override method

js

var Hoge = function (){};
Hoge.prototype.foo = function (){
  return 'hello';
};

var a = new Hoge();
a.foo();
# ==> 'hello'

var bar = function (){
  return 'world';
};

var foo = a.foo;
a.foo = bar;
a.foo();
# ==> 'world'

foo()
# ==> 'hello'

py

class Hoge:
  def foo(self):
    return 'hello'

a = Hoge()
a.foo()
# ==> 'hello'

def bar():
  return 'world'

foo = a.foo
a.foo = bar
a.foo()
# ==> 'world'

foo()
# ==> 'hello'