[Python-ideas] Make len() usable on a generator

[Stephen J. Turnbull]

Thomas Chaumeny writes:

 > Yes, it has to exhaust the generator to find the length, but that also is
 > what list(generator) or sum(generator) have to do and yet they are allowed
 > constructions.

sum(1 for x in generator)

I'm on the fence about whether I prefer that to len(generator), on the
grounds that I normally would not expect len to use up the sequence,
while I sort of expect sum to do so (for values of "sort of expect"
that acknowledge that

    s = [1, 2, 3]
    print(sum(s))

doesn't "use up" s in fact, but it does "use" all the values).