1. Truth Value Testing¶
Any object can be tested for truth value, for use in an if
or
while
condition or as operand of the Boolean operations below. The
following values are considered false:
None
False
zero of any numeric type, for example,
0
,0L
,0.0
,0j
.any empty sequence, for example,
''
,()
,[]
.any empty mapping, for example,
{}
.instances of user-defined classes, if the class defines a
__nonzero__()
or__len__()
method, when that method returns the integer zero orbool
valueFalse
. [1]_
All other values are considered true — so objects of many types are always true.
Operations and built-in functions that have a Boolean result always return 0
or False
for false and 1
or True
for true, unless otherwise stated.
(Important exception: the Boolean operations or
and and
always return
one of their operands.)