Re: Timestamps for TCP packets?
On Oct 2, 2009, at 12:03 AM, Thomas Johnson wrote: Is there any way to get kernel-level timestamps for TCP packets while still using the standard python sockets library for communication? I need to communicate over a TCP connection as easily as possible, but also record the timestamps of the incoming and outgoing timestamps at microsecond or nanosecond resolution. The sockets library is of course great for the communication, and I've seen some python libraries that do packet sniffing and record timestamps, but it's not clear that I can do both at the same time. Have you tried it? I don't know of any reason that using sockets and doing a packet capture would interfere with each other. What are you trying to accomplish with the packet sniffing, though? -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: weak reference to bound method
On Oct 2, 2009, at 1:54 AM, Ole Streicher wrote: I am trying to use a weak reference to a bound method: class MyClass(object): def myfunc(self): pass o = MyClass() print o.myfunc bound method MyClass.myfunc of __main__.MyClass object at 0xc675d0 import weakref r = weakref.ref(o.myfunc) print r() None This is what I do not understand. The object o is still alive, and therefore the bound method o.myfunc shall exists. Like Peter said, bound methods are created on demand when they are obtained from the instance, not when the instance is created. Why does the weak reference claim that it is removed? And how can I hold the reference to the method until the object is removed? You could combine unbound methods with a weakref to the object: r = weakref.ref(o) MyClass.myfunc(r()) You could also create a wrapper object that holds a weak reference to the instance and creates a bound method on demand: class WeakMethod(object): def __init__(self, bound_method): self.im_func = bound_method.im_func self.im_self = weakref.ref(bound_method.im_self) self.im_class = bound_method.im_class def __call__(self): obj = self.im_self() if obj is None: return None return types.MethodType(self.im_func, obj, self.im_class) # could alternately act like a callableproxy -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Are min() and max() thread-safe?
On Sep 16, 2009, at 10:39 PM, Steven D'Aprano wrote: On Wed, 16 Sep 2009 22:08:40 -0700, Miles Kaufmann wrote: On Sep 16, 2009, at 9:33 PM, Steven D'Aprano wrote: I have two threads, one running min() and the other running max() over the same list. I'm getting some mysterious results which I'm having trouble debugging. Are min() and max() thread-safe, or am I doing something fundamentally silly by having them walk over the same list simultaneously? min() and max() don't release the GIL, so yes, they are safe, and shouldn't see a list in an inconsistent state (with regard to the Python interpreter, but not necessarily to your application). But a threaded approach is somewhat silly, since the GIL ensures that they *won't* walk over the same list simultaneously (two separate lists, for that matter). Perhaps that's true for list contents which are built-ins like ints, but with custom objects, I can demonstrate that the two threads operate simultaneously at least sometimes. Unless I'm misinterpreting what I'm seeing. Whoops, sorry. Yes, if you use Python functions (or C functions that release the GIL) for the object comparison methods, a custom key function, or the sequence iterator's methods, then the the min()/max() calls could overlap between threads. If you have additional threads that could modify the list, you should synchronize access to it; if any of the earlier-mentioned functions modify the list, you're likely to get mysterious (or at least potentially unexpected) results even in a single-threaded context. On Sep 16, 2009, at 10:41 PM, Niklas Norrthon wrote: For one time sequences like files and generators your code is broken for obvious reasons. s/sequence/iterable/ -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Are min() and max() thread-safe?
On Sep 16, 2009, at 9:33 PM, Steven D'Aprano wrote: I have two threads, one running min() and the other running max() over the same list. I'm getting some mysterious results which I'm having trouble debugging. Are min() and max() thread-safe, or am I doing something fundamentally silly by having them walk over the same list simultaneously? See for yourself: http://svn.python.org/view/python/trunk/Python/bltinmodule.c?view=markup min() and max() don't release the GIL, so yes, they are safe, and shouldn't see a list in an inconsistent state (with regard to the Python interpreter, but not necessarily to your application). But a threaded approach is somewhat silly, since the GIL ensures that they *won't* walk over the same list simultaneously (two separate lists, for that matter). -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: (A Possible Solution) Re: preferred way to set encoding for print
On Sep 16, 2009, at 12:39 PM, ~flow wrote: so: how can i tell python, in a configuration or using a setting in sitecustomize.py, or similar, to use utf-8 as a default encoding? [snip Stdout_writer_with_ncrs solution] This should work: sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding=sys.stdout.encoding, errors='xmlcharrefreplace') http://mail.python.org/pipermail/python-list/2009-August/725100.html -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Why indentation is use to denote block of code?
On Sep 13, 2009, at 5:38 PM, AggieDan04 wrote: On Sep 13, 6:27 pm, Steven D'Aprano wrote: On Sun, 13 Sep 2009 15:15:40 -0700, Chris Rebert wrote: In fact it's pretty much impossible to automatically indent Python code that has had its indentation removed; it's impossible to know for sure where the dedents should occur. Just like most other syntactic elements -- if you remove all the return statements from Python code, or dot operators, it's impossible to automatically add them back in. The only difference is that some (badly written?) applications mangle leading whitespace, but very few feel free to remove other text on a whim. I don't recall actually using a mail client or newsreader that removes leading whitespace when posting, but I've occasionally seen posts from others with all indentation removed, so presumably such badly-behaved applications do exist. I haven't seen it in a mail client, but it's very common in internet forums. If you regularly deal with some sort of transport that messes with your leading whitespace, you may find Tools/scripts/pindent.py in the Python source distribution useful; it adds comments that act as block closers to your code, and can then use those comments to restore the correct indentation to a mangled version. (Most forums offer some sort of whitespace-preserving [code] tag, though; and pindent is relatively old, and apparently not well maintained (no support for with blocks)). -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: list as an instance attribute
On Sep 14, 2009, at 1:55 AM, Robin Becker wrote: Bruno Desthuilliers wrote: pep08 : class names should be Capitalized. Also, if you're using Python 2.x, make it: class Primitive(object): #... ... I find it remarkable that the most primitive classes appear to break the pep08 convention eg object, str, list etc etc. In fact all such conventions appear to be broken more often than not. So the rule appears to be create a convention and then break it :) More like break a convention and then create it. :) Before Python 2.2, built-in types were not classes at all; they couldn't be instantiated directly (from Python code), so you had to call the str() function to create an object of type string. I think there may have been some discussion of renaming the built-ins to match PEP 8 for Python 3, but if so I doubt it got very far. -Miles -- http://mail.python.org/mailman/listinfo/python-list
[issue5468] urlencode does not handle bytes, and could easily handle alternate encodings
Changes by Miles Kaufmann mile...@umich.edu: Removed file: http://bugs.python.org/file14796/urllib_parse.py3k.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue5468 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Re: Why does this group have so much spam?
casebash walkr...@gmail.com wrote in message news:7294bf8b-9819-4b6d-92b2- afc1c8042...@x6g2000prc.googlegroups.com... So much of it could be removed even by simple keyword filtering. Funny, I was just thinking recently about how *little* spam this list gets--on the other hand, I'm following it via the python-list@ mailing list. The list owners do a great job of keeping the level of spam at a minimum, though there are occasional false positives (like your post, apparently, since I'm only seeing the replies). -Miles -- http://mail.python.org/mailman/listinfo/python-list
[issue5468] urlencode does not handle bytes, and could easily handle alternate encodings
Miles Kaufmann mile...@umich.edu added the comment: I've attached a patch that provides similar functionality to Dan Mahn's urlencode(), as well as providing encoding and errors parameters to parse_qs and parse_qsl, updating the documentation to reflect the added parameters, and adding test cases. The implementation of urlencode() is not the same as dmahn's, and has a more straightforward control flow and less code duplication than the current implementation. (For the tests, I tried to match the style of the file I was adding to with regard to (expect, result) order, which is why it's inconsistent.) -- keywords: +patch versions: +Python 3.2 Added file: http://bugs.python.org/file14796/urllib_parse.py3k.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue5468 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Re: Need help with Python scoping rules
On Aug 26, 2009, at 1:11 PM, kj wrote: I think I understand the answers well enough. What I *really* don't understand is why this particular feature of Python (i.e. that functions defined within a class statement are forbidden from seeing other identifiers defined within the class statement) is generally considered to be perfectly OK. IMO it's a bizarre, inexplicable blindspot (which, among other things, gives rise to a certain worry about what other similar craziness lurks under Python's image of rationality). I have never seen even a half-hearted justification, from a language design point of view, for why this particular feature is worth having. Guido's design justifications: http://mail.python.org/pipermail/python-dev/2000-November/010598.html -- My personal justification: Python has used the same basic method of class creation since the very beginning: create a new local namespace, execute the class suite in that namespace, and then create a class, using the contents of the namespace as the class attributes. The important thing to note here is that there are really *two* namespaces--the local namespace that exists while the class suite is being executed (what I call the suite namespace), and the namespace of the class itself--and the first ceases to exist when the second is created. The two namespaces generally contain the same names at the point that the transfer occurs, but they don't have to; the metaclass (which constructs the class) is free to mess with the dictionary of attributes before creating the class. Suppose for a moment that the suite namespace *were* visible to nested scopes. The simplest and most consistent implementation would be to have a closure generated by a class statement be similar to that generated by a function--i.e., the closure would be over the suite namespace. This hardly seems desirable, though, because the suite namespace and the class namespace would get out of sync when different objects were assigned to the class namespace: class C: x = 1 def foo(self): print x print self.x o = C() o.foo() 1 1 o.x = 2 o.foo() 1 2 Surely such an implementation would be considered an even larger Python wart then not having the suite namespace visible to nested scopes at all. But it's better than the alternative of trying to unify the class suite namespace and the class namespace, which would be a nightmare of special cases (adding/deleting class attributes? descriptors? __getattr__?) and require an implementation completely separate from that of normal nested scopes. -Miles P.S. Just for fun: import types def make_class(*bases): Decorator to allow you to (ab)use a function as a class definition. The function must take no arguments and end with 'return locals()'; bases are (optionally) specified as arguments to make_class; metaclasses other than 'type' are not supported. @make_class ... def C(): ... greeting = 'Hello' ... target = 'world' ... def greet(self): ... print '%s, %s' % (self.greeting, target) ... return locals() ... C().greet() Hello, world def decorator(func): return type(func.func_name, bases, func()) if len(bases) == 1 and isinstance(bases[0], types.FunctionType): func = bases[0] bases = (object,) return decorator(func) if not bases: bases = (object,) return decorator -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help with Python scoping rules
On Aug 27, 2009, at 4:49 PM, kj wrote: Miles Kaufmann mile...@umich.edu writes: Guido's design justifications: http://mail.python.org/pipermail/python-dev/2000-November/010598.html Ah! Clarity! Thanks! How did you find this? Did you know of this post already? Or is there some special way to search Guido's design justifications? I just checked the python-dev archives around the time that PEP 227 was written. ...because the suite namespace and the class namespace would get out of sync when different objects were assigned to the class namespace: class C: x = 1 def foo(self): print x print self.x o = C() o.foo() 1 1 o.x = 2 o.foo() 1 2 But this unfortunate situation is already possible, because one can already define class C: x = 1 def foo(self): print C.x print self.x which would lead to exactly the same thing. You're right, of course. If I had been thinking properly, I would have posted this: ... the suite namespace and the class namespace would get out of sync when different objects were assigned to the class namespace: # In a hypothetical Python with nested class suite scoping: class C: x = 1 @classmethod def foo(cls): print x print cls.x C.foo() 1 1 C.x = 2 C.foo() 1 2 With your example, the result is at least easily explainable: self.x is originally 1 because the object namespace inherits from the class namespace, but running 'o.x = 2' rebinds 'x' in the object namespace (without affecting the class namespace). It's a distinction that sometimes trips up newbies (and me, apparently ;) ), but it's straightforward to comprehend once explained. But the distinction between the class suite namespace and the class namespace is far more subtle; extending the lifetime of the first so that it still exists after the second is created is, IMO, asking for trouble (and trying to unify the two double so). -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Waiting for a subprocess to exit
On Aug 20, 2009, at 10:13 PM, Ben Finney wrote: The module documentation has a section on replacing ‘os.system’ http://docs.python.org/library/subprocess#replacing-os-system, which says to use:: process = subprocess.Popen(mycmd + myarg, shell=True) status = os.waitpid(process.pid, 0) But a ‘Popen’ instance has its own ‘wait’ method, which waits for exit URL:http://docs.python.org/library/subprocess#subprocess.Popen.wait. Why would I use ‘os.waitpid’ instead of:: process = subprocess.Popen(mycmd + myarg, shell=True) process.wait() status = process.returncode Really, you can just use: process = subprocess.Popen(mycmd + myarg, shell=True) status = process.wait() I'm not sure why the documentation suggests using os.waitpid. I would recommend avoiding shell=True whenever possible. It's used in the examples, I suspect, to ease the transition from the functions being replaced, but all it takes is for a filename or some other input to unexpectedly contain whitespace or a metacharacter and your script will stop working--or worse, do damage (cf. the iTunes 2 installer debacle[1]). Leaving shell=False makes scripts more secure and robust; besides, when I'm putting together a command and its arguments, it's as convenient to build a list (['mycmd', 'myarg']) as it is a string (if not more so). -Miles [1]: http://apple.slashdot.org/article.pl?sid=01/11/04/0412209#comment_2518563 -- http://mail.python.org/mailman/listinfo/python-list
Re: Object Reference question
On Aug 20, 2009, at 11:07 PM, josef wrote:
To begin, I'm new with python. I've read a few discussions about
object references and I think I understand them.
To be clear, Python uses a Pass By Object Reference model.
x = 1
x becomes the object reference, while an object is created with the
type 'int', value 1, and identifier (id(x)). Doing this with a class,
x = myclass(), does the same thing, but with more or less object
attributes. Every object has a type and an identifier (id()),
according to the Python Language Reference for 2.6.2 section 3.1.
x in both cases is the object reference. I would like to use the
object to refer to the object reference.
Stop right there. 'x' is not *the* object reference. It is *an*
object reference (or in my preferred terminology, a label). Suppose
you do:
x = myclass()
y = x
The labels 'x' and 'y' both refer to the same object with equal
precedence. There is no mapping from object back to label; it is a
one-way pointer. Also importantly, labels themselves are not objects,
and cannot be accessed or referred to.
(This is a slight oversimplification; thanks to Python's reflection
and introspection capabilities, it is possible to access labels to
some extent, and in some limited situations it is possible to use
stack inspection to obtain a label for an object. But this is hackish
and error-prone, and should never be used when a more Pythonic method
is available.)
The following is what I would like to do:
I have a list of class instances dk = [ a, b, c, d ], where a, b, c, d
is an object reference. Entering dk gives me the object: [MyClass0
instance at 0x, MyClass1 instance at 0x0008, MyClass2 instance at
0x0010 ... ]
I need the object reference name (a,b,c,d) from dk to use as input for
a file.
It sounds like you should either be storing that name as an attribute
of the object, or using a dictionary ({'a': a, 'b': b, ...}).
-Miles
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Re: Skipping a superclass
On Aug 2, 2009, at 5:36 AM, Steven D'Aprano wrote: I have a series of subclasses like this: class A(object): def method(self, *args): print Lots of work gets done here in the base class class B(A): def method(self, *args): print A little bit of work gets done in B super(B, self).method(*args) class C(B): def method(self, *args): print A little bit of work gets done in C super(C, self).method(*args) However, the work done in C.method() makes the work done in B.method() obsolete: I want one to run, or the other, but not both. C does need to inherit from B, for the sake of the other methods, so I want C.method() *only* to skip B while still inheriting from A. (All other methods have to inherit from B as normal.) This might not be applicable to the larger problem you're trying to solve, but for this sample, I would write it as: class A(object): def method(self, *args): self._method(*args) print Lots of work gets done here in the base class def _method(self, *args): pass # or perhaps raise NotImplemented class B(A): def _method(self, *args): print A little bit of work gets done in B class C(B): def _method(self, *args): print A little bit of work gets done in C So what I have done is change the call to super in C to super(B, self) instead of super(C, self). It seems to work, but is this safe to do? Or are there strange side-effects I haven't seen yet? In a diamond-inheritance situation, you may end up skipping methods besides just B.method(). -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: python 3 and stringio.seek
On Jul 28, 2009, at 6:30 AM, Michele Petrazzo wrote:
Hi list,
I'm trying to port a my library to python 3, but I have a problem
with a
the stringio.seek:
the method not accept anymore a value like pos=-6 mode=1, but the
old
(2.X) version yes...
The error:
File /home/devel/Py3/lib/python3.0/io.py, line 2031, in seek
return self._seek(pos, whence)
IOError: Can't do nonzero cur-relative seeks
How solve this?
In Python 2, StringIO is a stream of bytes (non-Unicode characters).
In Python 3, StringIO is a stream of text (Unicode characters). In
the early development of Python 3 (and 3.1's _pyio), it was
implemented as a TextIOWrapper over a BytesIO buffer. TextIOWrapper
does not support relative seeks because it is difficult to map the
concept of a current position between bytes and the text that it
encodes, especially with variable-width encodings and other
considerations. Furthermore, the value returned from
TextIOWrapper.tell isn't just a file position but a cookie that
contains other data necessary to restore the decoding mechanism to the
same state. However, for the default encoding (utf-8), the current
position is equivalent to that of the underlying bytes buffer.
In Python 3, StringIO is implemented using an internal buffer of
Unicode characters. There is no technical reason why it can't support
relative seeks; I assume it does not for compatibility with the
original Python TextIOWrapper implementation (which is present in
3.1's _pyio, but not in 3.0).
Note that because of the different implementations, StringIO.tell()
(and seek) behaves differently for the C and Python implementations:
$ python3.1
import io, _pyio
s = io.StringIO('\u263A'); s.read(1), s.tell()
('☺', 1)
s = _pyio.StringIO('\u263A'); s.read(1), s.tell()
('☺', 3)
The end result seems to be that, for text streams (including
StreamIO), you *should* treat the value returned by tell() as an
opaque magic cookie, and *only* pass values to seek() that you have
obtained from a previous tell() call. However, in practice, it
appears that you *may* seek StringIO objects relatively by characters
using s.seek(s.tell() + n), so long as you do not use the
_pyio.StringIO implementation.
If what you actually want is a stream of bytes, use BytesIO, which may
be seeked (sought?) however you please.
I'm basing this all on my reading of the Python source (and svn
history), since it doesn't seem to be documented, so take it with a
grain of salt.
-Miles
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Re: trouble with minidom
On Jul 21, 2009, at 8:08 PM, Ronn Ross wrote:
Hello I'm trying to read an xml file using minidome. The xml looks
like:
rootNode
project
namemyProj/name
path/here//path
/project
/rootNode
My code looks like so:
from xml.dom.minidom import parse
dom = parse(myfile.xml)
for node in dom.getElementsByTagName(project'):
print('name: %s, path: %s \n') % (node.childNodes[0].nodeValue,
node.childNodes[1])
Unfortunately, it returns 'nodeValue as none. I'm trying to read the
value out of the node fir example name: myProj. I haven't found much
help in the documentation. Can someone point me in the right
direction?
Two issues:
In your example XML file, the first child node of the project Element
is the Text node containing the whitespace between the project and
name tags. node.childNodes[0] will select that whitespace node.
The nodeValue of an Element is null (None). In order to get the text
contents of an element, you must get the nodeValue of the Text child
node of the Element.
Like Gabriel, I would recommend using an XML library with a more
concise API than the W3C DOM (I like lxml.objectify). But if you
stick with xml.dom, use the specification as a reference:
http://www.w3.org/TR/REC-DOM-Level-1/
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Re: Why not enforce four space indentations in version 3.x?
On Jul 15, 2009, at 4:26 PM, David Bolen wrote: Miles Kaufmann mile...@umich.edu writes: On Jul 14, 2009, at 5:06 PM, David Bolen wrote: Are you sure? It seems to restrict them in the same block, but not in the entire file. At least I was able to use both space and tab indented blocks in the same file with Python 3.0 and 3.1. It seems to me that, within an indented block, Python 3.1 requires that you are consistent in your use of indentation characters *for that indentation level*. For example, the following code seems to be allowed: Um, right - in other words, what I said :-) I wasn't trying to correct you, just being more explicit. :) After reading your post, I still wasn't sure if the restriction on mixing spaces and tabs applied to nested blocks--I was surprised that the code sample I included was allowed. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: missing 'xor' Boolean operator
On Jul 15, 2009, at 1:43 PM, Jean-Michel Pichavant wrote:
Hrvoje Niksic wrote:
[snip]
Note that in Python A or B is in fact not equivalent to not(not A and
not B).
l = [(True, True), (True, False), (False, True), (False, False)]
for p in l:
... p[0] or p[1]
[snip]
Did I make twice the same obvious error ?
Try again with:
l = [('foo','bar'), ('foo', ''), ('', 'bar'), ('', '')]
-Miles
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Re: missing 'xor' Boolean operator
On Jul 15, 2009, at 1:55 PM, Emile van Sebille wrote: On 7/15/2009 10:43 AM Jean-Michel Pichavant said... Hrvoje Niksic wrote: [snip] Note that in Python A or B is in fact not equivalent to not(not A and not B). Did I make twice the same obvious error ? No -- but in the not(not... example it doesn't short-circuit. No; like 'A or B', 'not (not A and not B)' does in fact short-circuit if A is True. (The 'and' condition does not have to evaluate the right operand when 'not A' is False.) -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: python first assignment of a global variable
On Jul 15, 2009, at 1:55 PM, Rodrigue wrote: Basically, I was very surprised to discover that e() raises an exception, but even more that e_raise() points to if not MY_GLOBAL Is the problem not really when I assign? My assumption is that some reordering is happening behind the scenes that creates a situation similar to the += which assigns hence expects to be at the local level. The determination of whether a name is a reference to a local or global variable is made at compile time. When a function contains a single assignment (or augmented assignment) to a name, the compiler generates bytecode such that all references to that name within the function will be looked up in the local scope only, including those before the assignment statement. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Why not enforce four space indentations in version 3.x?
On Jul 14, 2009, at 5:06 PM, David Bolen wrote: Are you sure? It seems to restrict them in the same block, but not in the entire file. At least I was able to use both space and tab indented blocks in the same file with Python 3.0 and 3.1. It seems to me that, within an indented block, Python 3.1 requires that you are consistent in your use of indentation characters *for that indentation level*. For example, the following code seems to be allowed: def foo(): TABif True: TABSPSPx = 1 TABelse: TABTABx = 2 TABreturn x But replacing any of the first tabs on each line with 8 spaces (without replacing them all), which previously would have been allowed, is now an error. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: missing 'xor' Boolean operator
On Jul 15, 2009, at 12:07 AM, Dr. Phillip M. Feldman wrote: I appreciate the effort that people have made, but I'm not impressed with any of the answers. For one thing, xor should be able to accept an arbitrary number of input arguments (not just two) You originally proposed this in the context of the existing short- circuit boolean operators. Those operators (being infix) take only two operands. and should return True if and only if the number of input arguments that evaluate to True is odd The existing and/or operators always return the value of one of the operands--not necessarily True or False--which is another important property, but one that can't be translated fully to xor. Given the lack of context in your original post, hopefully you'll forgive me being unimpressed by your not being impressed. :) Here's my code: def xor(*args): xor accepts an arbitrary number of input arguments, returning True if and only if bool() evaluates to True for an odd number of the input arguments. result= False for arg in args: if bool(arg): result= not result return result If all you want is a True or False result, I'd write it like this: import operator def xor(*args): return reduce(operator.xor, map(bool, args)) # or imap In order to make it act more like the other logical operators, I'd use MRAB's 2-argument xor as the reducer--though I can't really see the utility. def xor2(a, b): return (not b and a) or (not a and b) def xor(*args): return reduce(xor2, args) You may also find this question interesting: http://stackoverflow.com/questions/432842/ -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Catching control-C
On Jul 9, 2009, at 9:20 AM, Lie Ryan wrote: Michael Mossey wrote: I want to understand better what the secret is to responding to a ctrl-C in any shape or form. Are you asking: when would the python interpreter process KeyboardInterrupt? ... In single threaded python program, the currently running thread is always the main thread (which can handle KeyboardInterrupt). I believe SIGINT is checked at every ticks. But SIGINT cannot interrupt atomic operations (i.e. it cannot interrupt long operations that takes a single tick). Some otherwise atomic single-bytecode operations (like large integer arithmetic) do manual checks for whether signals were raised (though that won't help at all if the operation isn't on the main thread). I believe a tick in python is equivalent to a single bytecode, but please correct me if I'm wrong. Not all opcodes qualify as a tick. In general, those opcodes that cause control to remain in the eval loop (and not make calls to other Python or C functions) don't qualify as ticks (but there are exceptions, e.g. so that while True: pass is interruptible). In Python/ceval.c: PyEval_EvalFrameEx(), those opcodes that don't end in goto fast_next_opcode are ticks. Please correct me if _I'm_ wrong! :) -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: function local namespace question
On Jul 8, 2009, at 1:35 PM, Paul LaFollette wrote: I cannot figure out any way to get a hook into the local namespace of a user defined function. I have tried making a wrapper class that grabs the function call and then uses exec to invoke myfunction.__code__ with my own dictionaries. This runs the (no argument) function properly (losing the return value, but I can deal with that) but never accesses the local logging dictionary that I specify in the exec() call. Perhaps the local namespace of a function is not a dict at all? Right. Within functions, local variable name accesses and assignments are compiled into bytecode instructions (LOAD_FAST, STORE_FAST) that manipulate pointers to objects by indexing directly into a C array in the frame. The locals dictionary of a frame is generated on-demand from that array when accessed. There is no way that I'm aware of to directly hook into function namespace access and manipulation. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Passing parameters for a C program in Linux.
On Jun 30, 2009, at 6:46 AM, venutaurus...@gmail.com wrote: I have to write an automted script which will test my c program. That program when run will ask for the commands. Keep in mind that, if your test script checks the program's output before giving it input, you can run into problems with buffering. The standard C library uses line-based buffering when a program is using a terminal for output, but when it's outputting to a pipe it uses block buffering. This can be a problem when running a process using subprocess--your program will buffer the prompt, and your test script won't see it, so the test will deadlock. The problem can also exist in the opposite direction. Possible solutions: - Explicitly set both your test script and your program to have line- buffered output. - Add a flush statement whenever you finish writing output and expect input. - Use pexpect, which uses a pseudo-tty and will make C stdio default to line buffering. - Use pdpi's solution, which, since it doesn't wait for a prompt before supplying input, doesn't have this issue. -- http://mail.python.org/mailman/listinfo/python-list
Re: Regular Expression Non Capturing Grouping Does Not Work.
On Jun 27, 2009, at 3:28 AM, Virtual Buddha wrote: Hello all, I am having some difficulties with the non-capturing grouping in python regular expression module. Even the code from the online documentation (http://docs.python.org/ howto/regex.html#non-capturing-and-named-groups) does not seem to work. ... Notice that you are calling .group() on the match object instead of .groups(). Without any arguments, .group() is equivalent to .group(0), which means return the entire matching string. http://docs.python.org/library/re.html#re.MatchObject.group -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: No trees in the stdlib?
João Valverde wrote: To answer the question of what I need the BSTs for, without getting into too many boring details it is to merge and sort IP blocklists, that is, large datasets of ranges in the form of (IP address, IP address, string). Originally I was also serializing them in a binary format (but no more after a redesign). I kept the merge and sort part as a helper script, but that is considerably simpler to implement. ... As an anecdotal data point (honestly not trying to raise the Python is slow strawman), I implemented the same algorithm in C and Python, using pyavl. Round numbers were 4 mins vs 4 seconds, against Python (plus pyavl). Even considering I'm a worse Python programmer than C programmer, it's a lot. I know many will probably think I tried to do C in Python but that's not the case, at least I don' t think so. Anyway like I said, not really relevant to this discussion. What format were you using to represent the IP addresses? (Is it a Python class?) And why wouldn't you use a network address/subnet mask pair to represent block ranges? (It seems like being able to represent ranges that don't fit into a subnet's 2^n block wouldn't be that common of an occurrence, and that it might be more useful to make those ranges easier to manipulate.) One of the major disadvantages of using a tree container is that usually multiple comparisons must be done for every tree operation. When that comparison involves a call into Python bytecode (for custom cmp/lt methods) the cost can be substantial. Compare that to Python's hash-based containers, which only need to call comparison methods in the event of hash collisions (and that's hash collisions, not hash table bucket collisions, since the containers cache each object's hash value). I would imagine that tree-based containers would only be worth using with objects with comparison methods implemented in C. Not that I'm trying to be an apologist, or reject your arguments; I can definitely see the use case for a well-implemented, fast tree- based container for Python. And so much the better if, when you need one, there was a clear consensus about what package to use (like PIL for image manipulation--it won't meet every need, and there are others out there, but it's usually the first recommended), rather than having to search out and evaluate a dozen different ones. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: No trees in the stdlib?
On Jun 26, 2009, at 2:23 AM, Chris Rebert wrote: On Thu, Jun 25, 2009 at 10:55 PM, João Valverdebacku...@netcabo.pt wrote: Aahz wrote: In article mailman.2139.1245994218.8015.python-l...@python.org, Tom Reed tomree...@gmail.com wrote: Why no trees in the standard library, if not as a built in? I searched the archive but couldn't find a relevant discussion. Seems like a glaring omission considering the batteries included philosophy, particularly balanced binary search trees. No interest, no good implementations, something other reason? Seems like a good fit for the collections module. Can anyone shed some light? What do you want such a tree for? Why are dicts and the bisect module inadequate? Note that there are plenty of different tree implementations available from either PyPI or the Cookbook. Simple example usage case: Insert string into data structure in sorted order if it doesn't exist, else retrieve it. That's pretty much the bisect module in a nutshell. It manipulates a sorted list using binary search. With O(n) insertions and removals, though. A decent self-balancing binary tree will generally do those in O(log n). -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: urllib2.urlopen issue
On Jun 24, 2009, at 2:59 PM, David wrote: On Jun 24, 11:27 am, Chris Rebert wrote: On Wed, Jun 24, 2009 at 10:50 AM, David wrote: hello, I have a url that is http://query.directrdr.com/ptrack? pid=225v_url=http:// www.plentyoffish.comkeyword=flowersfeed=1ip=12.2.2.2said=$said. If I open it on a browser, I can get its contents without any problem. However, if I use following code, import urllib2 url = 'http://query.directrdr.com/ptrack?pid=225v_url=http:// www.plentyoffish.comkeyword=flowersfeed=1ip=12.2.2.2said=$said' xml = urllib2.urlopen(url).read() then I get an exception of File /usr/lib/python2.5/urllib2.py, line 1082, in do_open raise URLError(err) urllib2.URLError: urlopen error (-2, 'Name or service not known') Unable to reproduce with either urllib or urllib2's urlopen(). I get some XML back without error both ways. Using Python 2.6.2 on Mac OS X. Thanks Aahz. And thanks Chris. The XML content is what I am looking for. I use Python 2.5. Maybe I should update to 2.6.2? Python version problem? No, it also works for me on Python 2.5.1. A wild guess: does this code work? import socket socket.gethostbyname(socket.gethostname()) If it throws a similar exception (Name or service not known), the root problem may be a misconfiguration in your /etc/hosts or /etc/ resolv.conf files. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: [Mac] file copy
On Jun 23, 2009, at 9:52 AM, Tobias Weber wrote: Hi, which is the best way to copy files on OS X? I want to preserve resource forks and extended attributes. ... bin/cp -p This. cp -p, mv, rsync -E, tar, and other utilities will use the copyfile(3) API to preserve extended attributes, resource forks, and ACLs. cp -Rp should be just as safe as a Finder copy--moreso if you run it as root--with the exception of preserving creation dates. Or if you're worried about hard links, check out ditto(1). You presumably already know this, but avoid shutil at all costs. BackupBouncer (http://www.n8gray.org/code/backup-bouncer/) makes testing what gets preserved by various methods of copying quick and easy. The results for a Finder copy: Verifying:basic-permissions ... FAIL (Critical) Verifying: timestamps ... ok (Critical) Verifying: symlinks ... ok (Critical) Verifying:symlink-ownership ... FAIL Verifying:hardlinks ... FAIL (Important) Verifying: resource-forks ... Sub-test: on files ... ok (Critical) Sub-test: on hardlinked files ... FAIL (Important) Verifying: finder-flags ... ok (Critical) Verifying: finder-locks ... ok Verifying:creation-date ... ok Verifying:bsd-flags ... ok Verifying: extended-attrs ... Sub-test: on files ... ok (Important) Sub-test: on directories ... ok (Important) Sub-test: on symlinks ... ok Verifying: access-control-lists ... Sub-test: on files ... ok (Important) Sub-test: on dirs ... ok (Important) Verifying: fifo ... FAIL Verifying: devices ... FAIL Verifying: combo-tests ... Sub-test: xattrs + rsrc forks ... ok Sub-test: lots of metadata ... FAIL sudo cp -Rp: Verifying:basic-permissions ... ok (Critical) Verifying: timestamps ... ok (Critical) Verifying: symlinks ... ok (Critical) Verifying:symlink-ownership ... ok Verifying:hardlinks ... FAIL (Important) Verifying: resource-forks ... Sub-test: on files ... ok (Critical) Sub-test: on hardlinked files ... FAIL (Important) Verifying: finder-flags ... ok (Critical) Verifying: finder-locks ... ok Verifying:creation-date ... FAIL Verifying:bsd-flags ... ok Verifying: extended-attrs ... Sub-test: on files ... ok (Important) Sub-test: on directories ... ok (Important) Sub-test: on symlinks ... ok Verifying: access-control-lists ... Sub-test: on files ... ok (Important) Sub-test: on dirs ... ok (Important) Verifying: fifo ... ok Verifying: devices ... ok Verifying: combo-tests ... Sub-test: xattrs + rsrc forks ... ok Sub-test: lots of metadata ... ok -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: urllib2 content-type headers
On Jun 21, 2009, at 12:01 PM, TYR wrote: Unfortunately, I'm getting nothing but 400 Bad Requests. I suspect this is due to an unfeature of urllib2. Notably, although you can use urllib2.Request's add_header method to append a header, the documentation (http://docs.python.org/library/urllib2.html) says that: remember that a few standard headers (Content-Length, Content-Type and Host) are added when the Request is passed to urlopen() (or OpenerDirector.open()). And: Note that there cannot be more than one header with the same name, and later calls will overwrite previous calls in case the key collides. To put it another way, you cannot rely on Content-Type being correct because whatever you set it to explicitly, urllib2 will silently change it to something else which may be wrong, and there is no way to stop it. What happened to explicit is better than implicit? Those headers are added (by AbstractHTTPHandler.do_request_) only if they are missing. -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: generator expression works in shell, NameError in script
On Jun 19, 2009, at 8:45 AM, Bruno Desthuilliers wrote: class Foo(object): ... bar = ['a', 'b', 'c'] ... baaz = list((b, b) for b in bar) but it indeed looks like using bar.index *in a generator expression* fails (at least in 2.5.2) : class Foo(object): ... bar = ['a', 'b', 'c'] ... baaz = list((bar.index(b), b) for b in bar) ... Traceback (most recent call last): File stdin, line 1, in module File stdin, line 3, in Foo File stdin, line 3, in genexpr NameError: global name 'bar' is not defined The reason that the first one works but the second fails is clearer if you translate each generator expression to the approximately equivalent generator function: class Foo(object): bar = ['a', 'b', 'c'] def _gen(_0): for b in _0: yield (b, b) baaz = list(_gen(iter(bar)) # PEP 227: the name bindings that occur in the class block # are not visible to enclosed functions class Foo(object): bar = ['a', 'b', 'c'] def _gen(_0): for b in _0: yield (bar.index(b), b) baaz = list(_gen(iter(bar)) -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: class or instance method
On Jun 21, 2009, at 5:23 PM, Scott David Daniels wrote: Hrvoje Niksic wrote: ... class class_or_instance(object): def __init__(self, fn): self.fn = fn def __get__(self, obj, cls): if obj is not None: return lambda *args, **kwds: self.fn(obj, *args, **kwds) else: return lambda *args, **kwds: self.fn(cls, *args, **kwds) ... Just to polish a bit: import functools class ClassOrInstance(object): def __init__(self, fn): self._function = fn self._wrapper = functools.wraps(fn) def __get__(self, obj, cls): return self._wrapper(functools.partial(self._function, cls if obj is None else obj)) from types import MethodType class ClassOrInstance(object): def __init__(self, func): self._func = func def __get__(self, obj, cls): return MethodType(self._func, cls if obj is None else obj, cls) -Miles -- http://mail.python.org/mailman/listinfo/python-list
[issue6234] cgi.FieldStorage is broken when given POST data
Changes by Miles Kaufmann mile...@umich.edu: -- nosy: +milesck ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6234 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue5468] urlencode does not handle bytes, and could easily handle alternate encodings
Miles Kaufmann mile...@umich.edu added the comment: parse_qs and parse_qsl should also grow encoding and errors parameters to pass to the underlying unquote(). -- nosy: +milesck ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue5468 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
Re: Function/method returning list of chars in string?
On Jun 9, 2009, at 6:05 AM, Diez B. Roggisch wrote: Also as list-comps are going away and are replaced by list(generator-expression) Where did you hear that? -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: random number including 1 - i.e. [0,1]
On Jun 9, 2009, at 7:05 PM, Mensanator wrote: On Jun 9, 4:33 pm, Esmail wrote: Hi, random.random() will generate a random value in the range [0, 1). Is there an easy way to generate random values in the range [0, 1]? I.e., including 1? I am implementing an algorithm and want to stay as true to the original design specifications as possible though I suppose the difference between the two max values might be minimal. I'm curious what algorithm calls for random numbers on a closed interval. ps: I'm confused by the docs for uniform(): random.uniform(a, b) Return a random floating point number N such that a = N = b for a = b That's wrong. Where did you get it? http://docs.python.org/library/random.html -Miles -- http://mail.python.org/mailman/listinfo/python-list
Re: Winter Madness - Passing Python objects as Strings
On Jun 4, 2009, at 3:25 AM, Hendrik van Rooyen wrote: A can is like a pickle, in that it is a string, but anything can be canned. Unlike a pickle, a can cannot leave the process, though, unless the object it points to lives in shared memory. If you have any interest, contact me and I will send you the source. Sounds like di(), which can be written: import _ctypes di = _ctypes.PyObj_FromPtr def can(o): return str(id(o)) def uncan(s): return di(int(s)) http://www.friday.com/bbum/2007/08/24/python-di/ -Miles -- http://mail.python.org/mailman/listinfo/python-list
