Python True Value Testing

gistfile1.py

#!/usr/bin/env python
#vi: encoding=utf-8

__author__ = "dreampuf <soddyque@gmail.com>"

"""
Reference : http://docs.python.org/2/library/stdtypes.html#truth-value-testing
"""

class S(object):
    def __str__(self):
        return "<{0} o={{2}}>".format(self.__class__, self.o)

class A(S):
    def __init__(self, o):
        self.o = o
    def __len__(self):
        print "A, len"
        return self.o

class B(S):
    def __init__(self, o):
        self.o = o
    def __nonzero__(self):
        print "B, nonzero"
        return self.o

    def __len__(self):
        print "B, len"
        return self.o

a0, a1 = A(0), A(1)
bT, bF = B(True), B(False)

for i in (None, False, 0, 0L, 0.0, 0j, '', (), [], {}, a0, a1, bT, bF):
    if i:
        print True, i
    else:
        print False, i

""" 
#output:
False None
False False
False 0
False 0
False 0.0
False 0j
False 
False ()
False []
False {}
A, len
False <<class '__main__.A'> o={2}>
A, len
True <<class '__main__.A'> o={2}>
B, nonzero
True <<class '__main__.B'> o={2}>
B, nonzero
False <<class '__main__.B'> o={2}>
"""