Monkey patching in python

I was just reading an article about Martijn Pieters, who is a python expert, and he mentioned
monkey patching

I did not know what monkey patching is, so I googled it, and found a great answer on stack overflow

Basically, it takes advantage of python’s class access philosophy. Unlike java, which has a strict access policy, in python, all attributes and methods of a class are mutable. So it is possible to write code like this:

from SomeOtherProduct.SomeModule import SomeClass  
def speak(self):  
   return "ook ook eee eee eee!"  
SomeClass.speak = speak

This could be particularly useful for unittesting, which is also mentioned in the stackoverflow answer

For instance, consider a class that has a method get_data. This method does an external lookup (on a database or web API, for example), and various other methods in the class call it. However, in a unit test, you don’t want to depend on the external data source – so you dynamically replace the get_datamethod with a stub that returns some fixed data.

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