[Python-ideas] Fwd: Boolean behavior of None

[Ilkka Pelkonen]

Hi all,
I ran into an issue in expression evaluation with Python for Windows 2.7.3.
Consider the following code:

expected_result = (expected_string != 'TRUE') # Boolean
element = find_element() # Can return None or an instance of Element
flag = (element and element.is_visible())
if flag == expected_result:
..# Ok
..return
# Otherwise perform some failure related stuff.

This code does not work. What happens on the 'flag' assignment row, is that
if 'element' is None, the expression returns None, not False. This makes
the if comparison to fail if expected_result is False, since boolean False
is not None.

To me as a primarily C++ programmer it seems there could be two different
changes here, either change the behavior of the 'and' expression, forcing
it to return Boolean even if the latter part is not evaluated, and/or make
the comparison "False == None" return True. Although potentially complex,
I'd myself go for the first approach. It seems to me more logical that
False != None than an 'and' expression returning non-boolean. Also the
latter change might require people change their code, while the former
should not require any modifications.

This behavior probably results in lots of errors when people like me, used
to more traditional languages, take on Python in a serious manner. I like
the concept 'pythonic', and am trying to apply it to practice like above.

Hoping to hear your thoughts,
Regards,

Ilkka Pelkonen
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