How to replace a class method with mocked method for unit testing?

mock-method.py

#http://stackoverflow.com/questions/13073281/how-to-mock-pythons-datetime-now-in-a-class-method-for-unit-testing?rq=1
from mock import patch
from mock import Mock
import unittest

class MyCalc(object):

	def add(self,x ,y):
		return x+y
		
	def mul(self,x ,y):
		return x*y
	
	def return_something(self):
		return "something"



def mocked_return():
	return "mocked"

		
		
class MyCalcTest(unittest.TestCase):
	def setUp(self):
		self.calc = MyCalc()

	def test_mul_4_5(self):
		self.assertEqual( self.calc.mul(4,5), 20)

	def test_add_3_4(self):
		self.assertEqual( self.calc.add(3,4), 7)

	def test_mul_3_4(self):
		self.assertEqual( self.calc.mul(3,4), 12)

	def test_return_something(self):
		self.assertEqual( self.calc.return_something(), "something")

	@patch('__main__.MyCalc.return_something', Mock(side_effect=mocked_return))
	def test_mocked_return(self):
		self.assertEqual( self.calc.return_something(), "mocked")

		
if __name__ == '__main__':
    unittest.main()