Hm. What if list comprehensions returned a "lazy list", that if you took an iterator of it, you'd get a generator-iterator, but if you tried to use it as a list, it would populate itself? Then there'd be no need to ever *not* use a listcomp, and only one syntax would be necessary.
More specifically, if all you did with the list was iterate over it, and then throw it away, it would never actually populate itself. The principle drawback to this idea from a semantic viewpoint is that listcomps can be done over expressions that have side-effects. :(
I don't think this can be done without breaking b/w compatibility. Example: a = [x**2 for x in range(10)] for i in a: print i print a Your proposed semantics would throw away the values in the for loop, so what would it print in the third line? --Guido van Rossum (home page: http://www.python.org/~guido/)