api.py

import functools


class Api:

    def __init__(self):
        self.apis = []

    def register(self, f):
        self.apis.append(f.__name__)
        
        @functools.wraps(f)
        def wrapper(*args, **kwargs):
            f(*args, **kwargs)
        
        return wrapper

foo.py

import api


myapi = api.Api()

@myapi.register
def p(s, q=None):
    print(s)
    print(q)

@myapi.register
def b():
    print('b')

myapi2 = api.Api()

@myapi2.register
def c():
    print('c')

print(myapi.apis)
print(myapi2.apis)
p('s', q='q')