gistfile1.txt

>>> ( x for x in [1,2,3] )
<generator object <genexpr> at 0x7f7de8dc6cd0>
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> # OK, seems legit
>>> { x:x for x in [1,2,3] }
{1: 1, 2: 2, 3: 3}
>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> # So far so good...
>>> [ x for x in [1,2,3] ]
[1, 2, 3]
>>> x
3
>>> # MIND = BLOWN