[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti added the comment: Attached a new patch. -- Added file: http://bugs.python.org/file28563/issue13094-2.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
R. David Murray added the comment: Looks good to me. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Roundup Robot added the comment: New changeset fdc894d44d82 by Ezio Melotti in branch '2.7': #13094: add Programming FAQ entry about the behavior of closures. http://hg.python.org/cpython/rev/fdc894d44d82 New changeset 02933454b7ce by Ezio Melotti in branch '3.2': #13094: add Programming FAQ entry about the behavior of closures. http://hg.python.org/cpython/rev/02933454b7ce New changeset 827ddaaa45e4 by Ezio Melotti in branch '3.3': #13094: merge with 3.2. http://hg.python.org/cpython/rev/827ddaaa45e4 New changeset 1bf7ae6c5324 by Ezio Melotti in branch 'default': #13094: merge with 3.3. http://hg.python.org/cpython/rev/1bf7ae6c5324 -- nosy: +python-dev ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti added the comment: Fixed, thanks for the review! -- resolution: - fixed stage: patch review - committed/rejected status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
R. David Murray added the comment: The FAQ (as in, this question gets asked again and again) is something like why do the lambdas I define in a loop all return the same result when the input value was different when each one was defined? The same applies to regular functions, but people almost never do that in a loop, so in that case they are more likely to think of the scoping issue. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti added the comment: why do the lambdas I define in a loop all return the same result when the input value was different when each one was defined? I thought about that, but that sounds a bit too long/specific. It also has the problem that the issue is not strictly related to lambdas or loops (even if this combination might be more common), and doesn't say where the result come from. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
R. David Murray added the comment: The point is, it is a FAQ. We are talking about updating the FAQ document. It doesn't matter if the text is too specific, if it is in fact a FAQ. And it is. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti added the comment: Here's a patch. -- keywords: +patch stage: needs patch - patch review Added file: http://bugs.python.org/file28550/issue13094.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Changes by Ezio Melotti ezio.melo...@gmail.com: -- assignee: - ezio.melotti ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti added the comment: I'm having some problem at deciding what the title of the FAQ should be, and what the actual problem is. ISTM that OP's problem is the same as: x = 1 def foo(): return x ... x = 2 foo() 2 except that he has 3 lambdas in a loop that get attached to an instance rather than a simple function -- but the problem is that in both cases the function references a global variable whose value is retrieved at calling time rather that being set at definition time. IOW the solution should be clear, but the code is complex enough that it's not easy to recognize the analogy with the simpler case. I'm not even sure this has anything to do with closures, unless you consider the global scope a closure. Maybe the What are the rules for local and global variables in Python? FAQ could be expanded with a few examples to cover this case too. -- assignee: ezio.melotti - nosy: +chris.jerdonek ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Changes by Ezio Melotti ezio.melo...@gmail.com: -- assignee: docs@python - ezio.melotti ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Changes by Ezio Melotti ezio.melo...@gmail.com: -- keywords: +easy stage: - needs patch type: - enhancement versions: +Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Changes by Éric Araujo mer...@netwok.org: -- assignee: - docs@python components: +Documentation -None nosy: +eric.araujo versions: +Python 3.2, Python 3.3 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Changes by R. David Murray rdmur...@bitdance.com: -- title: setattr misbehaves when used with lambdas inside for loop - Need Programming FAQ entry for the behavior of closures ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti ezio.melo...@gmail.com added the comment: To understand better what's going on, try to change the value of 'each' after the 3 prints and then call again the 3 methods: you will see that they now return the new value of each. This is because the lambdas refer to global 'each' (that at the end of the loop is set to 'baz'). If you do setattr(x, each, lambda each=each: each), the each will be local to the lambda, and it will then work as expected. An entry in the FAQ would be useful, I thought it was there already but apparently it's not (I'm pretty sure I saw this already somewhere in the doc, but I can't seem to find where). -- assignee: docs@python - components: +None -Documentation nosy: +ezio.melotti stage: needs patch - type: behavior - versions: -Python 3.2, Python 3.3 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Tomáš Dvořák dvto...@gmail.com added the comment: Thank you all very much for the super-quick responses. I'm used to smalltalk, so the python variable binding behaviour is unnatural to me, but I guess there must have been some reasons for making it behave this way. Ezio, the lambda each=each: each trick works nicely, thanks a lot. But - what does it mean? :) I just don't know how to parse and understand it :-) Best regards, Tomáš Dvořák -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue13094] Need Programming FAQ entry for the behavior of closures
Ezio Melotti ezio.melo...@gmail.com added the comment: Maybe with a different name is less confusing: lambda return_value=each: return_value This copies the value of 'each' in a variable called 'return_value' that is local to the lambda. Since the copy happens when the lambdas are defined, 'return_value' has then the right value. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue13094 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
