The following values are considered false:
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None
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False
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zero of any numeric type, for example, 0, 0L, 0.0, 0j.
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any empty sequence, for example, '', (), [].
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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 or bool value False. [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.)
