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Thu Mar 25 00:30:44 EST 2004 · https://mail.python.org/pipermail/python-dev/2004-March/043493.html

BTW, have we had an example of a generator expression where late binding was
semantically necessary?  The only one I recall was a strained one along the
lines of:

    sqs = (sq(i) for i in range(n))

    def sq(i):
        return i**2

Late binding was needed then because the generator expression referenced a
name not yet bound when the g-e was evaluated.

Is the popular plan now that this "will work", but provided that "n" is
bound before the g-e is evaluated?  That is, this works:

    n = 10
    sqs = (sq(i) for i in range(n))
    def sq(i): ...
    print list(sqs)

but this doesn't work:

    sqs = (sq(i) for i in range(n))
    n = 10  # swapped with the line above
    def sq(i): ...
    print list(sqs)

and this uses different bindings for the two lexical instances of "n" in the
g-e:

    n = 10
    sqs = (sq(i+n) for i in range(n)  # 10 used in range(n), 20 in i+n
    n = 20
    def sq(i): ...
    print list(sqs)

?

Not wondering how bad it can get, just wondering how bad it starts <wink>.

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Showing content from https://mail.python.org/pipermail/python-dev/2004-March/043493.html below:

[Python-Dev] Possible resolution of generator expression variablecapture dilemma