Question

MyClass及其实例在myModule.py中定义：

class MyClass(object):
    pass

obj = MyClass()

将function定义为obj的方法：

from myModule import obj
def function(msg):
    print msg

如何使用MyClass作为方法扩展function个实例？一种方式：

obj.function = function

但这与在类定义中定义的不一样，例如：

class MyClass(object):
    def __init__(self): 
        self.value = 'Value'

    def function(self, msg):
        print msg, self.value

将function定义为MyClass方法后，它可以访问类的属性，例如self.value。

Answer 1

我不知道你为什么要重复这个问题，因为wim和I都提供了不涉及子类化的解决方案。

当在MyClass定义中定义function（）时，它能够访问Class的一个或多个变量，例如self.value ....

我已经从你的另一篇文章中扩展了我的答案，以证明这已经成为现实：

from unittest import mock

# This class would be defined in some third-party library
class MyClass:
    def __init__(self):
        self._private_property = 'foo'

    def method(self, msg):
        print('from method:', msg)


def function(self, msg):
    print('Accessing private property from function:', self._private_property)
    print('from function:', msg)


old_method = MyClass.method


def new_method(self, msg):
    old_method(self, msg)
    function(self, msg)


# The patch is only applied within this scope
with mock.patch.object(MyClass, 'method', new_method):
    foo = MyClass()
    foo.method('message with patched')

# By this point MyClass is "back to normal"
print('---')
foo.method('message with original')

<强>输出

from method: message with patched
Accessing private property from function: foo
from function: message with patched
---
from method: message with original

Answer 2

class MyClass(object):
    def __init__(self): 
        self.value = 'value'

def function(self, msg):
    print 'msg:', msg, 'value:', self.value 

foo = MyClass()
foo.function = function.__get__(foo)
foo.function(msg = 'hello world')

如何在没有类继承的情况下扩展实例

2 个答案: