Python에서 인스턴스 메서드를 어떻게 추가하고 액세스합니까?

def foo():
    print("foo")

class A:
    def bar(self):
        print("bar")

a = A()

print(foo)  # <function foo at 0x00A98D70>
print(a.bar)  # <bound method A.bar of <__main__.A instance at 0x00A9BC88>>

def fooFighters(self):
    print("fooFighters")

A.fooFighters = fooFighters

a2 = A()
a2.fooFighters()  # fooFighters

# Also affects previously defined instances
a.fooFighters()  # fooFighters

def barFighters(self):
    print("barFighters")

a.barFighters = barFighters

a.barFighters()  # TypeError: barFighters() takes exactly 1 argument (0 given)

import types
a.barFighters = types.MethodType(barFighters, a)

a.barFighters()  # barFighters

# Other instances unaffected
a2.barFighters()  # AttributeError: A instance has no attribute 'barFighters'