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2.2.1 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- 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 zero.2.5
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 for false and 1 for true, unless otherwise
stated. (Important exception: the Boolean operations
"or" and "and" always return one of
their operands.)
Footnotes
- ... zero.2.5
- Additional information on these special methods may be found in the Python Reference Manual.
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Release 2.2, documentation updated on December 21, 2001.