dawei
我似乎无法修补类实例的__call__方法(是的,我想修补单个实例,而不是所有实例).
以下代码：
class A(object):
def test(self):
return "TEST"
def __call__(self):
return "EXAMPLE"
a = A()
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))
a.__call__ = lambda : "example"
a.test = lambda : "test"
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))
print(a())
print("Explicit call: {0}".format(a.__call__()))
print(a.test())
输出：
call method: <bound method A.__call__ of <__main__.A object at 0x7f3f2d60b6a0>> test method: <bound method A.test of <__main__.A object at 0x7f3f2d60b6a0>> call method: <function <lambda> at 0x7f3f2ef4ef28> test method: <function <lambda> at 0x7f3f2d5f8f28> EXAMPLE Explicit call: example test
虽然我想输出：
... example Explicit call: example test
我如何monkeypatch __call __()？为什么我不能像修补其他方法那样修补它？
虽然this answer告诉我们该怎么做(据说,我还没有测试过),但它没有解释为什么这个问题的部分原因.
解决方法
所以,正如
J.J. Hakala评论的那样,Python真正做的是调用：
type(a).__call__(a)
因此,如果我想覆盖__call__方法,我必须覆盖类的__call__,但如果我不想影响同一个类的其他实例的行为,我需要使用override__call__创建一个新类.方法.
所以如何覆盖__call__的示例如下所示：
class A(object):
def test(self):
return "TEST"
def __call__(self):
return "EXAMPLE"
def patch_call(instance,func):
class _(type(instance)):
def __call__(self,*arg,**kwarg):
return func(*arg,**kwarg)
instance.__class__ = _
a = A()
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))
patch_call(a,lambda : "example")
a.test = lambda : "test"
print("call method: {0}".format(a.__call__))
print("test method: {0}".format(a.test))
print("{0}".format(a()))
print("Explicit a.__call__: {0}".format(a.__call__()))
print("{0}".format(a.test()))
print("Check instance of a: {0}".format(isinstance(a,A)))
运行它会产生以下输出：
call method: <bound method A.__call__ of <__main__.A object at 0x7f404217a5f8>> test method: <bound method A.test of <__main__.A object at 0x7f404217a5f8>> call method: <bound method patch_call.<locals>._.__call__ of <__main__.patch_call.<locals>._ object at 0x7f404217a5f8>> test method: <function <lambda> at 0x7f404216d048> example Explicit a.__call__: example test Check instance of a: True
