So the way I envision it is that *in the absence of a nonlocal or global declaration in the containing scope*, := inside a comprehension or genexpr causes the compiler to assign to a local in the containing scope, which is elevated to a cell (if it isn't already). If there is an explicit nonlocal or global declaration in the containing scope, that is honored. Examples: # Simplest case, neither nonlocal nor global declaration def foo(): [p := q for q in range(10)] # Creates foo-local variable p print(p) # Prints 9 # There's a nonlocal declaration def bar(): p = 42 # Needed to determine its scope def inner(): nonlocal p [p := q for q in range(10)] # Assigns to p in bar's scope inner() print(p) # Prints 9 # There's a global declaration def baz(): global p [p := q for q in range(10)] baz() print(p) # Prints 9 All these would work the same way if you wrote list(p := q for q in range(10)) instead of the comprehension. We should probably define what happens when you write [p := p for p in range(10)]. I propose that this overwrites the loop control variable rather than creating a second p in the containing scope -- either way it's probably a typo anyway. := outside a comprehension/genexpr is treated just like any other assignment (other than in-place assignment), i.e. it creates a local unless a nonlocal or global declaration exists. -- --Guido van Rossum (python.org/~guido)