Python 'del' 如果在 Python 3.6 上模拟调用时引发 AttributeError，但在 >=3.7 上不会

Question

我正在使用 unittest.mock 来测试我的代码。如果对象不存在，我创建的函数会使用 hasattr.

向该对象添加一个属性

根据 Python 3.6 and newer versions 中的文档，我可以使用 del 删除 mock 的属性，但它在 Python 3.6 上失败了。在 Python 3.7 及更高版本上，它有效。

这是一个简短的测试，展示了我要测试的内容：

from unittest.mock import Mock

def add_attribute(info):
    if not hasattr(info, 'attribute'):
        info.attribute = 'Attribute Added'

def test_mock():
    info = Mock()
    assert hasattr(info, 'attribute')
    del info.attribute
    assert not hasattr(info, 'attribute')
    add_attribute(info)
    assert info.attribute == 'Attribute Added'
    del info.attribute
    assert not hasattr(info, 'attribute')

在 python 3.8 上有效：

======= test session starts ========
platform linux -- Python 3.8.5, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /code
plugins: cov-2.12.1
collected 1 item                                                                                                                                                                                                         

test.py .

在 python 3.6 上，它失败了：

============================= test session starts ==============================
platform linux -- Python 3.6.14, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /code
plugins: cov-2.12.1
collected 1 item                                                               

test.py F                                          [100%]

=================================== FAILURES ===================================
__________________________________ test_mock ___________________________________

    def test_mock():
        info = Mock()
        assert hasattr(info, 'attribute')
        del info.attribute
        assert not hasattr(info, 'attribute')
        add_attribute(info)
        assert info.attribute == 'Attribute Added'
>       del info.attribute

test.py:14: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <Mock id='140171347130128'>, name = 'attribute'

    def __delattr__(self, name):
        if name in _all_magics and name in type(self).__dict__:
            delattr(type(self), name)
            if name not in self.__dict__:
                # for magic methods that are still MagicProxy objects and
                # not set on the instance itself
                return
    
        if name in self.__dict__:
            object.__delattr__(self, name)
    
        obj = self._mock_children.get(name, _missing)
        if obj is _deleted:
>           raise AttributeError(name)
E           AttributeError: attribute

/usr/local/lib/python3.6/unittest/mock.py:728: AttributeError
=========================== short test summary info ============================
FAILED test.py::test_mock - AttributeError: attribute
============================== 1 failed in 0.11s ===============================
test_python exited with code 1

我不确定 unittest 库是否已更新，或者它可能是关于如何在 Python 版本之间传递函数的（非）预期行为。

如有任何见解，我们将不胜感激。

Answer 1

这已在 222d303 for issue bpo-20239

中修复

这已在 d358a8c which first appeared in python 3.7.3rc1

中移植到 3.7

此补丁对 mocks

上的 __delattr__ 方法进行了重大更改

~<3.7.3代码摘录：

    def __delattr__(self, name):
        # ...

        if name in self.__dict__:
            object.__delattr__(self, name)

        obj = self._mock_children.get(name, _missing)
        if obj is _deleted:
            raise AttributeError(name)

并将其与 3.7.3+ 代码进行比较：

    def __delattr__(self, name):
        # ...

        obj = self._mock_children.get(name, _missing)
        if name in self.__dict__:
            _safe_super(NonCallableMock, self).__delattr__(name)
        elif obj is _deleted:
            raise AttributeError(name)

在重复删除的情况下，3.6 代码会触发 AttributeError（由于第一个删除设置 _deleted）——但修复了它以避免这种情况（通过elif)

Python 'del' 如果在 Python 3.6 上模拟调用时引发 AttributeError，但在 >=3.7 上不会

Python 'del' raises AttributeError if called on mock on Python 3.6, but not on >=3.7

python

mocking

pytest