python - 如何包装(猴子补丁)@classmethod

Question

我想猴子修补一个类方法，保留旧功能。考虑我的代码来理解这个想法。这是我的代码(非常综合的例子)。

#!/usr/bin/env python

class A:

  @classmethod
  def foo(kls, param):
    print 'A.foo called, param is ' + param

  def bar(self, param):
    print 'A.bar called, param is ' + param


a = A()
a.foo('param_foo')
a.bar('param_bar')

# Patching things

def bar_wrapper(wrapped_func):
  def _w(*args, **kwargs):
    print '<bar_wrap>'
    wrapped_func(*args, **kwargs)
    print '</bar_wrap>'
  return _w

def foo_wrapper(wrapped_func):
  # Something missing here?
  def _w(*args, **kwargs):
    print '<foo_wrap>'
    wrapped_func(*args, **kwargs)
    print '</foo_wrap>'
  return _w

# Everything is pretty ok
A.bar = bar_wrapper(A.bar)
a.bar('is_is_wrapped?')

# Failed to wrap @classmethod
A.foo = foo_wrapper(A.foo)
A.foo('another_wrap_test')

这是我期望的输出:

A.foo called, param is param_foo
A.bar called, param is param_bar
<bar_wrap>
A.bar called, param is is_is_wrapped?
</bar_wrap>
<foo_wrap>
A.foo called, param is another_wrap_test
</foo_wrap>

这就是我得到的:

A.foo called, param is param_foo
A.bar called, param is param_bar
<bar_wrap>
A.bar called, param is is_is_wrapped?
</bar_wrap>
Traceback (most recent call last):
  File "./pytest.py", line 39, in <module>
    A.foo('another_wrap_test')
TypeError: unbound method _w() must be called with A instance as first argument (got str instance instead)

似乎有一个参数(类参数)在包装过程中丢失了。或者我只是没有装饰功能的想法？

提前致谢。

Answer 1

当您访问一个类的方法时，它在那一刻被包装；方法充当 descriptors在这里。

您可能想再次解包该方法，返回一个包装好的包装器:

def foo_wrapper(wrapped_func):
    wrapped_func = wrapped_func.__func__
    def _w(*args, **kwargs):
        print '<foo_wrap>'
        wrapped_func(*args, **kwargs)
        print '</foo_wrap>'
    return classmethod(_w)

现在返回的装饰器本身就是一个类方法，包装有效:

>>> class A:
...     @classmethod
...     def foo(kls, param):
...         print 'A.foo called, param is ' + param
... 
>>> def foo_wrapper(wrapped_func):
...     wrapped_func = wrapped_func.__func__
...     def _w(*args, **kwargs):
...         print '<foo_wrap>'
...         wrapped_func(*args, **kwargs)
...         print '</foo_wrap>'
...     return classmethod(_w)
... 
>>> A.foo = foo_wrapper(A.foo)
>>> A.foo('bar')
<foo_wrap>
A.foo called, param is bar
</foo_wrap>