As an expression(in the grammar):
-
[i for i in [1,2,3]]is a list comprehension; -
(i for i in [1,2,3])is a general expression; - But
i for i in [1,2,3]by itself is a syntax error, and that's just the way it is. There must be something surrounding it. Unless you have ( or [ around it, it's not a valid expression, because the for keyword is not valid at that point.
