[sago]

Yes, that was a pain. Particularly because it was only true of list comprehensions, not dict comprehensions or generators:

    Python 2.7.10 ...
    >>> a = 3
    >>> [a for a in range(10)]
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    >>> a
    9
    >>> a = 3
    >>> list(a for a in range(10))
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    >>> a
    3

Guido called it Python's 'dirty little secret'. It is fixed in Py3 though.