tagged-methods.py

#!/usr/bin/env python3

class TaggedMethods(type):
    def __new__(cls, name, bases, body):
        tags = {}
        for name, attr in ((k,v) for k,v in body.items() if isinstance(v, Tag)):
            tags.setdefault(attr.tag, []).append(name)
            body[name] = attr.func
        body['methods_by_tag'] = property(lambda s: {k:[getattr(s,a) for a in v] for k,v in tags.items()})
        return type.__new__(cls, name, bases, body)

class Tag:
    def __init__(self, tag):
        self.tag = tag
    def __call__(self, func):
        self.func = func
        return self

# a class with methods that are tagged/typed as either calc methods or display methods
class Foo(metaclass = TaggedMethods):
    @Tag('calc')
    def ham(self):
        pass

    @Tag('calc')
    def spam(self):
        pass

    @Tag('disp')
    def eggs(self):
        pass

foo = Foo()
print(foo.methods_by_tag['calc'])
print(foo.methods_by_tag['disp'])