Python的函数是对象， [英] Python 'Functions are objects'

问题描述

我总是听到这个声明在Python（对于主题，如装饰器等，当你传递函数，等），但从来没有真正看到这方面的细节。

I always hear this statement in python (for topics such as decorators, etc. when you are passing functions, etc.) but have never really seen an elaboration on this.

例如，可以创建一个只有一个抽象方法的类 c

For example is it possible to create a class c that has only one abstract method that is called with a set of opened and closed brackets.

i.e class c:
       @abstractmethod
       def method_to_be_called_by():
        ... 

以便您可以拥有

c(whatever parameters are required)

（我不会是第一次，也不会是最后一次），我只是好奇这个

I could be way off the mark with my understanding here(wouldn't be the first time and won't be the last), I was just curious about what people meant by this

推荐答案

您正在查找 __ call __ 方法。函数对象有这种方法：

You are looking for the __call__ method. Function objects have that method:

>>> def foo(): pass
... 
>>> foo.__call__
<method-wrapper '__call__' of function object at 0x106aafd70>

不是说Python解释器循环实际上在遇到Python函数对象时使用该方法;

Not that the Python interpreter loop actually makes use of that method when encountering a Python function object; optimisations in the implementation jump straight to the contained bytecode in most cases.

但你可以 在你自己的自定义类上使用：

But you can use that on your own custom class:

class Callable(object):
    def __init__(self, name):
        self.name = name

    def __call__(self, greeting):
        return '{}, {}!'.format(greeting, self.name)

演示：

>>> class Callable(object):
...     def __init__(self, name):
...         self.name = name
...     def __call__(self, greeting):
...         return '{}, {}!'.format(greeting, self.name)
... 
>>> Callable('World')('Hello')
'Hello, World!'

当您使用 创建函数对象 > def 语句，或，您可以使用 lambda 表达式：

Python creates function objects for you when you use a def statement, or you use a lambda expression:

>>> def foo(): pass
... 
>>> foo
<function foo at 0x106aafd70>
>>> lambda: None
<function <lambda> at 0x106d90668>

您可以将其与使用文字语法创建字符串或整数或列表进行比较：

You can compare this to creating a string or an integer or a list using literal syntax:

listobject = [1, 'two']

上面的代码创建了3个对象而不调用某个类型，Python根据所使用的语法为您创建了所有对象。这同样适用于函数。

The above creates 3 objects without ever calling a type, Python did that all for you based on the syntax used. The same applies to functions.

创建一个自己可以有点复杂;您需要有一个代码对象并引用一个全局命名空间，至少：

Creating one yourself can be a little more complex; you need to have a code object and reference to a global namespace, at the very least:

>>> function_type = type(lambda: None)
>>> function_type
<type 'function'>
>>> function_type(foo.__code__, globals(), 'bar')
<function bar at 0x106d906e0>

这里我通过重用函数类型，从 foo 函数获取代码对象;函数类型不是内置的名称，但类型确实存在，可以通过在现有函数实例上调用 type（）获得。

Here I created a function object by reusing the function type, taking the code object from the foo function; the function type is not a built-in name but the type really does exist and can be obtained by calling type() on an existing function instance.

我也在我的解释器的全局命名空间中传递了一个名字，后者是一个可选参数;则该名称将从代码对象中获取。

I also passed in the global namespace of my interpreter, and a name; the latter is an optional argument; the name is otherwise taken from the code object.

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