How to overload Python's __bool__ method?

Question

Possible Duplicate:
defining “boolness” of a class in python

I thought this should print "False", why is it printing "True"?

>>> class Foo(object):
...   def __bool__(self):
...     return False
... 
>>> f = Foo()
>>> if f:
...   print "True"
... else:
...   print "False"
... 
True
>>>

Solution

You should define __nonzero__() in Python 2.x. It was only renamed to __bool__() in Python 3.x. (The name __nonzero__() actually predates the introduction of the bool type by many years.)

Comments

[Mehmet Kaan ERKOÇ]

It is strange that I could not find that information anywhere else but in your answer. Thanks a lot !

[Sven Marnach]

@MehmetKaanERKOÇ The documentation for most of the magic methods is on the data model page of the Python reference. Differences between Python 2 and 3 are mostly documented in the What's New page of Python 3.0. I'll admit this is not easy to find if you don't know what you are looking for.