我有一个类MyClass，它包含两个成员变量foo和bar:
class MyClass:
def __init__(self, foo, bar):
self.foo = foo
self.bar = bar
我有这个类的两个实例，每个实例都有相同的foo和bar值:
x = MyClass('foo', 'bar')
y = MyClass('foo', 'bar')
然而，当我比较它们是否相等时，Python返回False:
>>> x == y
False
我如何使python认为这两个对象相等?
当前回答
重写对象中的富比较运算符。
class MyClass:
def __lt__(self, other):
# return comparison
def __le__(self, other):
# return comparison
def __eq__(self, other):
# return comparison
def __ne__(self, other):
# return comparison
def __gt__(self, other):
# return comparison
def __ge__(self, other):
# return comparison
是这样的:
def __eq__(self, other):
return self._id == other._id
其他回答
如果你想逐个属性进行比较，并查看它是否以及在哪里失败，你可以使用下面的列表推导式:
[i for i,j in
zip([getattr(obj_1, attr) for attr in dir(obj_1)],
[getattr(obj_2, attr) for attr in dir(obj_2)])
if not i==j]
这里的额外优势是，当在PyCharm中调试时，您可以压缩一行并在“Evaluate Expression”窗口中输入。
总结如下:
It's advised to implement __eq__ rather than __cmp__, except if you run python <= 2.0 (__eq__ has been added in 2.1) Don't forget to also implement __ne__ (should be something like return not self.__eq__(other) or return not self == other except very special case) Don`t forget that the operator must be implemented in each custom class you want to compare (see example below). If you want to compare with object that can be None, you must implement it. The interpreter cannot guess it ... (see example below) class B(object): def __init__(self): self.name = "toto" def __eq__(self, other): if other is None: return False return self.name == other.name class A(object): def __init__(self): self.toto = "titi" self.b_inst = B() def __eq__(self, other): if other is None: return False return (self.toto, self.b_inst) == (other.toto, other.b_inst)
class Node:
def __init__(self, value):
self.value = value
self.next = None
def __repr__(self):
return str(self.value)
def __eq__(self,other):
return self.value == other.value
node1 = Node(1)
node2 = Node(1)
print(f'node1 id:{id(node1)}')
print(f'node2 id:{id(node2)}')
print(node1 == node2)
>>> node1 id:4396696848
>>> node2 id:4396698000
>>> True
当比较对象的实例时，将调用__cmp__函数。
如果==操作符在默认情况下不适用，您总是可以为对象重新定义__cmp__函数。
编辑:
如上所述，__cmp__函数自3.0起已弃用。 相反，你应该使用“丰富比较”方法。
在Python 3.7(及以上版本)中的数据类中，对象实例的相等性比较是一个内置特性。
Python 3.6提供了数据类的后端端口。
(Py37) nsc@nsc-vbox:~$ python
Python 3.7.5 (default, Nov 7 2019, 10:50:52)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from dataclasses import dataclass
>>> @dataclass
... class MyClass():
... foo: str
... bar: str
...
>>> x = MyClass(foo="foo", bar="bar")
>>> y = MyClass(foo="foo", bar="bar")
>>> x == y
True
