Python Truth Value Testing Explained - A Python Programming Tutorial

Guide
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Any object can be tested for truth value, for use in an if or while condition or as operand of a Boolean operation like and , or , or not .

The following values are considered false:

  • None
  • False
  • zero of any numeric type, for example, 0 , 0.0 , 0j , Decimal(0) , Fraction(0, 1) .
  • any empty sequence, for example, '' , () , [] , set() , range(0) .
  • any empty mapping, for example, {} .
  • instances of user-defined classes, if the class defines a __bool__() or __len__() method, when that method returns False or 0 .

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.)

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