Rida Ayed · Feb 8, 2026

Patch private methods in python

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I’ve encountered this rather profane yet tricky problem while testing a method: class MyClass : def __method (self) -> str: pass def test () with patch . object(MyClass, "__method" ) as _: pass pytest E AttributeError: <class 'MyClass'> does not have the attribute '__method' A llm pointed to the name mangling cause. Changing __method to _MyClass__method fixes the error: def test () with…

I’ve encountered this rather profane yet tricky problem while testing a method:

class MyClass:

    def __method(self) -> str:
        pass

def test()
   with patch.object(MyClass,"__method") as _:
       pass

pytest

E           AttributeError: <class 'MyClass'> does not have the attribute '__method'

A llm pointed to the name mangling cause.
Changing ~~__method~~ to _MyClass__method fixes the error:

def test()
   with patch.object(MyClass,"_MyClass__method") as _:
       pass

The reason for this post, is that searching (ctrl+f) for ‘mangl’ or ‘priv’ yields nothing from the doc¹

https://docs.python.org/3/library/unittest.mock.html
↩︎

Read on /posts/patch-private-methods-in-python/ ↗

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