bool

https://docs.python.org/3/library/constants.html

https://docs.python.org/3/library/functions.html#bool

INTRODUCTION

Any object can be tested for truth value.

Objects considered false:

• constants defined to be false: 'None' and 'False',
• zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1),
• empty sequences and collections: '', tuple(), [], {}, set(), range(0),
• empty strings,
• objects with a '__bool__()' method that returns 'False' (Py3),
• objects with a '__nonzero__()' method that returns 'False' (Py2),
• objects with a '__len__()' method that returns zero.

Everything else is considered true.

'True' and 'False' are instances of the 'bool' class which is inherited from 'int'. In numeric contexts (for example when used as the argument to an arithmetic operator), 'False' and 'True' behave like the integers 0 and 1, respectively.

BOOLEAN OPERATIONS

'A or B', 'A and B', 'not A' (ascending priority).

'A or not B and C' is interpreted as 'A or ((not B) and C)'.

'not A == B' is interpreted as 'not (A == B)' ('==' is a non-Boolean operator!).

Use parentheses () in case of doubt.

'and' and 'or' are short-circuit operators:

• 'False and Anything' returns 'False', 'Anything' is not checked,
• 'True and Anything' returns 'Anything', but not converted to 'bool',
• 'True or Anything' returns 'True', 'Anything' is not checked,
• 'False or Anything' returns 'Anything', but not converted to 'bool'.

COMPARISONS

'A == B', 'A != B', 'A < B', 'A <= B', 'A > B', 'A >= B'.

Identity tests: 'A is B' [id(A) == id(B)], 'A is not B'.

'x in S' and 'x not in S' operations are supported by types that are iterable or implement the '__contains__()' method.