__call__
examples: http://stackoverflow.com/a/5824909/433940
Memoization: http://stackoverflow.com/a/5824909/433940
Singleton pattern: http://stackoverflow.com/q/6760685/433940
Bound/Unbound Methods: http://stackoverflow.com/a/13348193/433940
Decorators: http://stackoverflow.com/a/1594484/433940
Generators: http://stackoverflow.com/a/231855/433940
Metaclasses: http://stackoverflow.com/a/6581949/433940
Current Module: http://stackoverflow.com/a/2933481/433940
Get current module for use in getattr()
or setattr()