isinstance 和 Mocking

问题描述

类 HelloWorld(object):def say_it(self):返回'你好我是你好世界'def i_call_hello_world(hw_obj):print 'here... 检查类型:%s' %type(HelloWorld)如果是实例(hw_obj，HelloWorld):打印 hw_obj.say_it()来自模拟导入补丁，MagicMock导入单元测试类TestInstance(unittest.TestCase):@patch('__main__.HelloWorld', spec=HelloWorld)def test_mock(self,MK):印刷类型(MK)MK.say_it.return_value = '我是假的'v = i_call_hello_world(MK)打印 v如果 __name__ == '__main__':c = 你好世界()i_call_hello_world(c)打印 isinstance(c, HelloWorld)单元测试.main()

这是回溯

这里...检查类型:<type 'type'>你好我是你好世界真的<类'mock.MagicMock'>这里...检查类型:<class 'mock.MagicMock'>乙=========================================================================错误:test_mock (__main__.TestInstance)----------------------------------------------------------------------回溯(最近一次通话最后):文件/usr/local/lib/python2.7/dist-packages/mock.py"，第 1224 行，已修补返回函数(*args，**keywargs)文件t.py"，第 18 行，在 test_mockv = i_call_hello_world(MK)i_call_hello_world 中的文件t.py"，第 7 行如果是实例(hw_obj，HelloWorld):TypeError: isinstance() arg 2 必须是类、类型或类和类型的元组----------------------------------------------------------------------在 0.002 秒内运行 1 次测试

Q1.为什么会抛出这个错误?它们是 <class type='MagicMock>

Q2.如果错误得到修复，如何暂停模拟以便第一行通过?

来自 文档:p><块引用>

通常，对象的 __class__ 属性将返回其类型.对于具有规范的模拟对象，__class__ 改为返回规范类.这允许模拟对象通过 isinstance() 测试它们正在替换/伪装为的对象:

mock = Mock(spec=3)isinstance(模拟，int)真的

解决方案

不要使用 isinstance，而是检查 say_it 方法是否存在.如果方法存在，调用它:

if hasattr(hw_obj, 'say_it'):打印 hw_obj.say_it()

无论如何，这是一个更好的设计:依赖类型信息更加脆弱.

class HelloWorld(object):
    def say_it(self):
        return 'Hello I am Hello World'

def i_call_hello_world(hw_obj):
    print 'here... check type: %s' %type(HelloWorld)
    if isinstance(hw_obj, HelloWorld):
        print hw_obj.say_it()

from mock import patch, MagicMock
import unittest

class TestInstance(unittest.TestCase):
    @patch('__main__.HelloWorld', spec=HelloWorld)
    def test_mock(self,MK):
        print type(MK)
        MK.say_it.return_value = 'I am fake'
        v = i_call_hello_world(MK)
        print v

if __name__ == '__main__':
    c = HelloWorld()
    i_call_hello_world(c)
    print isinstance(c, HelloWorld)
    unittest.main()

Here is the traceback

here... check type: <type 'type'>
Hello I am Hello World
True
<class 'mock.MagicMock'>
here... check type: <class 'mock.MagicMock'>
E
======================================================================
ERROR: test_mock (__main__.TestInstance)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/mock.py", line 1224, in patched
    return func(*args, **keywargs)
  File "t.py", line 18, in test_mock
    v = i_call_hello_world(MK)
  File "t.py", line 7, in i_call_hello_world
    if isinstance(hw_obj, HelloWorld):
TypeError: isinstance() arg 2 must be a class, type, or tuple of classes and types

----------------------------------------------------------------------
Ran 1 test in 0.002s

Q1. Why is this error thrown? They are <class type='MagicMock>

Q2. How do I pause the mocking so that the first line will pass if the error is fixed?

From the docs:

Normally the __class__ attribute of an object will return its type. For a mock object with a spec, __class__ returns the spec class instead. This allows mock objects to pass isinstance() tests for the object they are replacing / masquerading as:

mock = Mock(spec=3)
isinstance(mock, int)
True

解决方案

Don't use isinstance, instead check for the existence of the say_it method. If the method exists, call it:

if hasattr(hw_obj, 'say_it'):
    print hw_obj.say_it()

This is a better design anyway: relying on type information is much more brittle.