如何测试一个对象是一个函数还是一个未绑定的方法？

def is_unbound_method(func):
    pass

def foo(): pass

class MyClass(object):
    def bar(self): pass

我可以在is_unbound_method的主体中放置什么呢？

is_unbound_method(foo) == False
is_unbound_method(MyClass().bar) == False
is_unbound_method(MyClass.bar) == True

??

解决方法:

未绑定的方法将__self__设置为None：

def is_unbound_method(func):
    return getattr(func, '__self__', 'sentinel') is None

演示：

>>> foo.__self__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute '__self__'
>>> is_unbound_method(foo)
False
>>> MyClass.bar.__self__
>>> is_unbound_method(MyClass.bar)
True
>>> MyClass().bar.__self__
<__main__.MyClass object at 0x106c64a50>
>>> is_unbound_method(MyClass().bar)
False

该属性也可用作.im_self,但__self__是向前兼容的.

请注意,在Python 3中,未绑定的方法已经消失;访问MyClass.bar返回函数对象.因此,上述函数将始终返回False.

请参阅用户定义方法部分中的Datamodel documentation：

Special read-only attributes: im_self is the class instance object, im_func is the function object

[…]

Changed in version 2.6: For Python 3 forward-compatibility, im_func is also available as __func__, and im_self as __self__.

[…]

When a user-defined method object is created by retrieving a user-defined function object from a class, its im_self attribute is None and the method object is said to be unbound.

标签：python,introspection
来源： https://codeday.me/bug/20190725/1530121.html