Hi Arnaud et al, Here is the link to the bug report from which the discussion in PEP 289 was extracted:
http://bugs.python.org/issue872326 It looks like they were fixing a bunch of bugs and that this discussion was one of the many in that thread. Here is another post which points to the core of the issue: early/late binding. It is also pointed to in PEP 289. http://mail.python.org/pipermail/python-dev/2004-April/044555.html Here is Guido's rationale (his text is the items (a) and (b) below. My comments follow. (a) I find it hard to defend automatic variable capture given Python's general late-binding semantics MY COMMENTS: That is a good point. There are however exceptions to the "general late-binding semantics" (GLBS) in Python. The outer loop does bind early in this case in fact. A point to consider along with GLBS is the unintuitive early bind of the external iterator vs late bind of the internal iterator. That is a function not of early vs. late binding, but of the current translation of generator expressions to generator functions. Using Arnaud's approach would fix that and make the code IMO so more pythonic. (b) I believe that use cases needing early binding are uncommon and strained: they all involve creating a list of generator expressions, which IMO is a pretty unusual thing to do MY COMMENTS: This is actually a pretty common use case. Any iteration over objects of arity 2 or greater (A matrix, a table, a tree searched breadthwise under some data structures, etc.) can conveniently and cleanly be expressed using a generator expression. I'd also add that perhaps the title of Guido's post: "Generator Expressions - Let's Move Forward" may have unintentionally discouraged people from reexamining the issue. I would like to see this decision revisited. Obviously before spending any time on this I'd like to gauge if there is further interest. Am I off the mark? Maybe there is a technical misunderstanding on my part. If there are more people affected (Since the last week I found some other postings here and on other lists and blogs) who can make a clear case, then what is the next step? Cheers, Leo. -- http://mail.python.org/mailman/listinfo/python-list
