Python模拟:包装实例方法
Python模拟:包装实例方法
提问于 2017-06-27 04:51:51
我想要的是：确保在with语句中创建的所有Foo实例都通过wraps=Foo.foo将其foo实例方法包装在MagicMock中。我希望这样做的原因是，我可以在方法foo上跟踪所创建的所有Foo实例的call_count。现在我这么说似乎是不可能的.
>>> from mock import patch
...
... class Foo(object):
...
... def foo(self):
... return "foo"
...
... with patch("__main__.Foo.foo", wraps=Foo.foo) as m:
... foo = Foo()
... print(foo.foo())
Traceback (most recent call last):
File "a.py", line 12, in <module>
print(foo.foo())
File "/disk/software/lib/python27/mock/mock.py", line 1062, in __call__
return _mock_self._mock_call(*args, **kwargs)
File "/disk/software/lib/python27/mock/mock.py", line 1132, in _mock_call
return self._mock_wraps(*args, **kwargs)
TypeError: unbound method foo() must be called with Foo instance as first argument (got nothing instead)问题模拟的foo方法没有绑定到通过foo = Foo()创建的foo实例，因为它包装了未绑定的方法Foo.foo。有人知道如何确保被模拟的方法绑定到实例吗？
我已经知道的：
>>> foo = Foo()
... with patch.object(foo, "foo", wraps=foo.foo) as m:
... print(foo.foo())
"foo"但这并不能满足我的约束，即对象必须在patch上下文中实例化。
回答 2
Stack Overflow用户
回答已采纳
发布于 2018-08-04 05:01:46
我上面提出的不正确的解决方案的问题
with patch("__main__.Foo.foo", wraps=Foo.foo) as m:
...Foo上的foo方法被模拟为包装未绑定的方法Foo.foo，这自然不起作用，因为未绑定的方法Foo.foo在以后调用时不知道它附加到了哪个实例。
我能想到的最简单的解决方案
from mock import patch, MagicMock
class Foo:
def foo(self):
return "foo"
class MockFoo(Foo):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
# Every instance of MockFoo will now have its `foo` method
# wrapped in a MagicMock
self.foo = MagicMock(wraps=self.foo)
with patch("__main__.Foo", MockFoo) as m:
foo = Foo()
print(foo.foo())
assert foo.foo.call_count == 1Stack Overflow用户
发布于 2021-04-28 18:27:55
这对于Python mock来说是如此令人讨厌，以至于我最终构建了一个自定义的补丁实现(如果需要的话，可以扩展其他特性)。
import contextlib
class Patcher:
UNCHANGED_RET = object()
def __init__(self):
self.call_count = 0
self.return_value = Patcher.UNCHANGED_RET
@contextlib.contextmanager
def patch(klass, method_name):
patcher = Patcher()
orig_method = getattr(klass, method_name)
def new_method(myself, *args, **kwargs):
patcher.call_count += 1
orig_return_value = orig_method(myself, *args, **kwargs)
if patcher.return_value != Patcher.UNCHANGED_RET:
return patcher.return_value
return orig_return_value
setattr(klass, method_name, new_method)
yield patcher
setattr(klass, method_name, orig_method)使用方法如下：
class MyClass:
def f(self):
return 42
x = MyClass()
with patch(MyClass, 'f') as f_patcher:
y = MyClass() # inside or outside -- does not matter
assert x.f() == 42
assert f_patcher.call_count == 1
f_patcher.return_value = 7
assert y.f() == 7
assert f_patcher.call_count == 2页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/44768483
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