anything.py

"""
Defines the `Anything` and `Something` constants.

`Anything` compares true with any other object:

>>> Anything == 42
True
>>> 'hello' == Anything
True

You can use it to check that specific values in a data structure
have a value, but it doesn't matter what they are,
for example in a unit test:

>>> [1, 2, 3] == [1, Anything, 3]
True
>>> {'x': 10, 'y': -3} == {'x': 10, 'y': Anything}
True
>>> {'x': 10} == {'x': 10, 'y': Anything}
False

Inequality behaves consistently with equality:

>>> 'hello' != Anything
False

Even None is considered equal to Anything:

>>> Anything == None
True

If you want to make sure that a value is not None, use `Something`
instead:

>>> Something == None
False
>>> Something == 1
True
>>> 1 == Something
True
>>> Something != None
True
>>> Something != 'foo'
False

`Something` only checks for None specifically, i.e. it does not accept any
falsy value:

>>> Something == False
True
>>> Something != False
False

Equality between the two constants works as you probably expect:

>>> Anything == Anything
True
>>> Something == Something
True
>>> Anything == Something
True
>>> Something == Anything
True
"""

__all__ = ['Anything', 'Something']


class AnythingType(object):
    def __eq__(self, other):
        return True

    def __ne__(self, other):
        return False

    def __repr__(self):
        return 'Anything'

Anything = AnythingType()


class SomethingType(object):
    def __eq__(self, other):
        return other is not None

    def __ne__(self, other):
        return other is None

    def __repr__(self):
        return 'Something'

Something = SomethingType()


if __name__ == '__main__':
    import doctest
    doctest.testmod()