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Questions tagged [monkeypatching]

Dynamically modifying run-time behavior by replacing program elements with new program elements

Monkeypatching, in late-bound languages, refers to modifying run-time behavior by replacing program elements with new program elements.

Examples include replacing a method on a class with a new function, or patching a member of a class.

The term may have a pejorative connotation, as the technique is usually used on third-party code.

For more discussion, see "Monkeypatching for Humans" on Coding Horror.

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Adding a method to an existing object instance in Python

How do I add a method to an existing object (i.e., not in the class definition) in Python? I understand that it's not generally considered good practice to do so, except in some cases.
akdom
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What is monkey patching?

I am trying to understand, what is monkey patching or a monkey patch? Is that something like methods/operators overloading or delegating? Does it have anything common with these things?
Sergei Basharov
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When monkey patching an instance method, can you call the overridden method from the new implementation?

Say I am monkey patching a method in a class, how could I call the overridden method from the overriding method? I.e. Something a bit like super E.g. class Foo def bar() "Hello" end end class Foo def bar() super() + " World" …
James Hollingworth
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How to add property to a class dynamically?

The goal is to create a mock class which behaves like a db resultset. So for example, if a database query returns, using a dict expression, {'ab':100, 'cd':200}, then I would like to see: >>> dummy.ab 100 At first I thought maybe I could do it…
Anthony Kong
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Can I patch a Python decorator before it wraps a function?

I have a function with a decorator that I'm trying test with the help of the Python Mock library. I'd like to use mock.patch to replace the real decorator with a mock 'bypass' decorator which just calls the function. What I can't figure out is how…
Chris Sears
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Monkey patching a class in another module in Python

I'm working with a module written by someone else. I'd like to monkey patch the __init__ method of a class defined in the module. The examples I have found showing how to do this have all assumed I'd be calling the class myself (e.g. Monkey-patch…
Snorfalorpagus
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Can I add custom methods/attributes to built-in Python types?

For example—say I want to add a helloWorld() method to Python's dict type. Can I do this? JavaScript has a prototype object that behaves this way. Maybe it's bad design and I should subclass the dict object, but then it only works on the subclasses…
jedmao
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How does one monkey patch a function in python?

I'm having trouble replacing a function from a different module with another function and it's driving me crazy. Let's say I have a module bar.py that looks like this: from a_package.baz import do_something_expensive def a_function(): print…
guidoism
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What does 'Monkey Patching' exactly Mean in Ruby?

According to Wikipedia, a monkey patch is: a way to extend or modify the runtime code of dynamic languages [...] without altering the original source code. The following statement from the same entry confused me: In Ruby, the term monkey…
Yaser Sulaiman
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Can you patch *just* a nested function with closure, or must the whole outer function be repeated?

A 3rd party library we use contains a rather long function that uses a nested function inside it. Our use of that library triggers a bug in that function, and we very much would like to solve that bug. Unfortunately, the library maintainers are…
Martijn Pieters
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Making object JSON serializable with regular encoder

The regular way of JSON-serializing custom non-serializable objects is to subclass json.JSONEncoder and then pass a custom encoder to json.dumps(). It usually looks like this: class CustomEncoder(json.JSONEncoder): def default(self, obj): …
leonsas
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Monkey patching a @property

Is it at all possible to monkey patch the value of a @property of an instance of a class that I do not control? class Foo: @property def bar(self): return here().be['dragons'] f = Foo() print(f.bar) # baz f.bar = 42 #…
deceze
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Monkey-patch Python class

I've got a class, located in a separate module, which I can't change. from module import MyClass class ReplaceClass(object) ... MyClass = ReplaceClass This doesn't change MyClass anywhere else but this file. However if I'll add a method like…
ZooKeeper
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Can you monkey patch methods on core types in Python?

Ruby can add methods to the Number class and other core types to get effects like this: 1.should_equal(1) But it seems like Python cannot do this. Is this true? And if so, why? Does it have something to do with the fact that type can't be…
airportyh
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What is the difference between mocking and monkey patching?

I work with python and I'm a bit new to testing. I often see tests replacing an external dependency with a local method like so: import some_module def get_file_data(): return "here is the pretend file data" some_module.get_file_data =…
Jad S
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