput() File C:/Python27/Homework/Homework 4_1.py, line 23, in GetUserInput AlterInput(user_input.split()) File C:/Python27/Homework/Homework 4_1.py, line 15, in AlterInput new_output.replace(char, new_char) TypeError: expected a character buffer object Thanks. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Character Buffer Object Error
On 2012/02/08 07:56 AM, Michael Lewis wrote: I want to find all digits in a string and then increment those digits by 1 and then return the same string with the incremented digits. I've tried the following code, but I am getting the following error. How do I do this properly? def AlterInput(user_input): print user_input new_output = '' for index, char in enumerate(user_input): if char.isdigit(): new_char = int(char) new_char += 1 new_output = ' '.join(user_input) new_output.replace(char, new_char) print new_output def GetUserInput(): '''Get a string from the user and pass it''' user_input = '''I got 432 when I counted, but Jim got 433 which is a lot for only 6 cats, or were there 12 cats?''' AlterInput(user_input.split()) Traceback (most recent call last): File C:/Python27/Homework/Homework 4_1.py, line 25, in module GetUserInput() File C:/Python27/Homework/Homework 4_1.py, line 23, in GetUserInput AlterInput(user_input.split()) File C:/Python27/Homework/Homework 4_1.py, line 15, in AlterInput new_output.replace(char, new_char) TypeError: expected a character buffer object Thanks. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor new_char is of type int and not type str, so cast it back to a string before using it in your call to .replace as it expects both arguments to be strings. -- Christian Witts Python Developer // ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Character Buffer Object Error
Dear Michael Overall I see a few problems. 0. Functions should return values. Not print them 1. Why use enumerate? The code is not using the index anyway 2. The following line appears wrong. new_output = ' '.join(user_input) 3. This line has a very buggy possibility. new_output.replace(char, new_char) Let us say you have 234. First time you will replace 2 with 3, getting 334. And then you will replace the first 3 with 4 getting 434 and finally end up with 534. Of course due to other coding errors this does not come to pass. But your basic idea of using str.replace() is prone to this problem. 4. How are you supposed to treat 9? Anyway back to your problem: I want to find all digits in a string and then increment those digits by 1 and then return the same string with the incremented digits. Pseudocode -- Initialise and outstring (empty) Read the instring character by character if the current character is not a digit append it to outstring else append the transform(current char) to outstring If you can organize your code like this it may be easier HTH Regards Asokan Pichai ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
