What is monkey patching in Python?

In Python, the term monkey patch only refers to dynamic modifications of a class or module at run-time.

Consider the below example:

# m.py
class MyClass:
def f(self):
print “f()”
We can then run the monkey-patch testing like this:

import m
def monkey_f(self):
print “monkey_f()”

m.MyClass.f = monkey_f
obj = m.MyClass()
obj.f()
The output will be as below:

monkey_f()
As we can see, we did make some changes in the behavior of f() in MyClass using the function we defined, monkey_f(), outside of the module m.