class A(object):
    def test(self):
        return "Tset"

    def __call__(self):
        return "Eaxmple"

a = A()
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))
a.__call__ = lambda : "Example"
a.test = lambda : "Test"
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))

print(a())
print("Explicit call: {0}".format(a.__call__()))
print(a.test())

call method: <bound method A.__call__ of <__main__.A object at 0x7f3f2d60b6a0>>
test method: <bound method A.test of <__main__.A object at 0x7f3f2d60b6a0>>
call method: <function <lambda> at 0x7f3f2ef4ef28>
test method: <function <lambda> at 0x7f3f2d5f8f28>
Eaxmple
Explicit call: Example
Test

...
Example
Explicit call: Example
Test