Is False 0 and True 1 an implementation detail or is it guaranteed by the language

Question

Is it guaranteed that False    0 and True    1  in Python  assuming that they are not reassigned by the user    For instance  is it in any way guaranteed that the following code will always produce the same results  whatever the version of Python  both existing and  likely  future ones    0    False    True 1    True     True   zero    one   False     is  zero    Any reference to the official documentation would be much appreciated   Edit  As noted in many answers  bool inherits from int   The question can therefore be recast as   Does the documentation officially say that programmers can rely on booleans inheriting from integers  with the values 0 and 1     This question is relevant for writing robust code that won t fail because of implementation details

User · Answer

Link to the PEP discussing the new bool type in Python 2.3: http://www.python.org/dev/peps/pep-0285/.

When converting a bool to an int, the integer value is always 0 or 1, but when converting an int to a bool, the boolean value is True for all integers except 0.

>>> int(False)
0
>>> int(True)
1
>>> bool(5)
True
>>> bool(-5)
True
>>> bool(0)
False

User · Answer

In Python 2 x this is not guaranteed as it is possible for True and False to be reassigned   However  even if this happens  boolean True and boolean False are still properly returned for comparisons  In Python 3 x True and False are keywords and will always be equal to 1 and 0  Under normal circumstances in Python 2  and always in Python 3  False object is of type bool which is a subclass of int  object       int       bool  It is the only reason why in your example    zero    one   False  does work  It would not work with an object which is not a subclass of integer  because list indexing only works with integers  or objects that define a   index   method  thanks mark-dickinson   Edit  It is true of the current python version  and of that of Python 3  The docs for python 2 and the docs for Python 3 both say   There are two types of integers        Integers  int        Booleans  bool   and in the boolean subsection   Booleans  These represent the truth values False and True       Boolean values behave like the values 0 and 1  respectively  in almost all contexts  the exception being that when converted to a string  the strings  quot False quot  or  quot True quot  are returned  respectively   There is also  for Python 2   In numeric contexts  for example when used as the argument to an arithmetic operator   they  False and True  behave like the integers 0 and 1  respectively   So booleans are explicitly considered as integers in Python 2 and 3  So you re safe until Python 4 comes along   -

User · Answer

In Python 2 x  it is not guaranteed at all    gt  gt  gt  False   5  gt  gt  gt  0    False False   So it could change  In Python 3 x  True  False  and None are reserved words  so the above code would not work   In general  with booleans you should assume that while False will always have an integer value of 0  so long as you don t change it  as above   True could have any other value  I wouldn t necessarily rely on any guarantee that True  1  but on Python 3 x  this will always be the case  no matter what

[python] Is False == 0 and True == 1 an implementation detail or is it guaranteed by the language?

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