False and 0 in the same dictionary

[Ben Finney]

Prateek <surekap at gmail.com> writes:

> >>> b = {0:'xyz', False:'abc'}
> >>> b
> {0: 'abc'}  # Am I the only one who thinks this is weird?

You're not the only one; I consider this a wart in Python.

False and True should be discrete values that don't compare equal with
any other value, not even ones that evaluate to boolean False or True.

    >>> False == []
    False
    >>> False == {}
    False
    >>> False == ''
    False
    >>> False == 0
    True

This is an artifact of the fact that ‘bool’ is a subclass of ‘int’,
and that ‘False’ is implemented such that it has the same hash as ‘0’:

    >>> isinstance(False, int)
    True
    >>> hash(False) == hash(0)
    True

The above is a legacy of the original lack of a boolean type in
Python, but it's confusing and IMO unnecessary these days. It should
be enough that they all evaluate to False in a boolean context:

    >>> bool([])
    False
    >>> bool({})
    False
    >>> bool('')
    False
    >>> bool(0)
    False

PEP 285 <URL:http://www.python.org/dev/peps/pep-0285>, that introduced
the ‘bool’ type, addresses this issue:

       In an ideal world, bool might be better implemented as a
       separate integer type that knows how to perform mixed-mode
       arithmetic.  However, inheriting bool from int eases the
       implementation enormously (in part since all C code that calls
       PyInt_Check() will continue to work -- this returns true for
       subclasses of int).  Also, I believe this is right in terms of
       substitutability: code that requires an int can be fed a bool
       and it will behave the same as 0 or 1.  Code that requires a
       bool may not work when it is given an int; for example, 3 & 4
       is 0, but both 3 and 4 are true when considered as truth
       values.

I wonder if any of that is relevant any more.

What does backward-compatibility-is-less-important Python 3 do (I
don't have it installed)? Is there a later PEP that I've missed which
finally makes ‘bool’ a type independent from ‘int’?

-- 
 \       “A ‘No’ uttered from deepest conviction is better and greater |
  `\       than a ‘Yes’ merely uttered to please, or what is worse, to |
_o__)                                  avoid trouble.” —Mahatma Gandhi |
Ben Finney