[Python-Dev] [872326] generator expression implementation

Hello, Sorry to bring this out again, I didn't find a reference about the following issue in generator expressions: (for x in expr) When should 'expr' be evaluated? A priori, one would expect it to be evaluated immediately, but it is not what the suggested implementation does: def __gen(): for x in expr: yield x __gen() This only computes expr when the first element of the generator is needed (so it may even never be computed). Is it done purposefully? It may also be surprising to see the anonymous generator in tracebacks if an exception is raised within expr. A bientot, Armin.