Python, from version 2.3 forward, has a
bool type which is a subclass of
int, the standard integer type.
It has two possible values:
False, which are special versions of 1 and 0 respectively and behave as such in arithmetic contexts.
Also, a numeric value of zero (integer or fractional), the null value (
None), the empty string, and empty containers (i.e. lists, sets, etc.) are considered Boolean false; all other values are considered Boolean true by default.
Classes can define how their instances are treated in a Boolean context through the special method
__nonzero__ (Python 2) or
__bool__ (Python 3). For containers,
__len__ (the special method for determining the length of containers) is used if the explicit Boolean conversion method is not defined.
This article uses content from Wikipedia:Boolean
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