Monkeypatching can be done without any library, but it has a number of repetitive (and kind of ugly) things it needs to do, so if you start to implement it yourself, you end up creating helpers to help with this. And naturally there a couple ready-to-use libraries to do it for you.
One way of monkeypatch is using Set class defined in stubout module of pymox package.
https://code.google.com/p/pymox/source/browse/trunk/stubout.py#108
monkeyPatch(module, 'myFunc', lambda n: someObject)
monkeypatch is only recommendable while unit testing the code if no other approach works to avoid it.
using monkeypatch in runtime to change the behaviour of class without affecting the class defination can be hazardous.
One way of monkeypatch is using Set class defined in stubout module of pymox package.
https://code.google.com/p/pymox/source/browse/trunk/stubout.py#108
monkeyPatch(module, 'myFunc', lambda n: someObject)
monkeypatch is only recommendable while unit testing the code if no other approach works to avoid it.
using monkeypatch in runtime to change the behaviour of class without affecting the class defination can be hazardous.
On the other hand mox.StubOutWithMock gives the ability to audit the behaviour of system under test making use of actual library returning the result by mocking whatever piece of code doesn't need to be used when under certain known condition return value of collaborative function is known.
