如何在Pytest中猴子动态类属性

Question

I use Pytest and I want to test a class which has a dynamic attribute set by a function

Here is an example

file_1.py

def fn():
    return 'foo'

class Cls(object):
    cls_attr = fn()

test_file_1.py

import file_1

def test_cl1(monkeypatch):
    monkeypatch.setattr('file_1.fn', lambda: 'bar')
    assert file_1.fn() == 'bar'
    cls = file_1.Cls()
    assert cls.cls_attr == 'bar' # <-- fail here

I think that python "compile"s the class before, then monkeypatch is run after.

Is there a way to "reload" the class with the monkeypatched function?

Answer 1

I don't think so... but why not monkeypatch the Cls.cls_attr instead?

ETA: Perhaps what you want to use instead of monkeypatch is mock . There is a pytest-mock plugin that may be useful with it too.