Secret Recipes of the Python Ninja

Bijection

1. Bijective functions are commonly found in a variety of mathematical areas, such as in the definitions of isomorphism, homeomorphism, diffeomorphism, permutation group, and projective maps. The following example only demonstrates how a bijection object is created and checked, but doesn't go into extensive detail on implementation:

      >>> from collections_extended import bijection      >>> bij = bijection({'a': 1, 'b': 2, 'c': 3})      >>> bij.inverse[2]      'b'      >>> bij['a'] = 2      >>> bij == bijection({'a': 2, 'c': 3})      True      >>> bij.inverse[1] = 'a'      >>> bij == bijection({'a': 1, 'c': 3})      True

• • As usual, the class is imported from the module and an instance is created. The instance argument is a simple dictionary, mapping a string to an integer. ...