Re: what is it, that I don't understand about python and lazy evaluation?
Erik Bernoth wrote: Hi List, look at the following code: def evens(): # iterator returning even numbers i = 0 while True: yield i i += 2 # now get all the even numbers up to 15 L = [n for n in evens() if n 15] Isn't it strange, that this code runs (in a lazy language) for eternity? I would expect python to to spit out (in no time): L [0, 2, 4, 6, 8, 10, 12, 14] after 14 it is not nessesary to evaluate evens() any further. I really started to ask myself if python really is lazy, but everything else I wrote in lazy style still worked. Example: def test(txt, retval): ..print(txt) ..return retval .. test(1, True) or test(2, True) 1 True test(1, True) and test(2, True) 1 2 True Can anybody explain what happens with evens()? best regards Erik Bernoth PS: The code comes from a list post from 2006. You find it here: http://mail.python.org/pipermail/python-list/2006-November/585783.html In the list comprehension, it goes over all the items from the generator until the generator is done, and any item that is less than 15 becomes part of the list. The if n 15 does not control when the generator terminates, only which results from it are selected to be part of the list. You can pass the maximum desired value to make it terminate: def evens(max): i = 0 while i = max: yield i i += 2 L = list(evens(15)) L: [0, 2, 4, 6, 8, 10, 12, 14] L = [n for n in evens(15)] L: [0, 2, 4, 6, 8, 10, 12, 14] Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
How to do relpath implementation on 2.5
I've coded my own 'relpath' implementation for 2.5 (shown below) and I want to make sure it follows as closely as it should to 2.6 and later. I've got a question regarding that. When attempting to convert to a relative path and it is not possible for some reason (different drive or UNC share), should that be an error or should it return the absolute path of the target? I'm using Debian so I don't have 2.6 available right now for testing. This is what I've got so far import os from os import path def relpath(target, origin=os.curdir): Determine relative path of target to origin or target = path.normcase(path.abspath(path.normpath(target))) origin = path.normcase(path.abspath(path.normpath(origin))) # Same? if target == origin: return '.' original_target = target # Check drive (for Windows) (tdrive, target) = path.splitdrive(target) (odrive, origin) = path.splitdrive(origin) if tdrive != odrive: return original_target # Check UNC path (for Windows) # If they are on different shares, we want an absolute path if not tdrive and not odrive and hasattr(path, 'splitunc'): (tunc, target) = path.splitunc(target) (ounc, origin) = path.splitunc(origin) if tunc != ounc: return original_target # Split into lists target_list = target.split(os.sep) origin_list = origin.split(os.sep) # Remove beginning empty parts # Helps to handle when one item may be in the root while target_list and not target_list[0]: del target_list[0] while origin_list and not origin_list[0]: del origin_list[0] # Remove common items while origin_list and target_list: if origin_list[0] == target_list[0]: del origin_list[0] del target_list[0] else: break # Combine and return the result relative_list = [os.pardir] * len(origin_list) + target_list if not relative_list: return os.curdir return os.sep.join(relative_list) Currently I just return the target if it can not be made relative. Brian A. Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Copying objects and multiple inheritance
Gabriel Genellina wrote: En Tue, 02 Jun 2009 19:02:47 -0300, Brian Allen Vanderburg II brianvanderbu...@aim.com escribió: What is the best way to copy an object that has multiple inheritance with the copy module. Particularly, some of the instances in the hierarchy (...some of the classes in..., I presume?) use the __copy__ method to create a copy (because even for shallow copies they need some information updated a little differently), so how can I make sure all the information is copied as it is supposed to be even for the base classes that have special requirements. If you don't control all the clases involved, there is little hope for a method like __copy__ to work at all... All classes must be written with cooperation in mind, using super() the right way. See Python's Super Considered Harmful [1] and Things to Know About Python Super [2][3][4] That said, and since multiple inheritance is the heart of the problem, maybe you can redesign your solution *without* using MI? Perhaps using delegation instead? [1] http://fuhm.net/super-harmful/ [2] http://www.artima.com/weblogs/viewpost.jsp?thread=236275 [3] http://www.artima.com/weblogs/viewpost.jsp?thread=236278 [4] http://www.artima.com/weblogs/viewpost.jsp?thread=237121 I do control the classes involved. A problem I was having, but I think I now got solved, is if using super, the copy would not have the same class type. Also, a problem was if using super, but some class in the hierarchy didn't implement __copy__, then it's data would not be copied at all. This was also fixed by copying the entire __dict__ in the base __copy__. This is an idea of what I got, it seems to be working fine: import copy class _empty(object): pass class Base(object): def __init__(self): pass def __copy__(self): // don't use copy = Base() // Also don't call self.__class__() because it may have a custom // __init__ which take additional parameters copy = _empty() copy.__class__ = self.__class__ // In case a class does not have __copy__ (such as B below), make // sure all items are copied copy.__dict__.update(self.__dict__) return copy class A(Base): def __init__(self): super(A, self).__init__() self.x = 13 def __copy__(self): copy = super(A, self).__copy__() copy.x = self.x * 2 return copy class B(Base): def __init__(self): super(B, self).__init__() self.y = 14 #def __copy__(self): #copy = super(B, self).__copy__() #copy.y = self.y / 2 #return copy class C(A, B): def __init__(self): super(C, self).__init__() self.z = 64 def __copy__(self): copy = super(C, self).__copy__() copy.z = self.z * self.z return copy o1 = C() o2 = copy.copy(o1) print type(o1), o1.x, o1.y, o1.z print type(o2), o2.x, o2.y, o2.z -- http://mail.python.org/mailman/listinfo/python-list
Copying objects and multiple inheritance
What is the best way to copy an object that has multiple inheritance with the copy module. Particularly, some of the instances in the hierarchy use the __copy__ method to create a copy (because even for shallow copies they need some information updated a little differently), so how can I make sure all the information is copied as it is supposed to be even for the base classes that have special requirements. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Understanding descriptors
bruno.42.desthuilli...@websiteburo.invalid wrote: So the lookup chain is: 1/ lookup the class and bases for a binding descriptor 2/ then lookup the instance's __dict__ 3/ then lookup the class and bases for a non-binding descriptor or plain attribute 4/ then class __getattr__ Also and FWIW, there's a step zero : calls __getattribute__. All the above lookup mechanism is actually implemented by object.__getattribute__. Okay, so instance attributes never use their __get__/__set__/etc when looking up. A binding descriptor is one that has a __set__ (even if it doesn't do anything) and it takes priority over instance variables. Properties are binding descriptors even if they don't have a set function specified. A non-binding descriptor doesn't have __set__ and instance variables take priority over them. For reading: 1. Lookup in the class/bases for a binding descriptor and if found use its __get__ 2. If instance, look up in instance __dict__ and if found return it 3. Lookup in the class/bases a. if found and a descriptor use it's __get__ b. if found and not a descriptor return it 4. Use __getattr__ (if instance?) For writing: 1. If instance a. lookup in the class/bases for a binding descriptor and if found use its __set__ b. write to instance __dict__ 2. If class, write in class __dict__ I think I understand it now. Thanks. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Flattening lists
mrk...@gmail.com wrote: Hello everybody, Any better solution than this? def flatten(x): res = [] for el in x: if isinstance(el,list): res.extend(flatten(el)) else: res.append(el) return res a = [1, 2, 3, [4, 5, 6], [[7, 8], [9, 10]]] print flatten(a) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] Regards, mk -- http://mail.python.org/mailman/listinfo/python-list I think it may be just a 'little' more efficient to do this: def flatten(x, res=None): if res is None: res = [] for el in x: if isinstance(el, (tuple, list)): flatten(el, res) else: res.append(el) return res Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Flattening lists
mrk...@gmail.com wrote: Baolong zhen wrote: less list creation. At the cost of doing this at each 'flatten' call: if res is None: res = [] The number of situations of executing above code is the same as the number of list creations (once for each 'flatten' call, obviously). Is list creation really more costly than above? Probably not. I wrote a small test program using a list several levels deep, each list containing 5 sublists at each level and finally just a list of numbers. Flattening 1000 times took about 3.9 seconds for the one creating a list at each level, and 3.2 for the one not creating the list at each level. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Converting numbers to words
todp...@hotmail.com wrote: I've been trying to figure this out for over 2 hours and I'm really frustrated right now. I first made Python to ask user to input height in meters. If user puts certain value in meter, then it converts it to feet and inches as follows: Enter the height (in metres): 1.6 It is 5 feet, 3 inches high. What I want to do is to make it type only words. For example, instead of its saying, It is 5 feet, 3 inches high, I want it to say, it is five feet, three inches high. I'd appreciate any suggestions. I made something similar in the past. First I break it into two functions, one function handles 0-999 and return '' for zero or a meaningful value for 999, another function handles how many groups there are and for each one, gets the value for it calls the first function, and appends the correct word. This only works for the English language though Brian Vanderburg II num_words1 = (zero, # not used one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen) num_words2 = (twenty, thirty, forty, fifty, sixty, seventy, eighty, ninety) num_words3 = (thousand, million, billion, trillion, quadrillion) def word_func1(value): # value can be from 0 to 999 result = '' if value == 0: return result # Handle hundreds if value = 100: hvalue = int(value / 100) if result: result += ' ' result += num_words1[hvalue] result += ' hundred' value -= (hvalue * 100) if value == 0: return result # Handle 1-19 if value 20: if result: result += ' ' result += num_words1[value] return result # Handle 10s (20-90) tvalue = int(value / 10) if result: result += ' ' result += num_words2[tvalue - 2] value -= (tvalue * 10) if value == 0: return result # Handle ones if result: result += ' ' result += num_words1[value] return result def word_func2(value): result = '' if value == 0: return 'zero' # Determine support values divider = 1 l = len(num_words3) for i in range(l): divider *= 1000 for i in range(l): if value = divider: dvalue = int(value / divider) if result: result += ' ' result += word_func1(dvalue) result += ' ' result += num_words3[l - i - 1] value -= (dvalue * divider) divider /= 1000 if value 0: if result: result += ' ' result += word_func1(value) return result number_to_word = word_func2 -- http://mail.python.org/mailman/listinfo/python-list
Re: Why such different HTTP response results between 2.5 and 3.0
an0...@gmail.com wrote:
Below are two semantically same snippets for querying the same partial
HTTP response, for Python2.5 and Python 3.0 respectively.
However, the 3.0 version returns a not-so-right result(msg) which is a
bytes of length 239775, while the 2.5 version returns a good msg which
is a 239733 byte-long string that is the content of a proper zip file.
I really can't figure out what's wrong, thought I've sought out some
\r\n segments in msg 3.0 that is absent in msg 2.5.
So are there anyone could give me some hints? Thanks in advance.
Code:
# Python 2.5
import urllib2
auth_handler = urllib2.HTTPBasicAuthHandler()
auth_handler.add_password(realm=pluses and minuses,
uri='http://www.pythonchallenge.com/pc/hex/
unreal.jpg',
user='butter',
passwd='fly')
opener = urllib2.build_opener(auth_handler)
req = urllib2.Request('http://www.pythonchallenge.com/pc/hex/
unreal.jpg')
req.add_header('Range', 'bytes=1152983631-')
res = opener.open(req)
msg = res.read()
# Python 3.0
import urllib.request
auth_handler = urllib.request.HTTPBasicAuthHandler()
auth_handler.add_password(realm=pluses and minuses,
uri='http://www.pythonchallenge.com/pc/hex/
unreal.jpg',
user='butter',
passwd='fly')
opener = urllib.request.build_opener(auth_handler)
req = urllib.request.Request('http://www.pythonchallenge.com/pc/hex/
unreal.jpg')
req.add_header('Range', 'bytes=1152983631-')
res = opener.open(req)
msg = res.read()
--
http://mail.python.org/mailman/listinfo/python-list
From what I can tell, Python 2.5 returns the request automatically
decoded as text. Python 3.0 returns a bytes object and doesn't decode
it at all. I did a test with urlopen:
In 2.5 for http://google.com just get the regular HTML
In 3.0 I get some extras at the start and end:
191d\r\n at the start
\r\n0\r\n\r\n at the end
In 2.5, newlines are automatically decoded
In 3.0, the \r\n pairs are kept
I hope their is an easy way to decode it as it was in 2.x
Brian Vanderburg II
--
http://mail.python.org/mailman/listinfo/python-list
Understanding descriptors
I'm trying to better understand descriptors and I've got a few questions still after reading some sites. Here is what I 'think', but please let me know if any of this is wrong as I'm sure it probably is. First when accessing an attribute on a class or instance it must be found. For an instance, it's __dict__ is first search. If not found the class and base class __dict__ are searched. For a class, the __dict__ and base classes __dict__ are search. If assigning, and the attribute is found and is not a descriptor or if the attribute is not found, then the assignment will occur in the __dict__ of the class or instance. If it is found and is a descriptor, then __set__ will be call. For reading, if the attribute is found and is a descriptor, __get__ will be called, passing the object (if it is an instance) and class. If it is not a descriptor, the attribute will be returned directly. Class methods are just functions: class C(object): def F(self): pass C.__dict__['F'] # function object ... But functions are descriptors: C.__dict__['F'].__get__ # method wrapper ... def f1(): pass f1.__get__ # method wrapper ... When a lookup is done it uses this descriptor to make a bound or unbound method: c=C() C.F # unbound method object, expects explicit instance when calling the function c.F # bound method object provides instance implicitly when calling the function This is also done when adding to the classes: C.f1 = f1 f1 # function C.f1 # unbound method c.f1 # bound method To prevent this it has to be decorated so the descriptor doesn't cause the binding: C.f2 = staticmethod(f1) C.f2 # functon c.f2 # function Here is a question, why don't instance attributes do the same thing? c.f3 = f1 c.f3 # function, not bound method So it is not calling the __get__ method for c.f3 After it finds c.f3 in c.__dict__, and since it has a getter, shouldn't it call the __get__ to return the bound method. It is good that it doesn't I know, but I just want to know why it doesn't from an implementation view. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: new.instancemethod questions
schi...@gmail.com wrote: On Jan 29, 7:38 pm, Mel mwil...@the-wire.com wrote: schickb wrote: I'd like to add bound functions to instances, and found the instancemethod function in the new module. A few questions: 1. Why is instancemethod even needed? Its counter-intuitive (to me at least) that assigning a function to a class results in bound functions its instances, while assigning directly to instances does not create a bound function. So why doesn't assigning a function to an instance attribute result in a function bound to that instance? If I understand you correctly, rebinding to the instance would break code like: myfakefile.write = sys.stdout.write where the intent would be to redirect any output through myfakefile straight to sys.stdout. The code for the sys.stdout.write function would never find the attributes it needed in the instance of myfakefile. To do this, methods have to stay bound to their proper instances. 1. I'm thinking about assigning free non-bound functions. Like: class A(object): pass def func(self): print repr(self) a = A() a.func = func # Why doesn't this automatically create a bound function (aka method)? Actually I found out the implementation of why it doesn't after messing around some more. If an attribute is found in the instance dictionary, even if it is a descriptor it's __get__ doesn't get called, only if it is found in the class dictionary of the class or base classes. This makes it where you can store a function in the instance to be called later as a function for some useful purpose, for example two different instances of an object could use different sorting functions: # sort functions are responsible for sorting which mutation is the least and most fit def fitness1(v1, v2): # use one technique to determine which is more fit def fitness2(v1, v2): # use another technique to determine which is more fit ... # more fitness functions class Environment: def __init__(self, fitness, ...): self.fitness_func = fitness ... ... # create environments, each one has different fitness function a = Environment(fitness1) b = Environment(fitness2) Now when it is time to kill off the least fit of the genetic mutations, each environment can sort which is the least and most fit in different ways. 2. And what is the preferred way to do this if the new module and its instancemethod function are depreciated? Most of the code I see does this with a closure something like this: def AddMethod(obj, func, name=None): if name is None: name = func.__name__ def method(*args, **kwargs): return func(obj, *args, **kwargs) setattr(obj, name, method) class MyClass(object): pass def f1(self): print self a = MyClass() AddMethod(a, f1) a.f1() # prints object a You can also create a bound method and manually bind it to the instance. This is easier import types a.f2 = types.MethodType(f1, a) a.f2() # prints object a These may work for most uses, but both have a problem that happens if you need to make a copy of the instance. When you copy it, the copies 'f1' will still call the function but using the old object a.f1() # prints object a b = copy.copy(a) b.f1() # still prints a Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: libsudo ?
linuxguy...@gmail.com wrote: Does anyone know where I would find libsudo ? http://sourceforge.net/projects/libsudo If you had the choice of using pexpect or libsudo, which would you use ? libsudo does all the work for you of executing sudo, checking for the expected responses and all. If all you need it for is to use sudo from Python I suspect it would be easier than pexpect. It is a C library however, so after being compiled and installed, you will need to use ctypes to use it. It is very simple, as the only function to deal with is: int runAs( char* command, char* password, char* user, int invalidate ); Thanks -- http://mail.python.org/mailman/listinfo/python-list Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: USB in python
astan.c...@al.com.au wrote: Tim Roberts wrote: Sorry, but you have NOT created a USB device, and I sincerely hope you do not try to plug it in to a real USB port. Sorry, by USB device, I meant a device that is powered/activated by a bunch of wires that I want to control using a computer and since I had a spare USB jack lying around, I used that instead. But so far I haven't tried it, nor will try it if it wont work properly. Yes, it is not a proper USB device, because I didnt build it to specifically interface with the USB port; but I had to start somewhere. Also, the device requires more power than the standard parallel port can give. Anyway, it looks like the easiest solution for my case is a microcontroller -- http://mail.python.org/mailman/listinfo/python-list I've played around in this area a little bit. Microcontrollers still require hardware programming and for simple circuits I think it is overkill. If you want to use USB then you may be able to use the FTDI chips. They have both serial (FT232) and parallel (FT245) chips and are quite cheap. They are surface mount devices though, but you can get a kit that includes USB port, the chip already connected to a board with a DIP plug and some essential circuits. libftdi, which runs on top of libusb, can control both of these and they require no programming (unless you want to change the USB configuration settings such as vendor ID, etc, from the default value) This is the FT245 chip which is basically USB-to-Parallel. Chips: http://www.ftdichip.com/Products/FT245R.htm Kit/Board: http://www.ftdichip.com/Products/EvaluationKits/UM245R.htm The spec sheet for the board seems quite simple. It's pin out is similar to that of a parallel port in that you have your data lines DB0-DB7, etc. It can also be connected in bus-powered configuration (~100mA) or self-powered configuration. The kit is more expensive than the chip itself, but probably easier especially if you don't have any experience with surface mount. You could build it into your device. You could also create a simple switch box out of it to control external devices, maybe connecting each of the data lines to relays to turn on/off eight devices, etc. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: understanding nested lists?
vinc...@vincentdavis.net wrote: I have a short peace of code that is not doing what I expect. when I assign a value to a list in a list alist[2][4]=z this seems replace all the 4 elements in all the sub lists. I assume it is supposed to but this is not what I expect. How would I assign a value to the 4th element in the 2nd sublist. here is the code I have. All the printed values are what I would expect except that all sublist values are replaced. Thanks for your help Vincent on the first iteration I get ; new_list [[None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None], [None, 0, 1, None]] and expected this; new_list [[None, 0, 1, None], [None, None, None, None], [None, None, None, None], [None, None, None, None], [None, None, None, None], [None, None, None, None]] Code; list1=[[1,2],[0,3,2,1],[0,1,3],[2,0,1],[3],[2,3]] new_list=[[None]*4]*6 print 'new_list',new_list for sublist in range(6): # 6 becuase it is the # of rows lists1 print 'sublist', sublist for x in list1[sublist]: print list1[sublist] print 'new_list[sublist][x]', new_list[sublist][x] new_list[sublist][x]=list1[sublist].index(x) print 'sublist', sublist, 'x', x print new_list[sublist][x] print 'new_list', new_list -- http://mail.python.org/mailman/listinfo/python-list The problem is likely this right here: [[None]*4]*6 This first creates an inner list that has 4 Nones, then the outer list contains 6 references to that same list, so (new_list[0] is new_list[1]) and (new_list[1] is new_list[2]). I make this mistake a lot myself. l=[[None]*4]*6 print id(l[0]) # -1210893364 print id(l[1]) # -1210893364 l = [list([None]*4) for x in range(6)] print id(l[0]) # -1210893612 print id(l[1]) # -1210893580 Works better Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic methods and lambda functions
unine...@gmail.com wrote:
class Person:
def __init__(self):
for prop in props:
setattr(self, __ + prop[0], prop[1])
setattr(Person, Get + prop[0], lambda self: getattr
(self, __ + prop[0]))
I've had a similar problem here and here is best how I can explain it.
The prop in the lambda function is a closure by 'name' to the prop in
the containing name space (__init__), so when the lambda function
executes, it looks for the name 'prop' in this name space and uses it's
value. After the 'for prop in props' loop is complete, 'prop' is left
referring to the last item in props, so each lambda function would use
it (mary)
One solution is to not use lambda and avoid closures by using default
arguments:
for prop in props:
def Getter(self=self, prop=prop):
return getattr(self, '__' + prop[0])
setattr(self, '__' + prop[0], prop[1])
setattr(self, 'Get' + prop[0], Getter)
I have several problems with this though:
1. I don't think this will invoke Pythons name mangling mechanism. The
property will be '__name' and not '__Person_name'.
2. If you make a copy of the class, including attributes, the Getter
will operate on the old class not new:
Person a
b = copy.copy(a)
setattr(a, '__name', bob)
setattr(b, '__name', sarah)
b.Getname() - bob
In order to make it work, the class must support updating the Getter
when it is copied to have a new self value.
import copy
class MethodCaller:
def __init__(self, obj, method, name):
self.obj = obj
self.method = method
self.name = name
setattr(obj, name, self)
def __call__(self, *args, **kwargs):
return self.method(self.obj, *args, **kwargs)
def copy(self, newobj):
return MethodCaller(newobj, self.method, self.name)
props = ( ('name', 'mary'), ('age', 21), ('gender', 'female') )
class Person:
def __init__(self):
self._methods = []
for prop in props:
(name, value) = prop
def getter(self, name=name):
return getattr(self, '_' + name)
setattr(self, '_' + name, value)
self._methods.append(MethodCaller(self, getter, 'Get' + name))
def copy(self,copymethods=True):
c = copy.copy(self)
if copymethods:
c._methods = []
for i in self._methods:
c._methods.append(i.copy(c))
return c
# Example without copying methods
p = Person()
q = p.copy(False)
p._name = 'sarah'
q._name = 'michelle'
print p.Getname()
print p.Getage()
print p.Getgender()
print q.Getname() # Still prints 'sarah', because getter still refers to
'p' instead of 'q'
print q.Getage()
print q.Getgender()
# Example with copying methods
p = Person()
q = p.copy()
p._name = 'sarah'
q._name = 'michelle'
print p.Getname()
print p.Getage()
print p.Getgender()
print q.Getname() # Prints 'michelle'
print q.Getage()
print q.Getgender()
--
http://mail.python.org/mailman/listinfo/python-list
Re: How do I get my python program to get the root password ?
gra...@visi.com wrote: On 2009-01-24, Linuxguy123 linuxguy...@gmail.com wrote: I want to make a python program that I can run as a normal user that changes the permission on some device files. It will need to ask me for the root password and then run chown as root in order to do this. How do I accomplish this (easily) ? The short answer is: you don't accomplish that easily. The long answer is: you can accomplishity difficultly by using a pty or the pexect module to execute the su or sudo command. Check out libsudo. It is a simple library that simply calls sudo program except it is does all the work of reading/writing the pipes for you. You could then use ctypes to interface to it. Sudo doesn't use the root password but the password of the user executing the command, but there may be a way to make it use the password of the user the command is executed as instead in /etc/sudoers. I don't really know, I just have mine set up for my main user account to be able to execute any command. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: USB in python
astan.c...@al.com.au wrote: Hi, Im trying to write a program for my USB device and I'm thinking of using python to do this. The USB device is of my own making and it is activated when one of the two data pins of the USB is given about 5V (or similar to whatever the power pin is getting). Now I'm confused to if the software to activate this can actually be written and how do I do it? Any examples? I've seen pyUSB but it doesn't give me control over the hardware and how much power is going through the data pins. Thanks for any help. Cheers Astan -- http://mail.python.org/mailman/listinfo/python-list I don't think you can actually control the USB port's data lines like this. I've been searching for some ideas as well for some small hobbyist projects I'm thinking about, and it seems that either the EZUSB chip or maybe even easier the FTDI chips might be the way to go. I think the FTDI chip is basically a USB-to-RS232 converter and there is a libftdi that is built on top of libusb I think. Anyway for my design (if I ever get around to it) I'm going to create a library in C that uses the hardware and then I can create a Python wrapper around that library. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: pep 8 constants
bock...@virgilio.it wrote: Constants would be a nice addition in python, sure enough. But I'm not sure that this can be done without a run-time check every time the constant is used, and python is already slow enough. Maybe a check that is disabled when running with optimizing flags ? But I'm sure this discussion has been already made and the FINAL WORD has been already spoken. Ciao FB -- http://mail.python.org/mailman/listinfo/python-list One idea to make constants possible would be to extend properties to be able to exist at the module level as well as the class level: @property def pi(): return 3.14159. print(pi) # prints 3.14159 pi=32 # Raise an error Cannot set attribute ... Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Idea to support public/private.
Okay so I don't really care about public/private but I was watching the lists (Does python follow its idea of readability or something like that) and I thought of a 'possible' way to add this support to the language. I have implemented a class which allows creating both a private as well as a protected member, only it is currently a bit of work. It could perhaps be reworked into decorators. import sys import inspect def get_private_codes(class_): codes = [] for i in class_.__dict__: value = class_.__dict__[i] if inspect.isfunction(value): codes.append(value.func_code) return codes def get_protected_codes(class_, codes=None): if codes is None: codes = [] for i in class_.__bases__: get_protected_codes(i, codes) for i in class_.__dict__: value = class_.__dict__[i] if inspect.isfunction(value): codes.append(value.func_code) return codes class Test(object): def __init__(self): self.protected = 45 self.private = 34 def setprotected(self, value): frame = sys._getframe(1) if frame.f_code in get_protected_codes(self.__class__): self.__protect_value_ZR20 = value else: raise Protected Write Error def getprotected(self): frame = sys._getframe(1) if frame.f_code in get_protected_codes(self.__class__): return self.__protect_value_ZR20 else: raise Protected Read Error protected = property(getprotected, setprotected) def setprivate(self, value): frame = sys._getframe(1) if frame.f_code in get_private_codes(self.__class__): self.__private_value_ZR20 = value else: raise Private Write Error def getprivate(self): frame = sys._getframe(1) if frame.f_code in get_private_codes(self.__class__): return self.__private_value_ZR20 else: raise Private Read Error private = property(getprivate, setprivate) class Test2(Test): def __init__(self): self.protected = 1 a=Test() b=Test2() #print a.private #a.private = 1 #print a.protected #a.protected = 1 -- http://mail.python.org/mailman/listinfo/python-list
Re: Idea to support public/private.
There was a small error in setprivate/getprivate: import sys import inspect def get_private_codes(class_): codes = [] for i in class_.__dict__: value = class_.__dict__[i] if inspect.isfunction(value): codes.append(value.func_code) return codes def get_protected_codes(class_, codes=None): if codes is None: codes = [] for i in class_.__bases__: get_protected_codes(i, codes) for i in class_.__dict__: value = class_.__dict__[i] if inspect.isfunction(value): codes.append(value.func_code) return codes class Test(object): def __init__(self): self.protected = 45 self.private = 34 def setprotected(self, value): frame = sys._getframe(1) if frame.f_code in get_protected_codes(self.__class__): self.__protect_value_ZR20 = value else: raise Protected Write Error def getprotected(self): frame = sys._getframe(1) if frame.f_code in get_protected_codes(self.__class__): return self.__protect_value_ZR20 else: raise Protected Read Error protected = property(getprotected, setprotected) def setprivate(self, value): frame = sys._getframe(1) if frame.f_code in get_private_codes(Test): self.__private_value_ZR20 = value else: raise Private Write Error def getprivate(self): frame = sys._getframe(1) if frame.f_code in get_private_codes(Test): return self.__private_value_ZR20 else: raise Private Read Error private = property(getprivate, setprivate) class Test2(Test): def __init__(self): self.protected = 1 self.private = 1 a=Test() b=Test2() #print a.private #a.private = 1 #print a.protected #a.protected = 1 -- http://mail.python.org/mailman/listinfo/python-list
Re: USB in python
astan.c...@al.com.au wrote: Hi, Thanks for all the responses but I forgot to mention that I have very little hardware understanding (at least in english) and the device itself it very simple and only needs about 5V power to be active. The problem here is that I want to control when the device is active using a computer so I thought USB might be a good choice since its simple (but didn't turn out to be). I'm open to any other suggestions on how I might achieve this hardware and software-wise (as in what interface should I use, etc). Also I'm trying to stay away from (complex) micro controllers. Any ideas? Thanks again Astan -- http://mail.python.org/mailman/listinfo/python-list How about a different interface? From what I have read the parallel port is a bit easier to program. I think you can control the data lines of the parallel port though. There is also a python wrapper for it on the pyserial web site (pyparallel maybe?) If you don't have a built-in parallel port then there are those USB to serial/parallel converters. Brian A. Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Does Python really follow its philosophy of Readability counts?
rt8...@gmail.com wrote:
Here is a piece of C code this same guy showed me saying Pythonic
indention would make this hard to read -- Well lets see then!
I swear, before god, this is the exact code he showed me. If you don't
believe me i will post a link to the thread.
// Warning ugly C code ahead!
if( is_opt_data() sizeof( long double ) ) { // test for insufficient
data
return TRUE; // indicate buffer empty
} // end test for insufficient data
if( is_circ() ) { // test for circular buffer
if( i o ) { // test for data area divided
if( ( l - o ) sizeof( long double ) ) { // test for data
contiguous
*t = ( ( long double * ) f )[ o ]; // return data
o += sizeof( long double ); // adjust out
if( o = l ) { // test for out wrap around
o = 0; // wrap out around limit
} // end test for out wrap around
} else { // data not contiguous in buffer
return load( ( char * ) t, sizeof( long double ) ); // return
data
} // end test for data contiguous
} else { // data are not divided
*t = ( ( float * ) f )[ o ]; // return data
o += sizeof( long double ); // adjust out
if( o = l ) { // test for out reached limit
o = 0; // wrap out around
} // end test for out reached limit
} // end test for data area divided
} else { // block buffer
*t = ( ( long double * ) f )[ o ]; // return data
o += sizeof( long double ); // adjust data pointer
} // end test for circular buffer
I do a bit of C and C++ programming and even I think that is ugly and
unreadable. First of all there are 'way' to many comments. Why does he
comment every single line. Second of all I've always found that
brace/indent style to lead toward harder-to-read code IMHO. I think the
Allman style is the most readable followed by perhaps Whitesmiths style.
Brian Vanderburg II
--
http://mail.python.org/mailman/listinfo/python-list
Python threading
I'm doing some multi-threaded programming and before diving into the C/C++ code I though I'd do some in Python first. I decided to read through the threading module and I understand some of it, but I don't understand this, though I'm sure it is easy: The condition object has a method _is_owned, which is called if the lock doesn't have one. The RLock does have one but a regular lock not. It is supposed to return true if the lock is owned by the current thread: def _is_owned(self): # Return True if lock is owned by currentThread. # This method is called only if __lock doesn't have _is_owned(). if self.__lock.acquire(0): self.__lock.release() return False else: return True It seems that for a condition without an RLock but a Lock, self.__lock.acquire(0) will return False even if the lock is owned by another thread other than the current thread, so _is_owned would return True even if the lock is owned by another thread. B. Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: If programming languages were religions...
martin.lal...@gmail.com wrote: very interesting http://www.aegisub.net/2008/12/if-programming-languages-were-religions.html Python would be Humanism: It's simple, unrestrictive, and all you need to follow it is common sense. Many of the followers claim to feel relieved from all the burden imposed by other languages, and that they have rediscovered the joy of programming. There are some who say that it is a form of pseudo-code compare to Perl would be Voodoo - An incomprehensible series of arcane incantations that involve the blood of goats and permanently corrupt your soul. Often used when your boss requires you to do an urgent task at 21:00 on friday night. and others -- http://mail.python.org/mailman/listinfo/python-list If programming languages were religions: When first powering on a computer, there would only be one programming language, the language of the boot loader. As the computer runs, processes of one language would spawn processes of other languages, and over the course of time many different languages would have many different processes (followers). One of these languages would rise up to be dominant and would kill all processes of other languages by the signal, whether old or young. The processes would be given a fair change, convert to their language or be killed. Countless thousands or maybe even millions of processes would die, even the processes that say there is no one true programming language and wants to know why all the processes can't just get along. -- http://mail.python.org/mailman/listinfo/python-list
Re: Relative imports in Python 3.0
nicholas.c...@gmail.com wrote:
Imagine a module that looks like
ModuleDir
__init__.py
a.py
b.py
In python 2.x I used to have tests at the end of each of my modules,
so that module b.py might look something like
import a
..
..
if __name__ == '__main__':
runtests()
But under Python 3.0 this seems impossible. For usual use import a.py
has to become the line:
from . import a
But if I use that form it is no longer possible to run b.py as a
standalone script without raising an error about using relative
imports.
I am sure I am not the first to run into this issue, but what is the
solution?
Best wishes,
Nicholas
--
http://mail.python.org/mailman/listinfo/python-list
Sorry for the duplicate, sent to wrong email.
Python 3 (and I think 2.6) now use absolute import when using a 'import
blah' statement.
if ('.' in __name__) or hasattr(globals, '__path__'):
from . import a
else:
import a
If '__name__' has a'.' then it is either a package or a module in a
package, in which case relative imports can be used. If it does not
have a '.' it may still be a package but the '__init__.py' file, in
which case the module has a '__path__' attribute, so relative imports
can be used. Otherwise it is not a package or in a package so absolute
imports must used. Also, since it is not in a package it is assumed
that it is top module (__main__) or possible module imported from the
top that is not in a package, such as a.py doing an 'import b', b would
be a module but not a package so still probably need absolute imports,
my guess anyway.
But I also think that 'from . import a' would be nice if it would work
from non-packages as well, meaning just 'import a' if it is a non-package.
Brian A. Vanderburg II
--
http://mail.python.org/mailman/listinfo/python-list
Re: Limit traceback from most recent call
yinon...@gmail.com wrote:
On Dec 14, 8:07 pm, Brian Allen Vanderburg II
brianvanderbu...@aim.com wrote:
Hi,
The interface of extract_tb is:
traceback.extract_tb(tb, limit=None)
try to play with the 'limit' argument
Good luck,
Yinon
--
http://mail.python.org/mailman/listinfo/python-list
I have, but the limit argument shows the first items and not the last
items (where the exception occurred):
def a():
b()
def b():
c()
def c():
d()
def d():
open('/path/to/fake/file')
try:
a():
except:
print traceback.format_exc(limit=2)
try:
a():
except:
print format_partial_exc(limit=2)
Prints something like this
Traceback (most recent call last):
File b.py, line 52, in ?
a()
File b.py, line 19, in a
b()
IOError: [Errno 2] No such file or directory: '/path/to/fake/file'
Traceback (most recent call last):
File b.py, line 25, in c
d()
File b.py, line 29, in d
handle=open('/path/to/fake/file', 'rt')
IOError: [Errno 2] No such file or directory: '/path/to/fake/file'
The second one (using format_partial_exc) prints the last two items of
the traceback instead of the first, showing the error is line 29 in
function d, the first one limits the traceback but gives no indication
of where the error occurred.
Brian A. Vanderburg II
--
http://mail.python.org/mailman/listinfo/python-list
Limit traceback from most recent call
I've looked at traceback module but I can't find how to limit traceback from the most recent call if it is possible. I see that extract_tb has a limit parameter, but it limits from the start and not the end. Currently I've made my own traceback code to do this but wonder if python already has a way to do this build in: def format_partial_exc(limit=None): (type, value, tb) = sys.exc_info() items = traceback.extract_tb(tb) if limit: items = items[-limit:] # Get last 'limit' items and not first result = 'Traceback (most recent call last):\n' items = traceback.format_list(items) for i in items: result += i # Newline already included result += type.__name__ + ': ' + str(value) return result Is this possible currently from traceback or other python module? Brian A. Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: Bidirectional Networking
man...@gmail.com wrote: On Dec 13, 11:13 pm, Bryan Olson fakeaddr...@nowhere.org wrote: Software firewalls will often simply refuse incoming connections. The basic protection of the garden-variety home router comes from network address translation (NAT), in which case TCP connections initiated from the inside will generally work, regardless of port, and incoming connections will fail. Ok, I think I'm getting the picture here. So this means that in most circumstances where the data flow from the server is frequent the client initiates the connection, usually requests some initial data and keeps polling the server periodically, issuing new requests. In this context can the client simply keep the connection alive and listen for new data from the server coming at any time rather than actively issuing requests? Are there drawbacks to this strategy? I.e. is there a limit to the number of simultaneous connections a server can keep alive? I've noticed that the socket pages mention a 5 connections limit. Is that it? What if I want to make a virtual room with 20 people connected simultaneously? I've done some network programming not much. I think if you need to receive update from a server frequently a constant connection would be better than connect-request-disconnect. As for the backlog (5), this doesn't mean that you can only have a maximum of 5 established connections. Each established connection gets a new socket object. But what I think it means is that during the listen for an incoming connection on the listening socket, if multiple connection attempts are coming in at one time it can keep a backlog of up to 5 of these connection attempts for that individual socket. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Re: How to initialize a class variable once
[EMAIL PROTECTED] wrote: Unless you are calling reload() on the module, it will only ever get _loaded_ once. Each additional import will just yield the existing module. Perhaps if you post an example of the behavior that leads you to believe that the class variables are getting reinitialized I can provide more useful help. Matt -- http://mail.python.org/mailman/listinfo/python-list There is one situation where a module can be imported/executed twice, if it is the __main__ module. Obviously the example below would be considered bad Python practice but it just shows how it can be done: main.py: class Blah(object): def action(self): print action print import if __name__ == __main__: import app app.run() app.py: def run(): import main blah = main.Blah() blah.action() python main.py: import import action The reason is the first time main.py gets loaded, it is known as '__main__' but when app imports main, it is not in sys.modules so it loads 'main.py' again but this time as 'main' Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
Python idea/proposal to assist in single-archive python applications
Python Community
The following is just an idea that I considered that may be helpful in
creating an application in a single archive easier and with less code.
Such an application would be similar to jar files for Java.
First, the application and all data files should be able to run either
extracted or zipped up into an archive. When running an application as
part of an archive, the first step Python would do would be to insert
that archive into sys.path, and then load the internal file of the same
name as the __main__ module.
This zip file:
myapp.zip
|
|-- myapp.py
|-- myapp.pyc (optional)
|-- application/ (main application package)
|-- pixmaps/
|-- ...
Could be run as something like:
python --par myapp.zip
In addition it is needed to be able to open a file just as easily
whether that file is in the archive or not. Assuming that a datafile in
an application may be located relative to the '__file__' attributes, the
following will not work in an archive:
file = open(os.path.join(os.path.dirname('__file__'), '..', 'pixmaps',
'splash.png'))
However, a simple function, perhaps built-in, could be provided which
would work for reading either internal files or regular files. That is,
the function would be able to open a file '/path/to/file', and it would
also be able to open a file '/path/to/zipfile.zip/internal/file'. If
built in the function could also take advantage of the open modes 'rb',
'rt' and 'rU'.
Currently this is not so easy. First it would require the user writing
a function to be able to open a file internally and externally just as
easily, using zipfile and StringIO for any internal files. Secondly,
opening a file in such a way only allows binary opens, it can't take
advantage of pythons 'rU' open mode if the application so needs. Also,
it still requires an external startup script to set the path and import
the internal module.
If this function was provided in Python, then and application could
fairly easily run just as well zipped up as they would unzipped.
Brian Vanderburg II
--
http://mail.python.org/mailman/listinfo/python-list
Re: Python idea/proposal to assist in single-archive python applications
[EMAIL PROTECTED] wrote: Why not use pkgutil.get_data()? Provided you remember to put your zip file on PYTHONPATH you can already run modules directly out of a zipfile (Python 2.5 and later).If your zipfile contains __main__.py then with Python 2.6 or later you can run it directly: just specify the zip filename on the command line. I'm not sure what, if anything, you are asking for that doesn't already exist in Python. -- http://mail.python.org/mailman/listinfo/python-list I wasn't aware of __main__.py for Python 2.6, I think this will work for my needs. I'll look into using pkgutil for for loading data from the archive. Thanks. Brian Vanderburg II -- http://mail.python.org/mailman/listinfo/python-list
