Nick Coghlan <ncogh...@gmail.com> added the comment:
Sure, you can technically do that, but you'll have to rewrite most of the
symtable pass in the compiler, since you won't be able to re-use the current
recursive descent algorithms (which are designed to handle function scopes).
That ran afoul of "If the implementation is hard to explain, it's a bad idea."
Where that gets particularly nasty is when you nest comprehensions with the
*same* iteration variable name:
>>> [[i for i in range(2)] for i in range(2)]
[[0, 1], [0, 1]]
Now your name generator needs to be clever enough to account for how many
levels deep it is. You also run into the lexical scoping problem anyway once a
lambda expression shows up:
>>> [[(lambda i=i: i)() for i in range(2)] for i in range(2)]
[[0, 1], [0, 1]]
>>> [[(lambda: i)() for i in range(2)] for i in range(2)]
[[0, 1], [0, 1]]
As noted earlier, not impossible to resolve, but for from the "simple" option
that folks seem to believe it is (and which I thought it would be before I
actually tried to implement it while respecting Python's lexical scoping rules).
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<https://bugs.python.org/issue10544>
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