Monkey Patching is the dynamic replacement of attributes at runtime.

E.g.:

1from SomeOtherProduct.SomeModule import SomeClass
2
3def speak(self):
4  return "ook ook eee eee eee!"
5
6SomeClass.speak = speak

The code for the method speak of the class SomeClass has been replaces at runtime.

Consider a class that has a method get_data. This method does an external lookup, and various 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_data method with a stub that returns some fixed data.

Use caution when monkeypatching:

1. If anything else besides your test logic calls get_data as well, it will also call your monkey-patched replacement rather than the original.
2. If some variable or attributes exists that also points to the get_data function by the time it gets replaces, this alias will not change its meaning and will continue to point to the original get_data.

References

• https://stackoverflow.com/questions/5626193/what-is-monkey-patching