Rationale

Allows working with objects depending on their current behaviour, not their type or their registered (ABC-like) interface.

Quick example:

from ducktypes.ducktype import Duck

class MyObject(object):
    def some_method(self, a, b):
        pass
    def another_method(self, x):
        pass


class AnotherObject(object):
    def some_method(self, a, b):
        pass
    def another_method(self, a):
        pass

class AnotherDifferentObject(object):
    def some_method(self, a, b, c):
        pass
    def another_method(self, a):
        pass

duck = Duck(MyObject())

print "AnotherObject instances implement MyObject interface: ", duck.maybe_implemented_by(AnotherObject())
print "AnotherDifferentObject instances implement MyObject interface:", duck.maybe_implemented_by(AnotherDifferentObject())

Output:

AnotherObject instances implement MyObject interface:  True
AnotherDifferentObject instances implement MyObject interface: False

Gotchas

• positional arguments are supposed to be called as positional arguments, and keyword arguments are supposed to be called as positional arguments. If your client code calls keyword arguments as positional ones, signature matching may fail.

• proxy-everything methods, i.e. (*args, **kwargs)-like signature, will of course deceive our signature detection system.

Todo

• __getattr__ / __getattribute__ overriding functions

• subclasses exposing special methods with different signature

• C-declared functions that don’t expose their signature.

• implement optional strict checking.