Python builtin “all” with generators

Question

I have the following problem with python\'s \"all\" and generators:

G = (a for a in [0,1])
all(list(G))   # returns False - as I expected

B

Answer 1

No, it doesn't. The following snippet returns False

G = (a for a in [0,1])
all(G)         # returns False

Are you perhaps doing the following

G = (a for a in [0,1])
all(list(G))   # returns False
all(G)         # returns True!

In that case, you are exhausting the generator G when you construct the list, so the final call to all(G) is over an empty generator and hence returns the equivalent of all([]) -> True.

A generator can't be used more than once.