模拟：跟踪所有调用，Shell与程序不一致

Question

为什么在命令行中运行和在程序中运行时，mock.mock_calls的内容会不一样呢？当我在程序中检查mock.mock_calls == expected时，它会失败，但在命令行中却能通过。这段代码是根据文档中的示例来追踪多个调用的。(26.5.1.5. 追踪所有调用)

>>> from unittest.mock import MagicMock, call
>>> mock = MagicMock()
>>> mock.method()
<MagicMock name='mock.method()' id='57725952'>
>>> mock.attribute.method(10, x=53)
<MagicMock name='mock.attribute.method()' id='57775944'>
>>> mock.mock_calls
[call.method(), call.attribute.method(10, x=53)]
>>> mock.method_calls
[call.method(), call.attribute.method(10, x=53)]
>>> expected = [call.method(), call.attribute.method(10, x=53)]
>>> expected == mock.mock_calls
True
>>> expected == mock.method_calls
True

到目前为止，这一切都和预期的一样。但看看在程序中mock.mock_calls发生了什么：它记录了每个被调用方法的__str__方法的额外调用。而mock.method_calls没有受到影响。

import unittest.mock
mock = unittest.mock.MagicMock()
print(mock.method())
print(mock.attribute.method(10, x=53))
print('\nmock.mock_calls\n', mock.mock_calls)
print('\nmock.method_calls\n', mock.method_calls)

expected = [unittest.mock.call.method(),
            unittest.mock.call.attribute.method(10, x=53)]
print(expected == mock.mock_calls)
print(expected == mock.method_calls)

输出：

<MagicMock name='mock.method()' id='45740272'>
<MagicMock name='mock.attribute.method()' id='45850128'>

mock.mock_calls
 [call.method(),
 call.method().__str__(),
 call.attribute.method(10, x=53),
 call.attribute.method().__str__()]

mock.method_calls
 [call.method(), call.attribute.method(10, x=53)]
False
True

我在Windows 7的电脑上运行Python 3.4。

Answer 1

这是因为你在打印方法调用。这会导致调用一个叫做 __str__() 的特殊方法：

print(mock.method())
print(mock.attribute.method(10, x=53))

去掉 print() 的调用，你就会看到想要的效果：

mock.method()
mock.attribute.method(10, x=53)

顺便说一下，这是控制台中的一个例子：

>>> mock = unittest.mock.MagicMock()
>>> print(mock.method())
<MagicMock name='mock.method()' id='4433183576'>
>>> print(mock.attribute.method(10, x=53))
<MagicMock name='mock.attribute.method()' id='4433223752'>
>>> mock.mock_calls
[call.method(),
 call.method().__str__(),
 call.attribute.method(10, x=53),
 call.attribute.method().__str__()]

---

或者，你也可以使用一个普通的 Mock 类：

>>> mock = unittest.mock.Mock()
>>> print(mock.method())
<Mock name='mock.method()' id='4433235528'>
>>> print(mock.attribute.method(10, x=53))
<Mock name='mock.attribute.method()' id='4433252648'>
>>> mock.method_calls
[call.method(), call.attribute.method(10, x=53)]
>>> mock.mock_calls
[call.method(), call.attribute.method(10, x=53)]