以艰难的方式学习 Python，例 49:使用 assert_equal 比较对象 [英] Learn Python the Hard Way, Ex 49 : Comparing objects using assert_equal

问题描述

是否可以使用 assert_equal 来比较对象?我一直看到这个错误:

Is it possible to use assert_equal to compare objects? I keep seeing this error:

AssertionError: <ex49.parser.Sentence object at 0x01F1BAF0> !=
<ex49.parser.Sentence object at 0x01F1BB10>

相关代码片段:

def test_parse_subject():

    testsentence = "princess go east"
    result = lexicon.scan(testsentence)
    Sent = parse_sentence(result)
    ResultSent = Sentence(('subject', 'princess'),
                      ('verb', 'go'),
                      ('object', 'east'))
    print ResultSent.subject
    print ResultSent.verb
    print ResultSent.object
    print Sent.subject
    print Sent.verb
    print Sent.object
    assert_equal(Sent, ResultSent)

屏幕上的打印输出表明对象具有相同的内容 - 但出现断言错误.为什么是这样?有没有办法使用 assert_equal 来覆盖它?

The print outputs on screen suggests that the objects have the same contents - yet the assertion error shows up. Why is this? Is there some way to use assert_equal to override this?

推荐答案

我相信你需要在 Sentence 类上实现 __eq__ 方法.

I believe you need to implement the __eq__ method on the Sentence class.

assertEqual(first, second, msg=None)¶测试 first 和 second 是否相等.如果比较的值不相等，则测试将失败.

assertEqual(first, second, msg=None)¶ Test that first and second are equal. If the values do not compare equal, the test will fail.

此外，如果 first 和 second 是完全相同的类型，并且是 list、tuple、dict、set、frozenset 或 unicode 中的一个或子类向 addTypeEqualityFunc() 注册的任何类型，则将调用特定于类型的相等函数以生成更有用的默认错误消息(另请参阅特定于类型的方法列表).

In addition, if first and second are the exact same type and one of list, tuple, dict, set, frozenset or unicode or any type that a subclass registers with addTypeEqualityFunc() the type-specific equality function will be called in order to generate a more useful default error message (see also the list of type-specific methods).

Python 单元测试文档

操作符和方法名的对应关系如下:xlt(y)，x<=y调用x.le(y)，x==y调用x.eq(y), x!=y 和 x<>y 调用 x.ne(y), x>y 调用 x.gt(y),并且 x>=y 调用 x.ge(y).

The correspondence between operator symbols and method names is as follows: xlt(y), x<=y calls x.le(y), x==y calls x.eq(y), x!=y and x<>y call x.ne(y), x>y calls x.gt(y), and x>=y calls x.ge(y).

Python 数据模型文档

示例:

import unittest


class A:

    def __init__(self, num):
        self.num = num

    def __eq__(self, other):
        return self.num == other.num


class Test(unittest.TestCase):

    def test(self):
        a1 = A(1)
        a12 = A(1)
        a2 = A(2)

        self.assertEqual(a1, a1, 'a1 != a1')
        self.assertEqual(a1, a12, 'a1 != a12')
        self.assertEqual(a1, a2, 'a1 != a2')

def main():
    unittest.TestRunner(Test())

if __name__ == '__main__':
    unittest.main()

现在评论 __eq__ 方法并查看不同之处.

Now comment the __eq__ method and see the difference.

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