list()是否被视为函数? [英] Is `list()` considered a function?

问题描述

list显然是内置类型 Python.我在此问题下看到一条评论，该问题将list()称为内置函数.而且，当我们检查文档时，它确实包含在内置函数列表中，但文档再次指出:

list is obviously a built-in type in Python. I saw a comment under this question which calls list() a built-in function. And when we check the documentation, it is, indeed, included in Built-in functions list but the documentation again states:

列表实际上不是可变函数，而是可变的序列类型

Rather than being a function, list is actually a mutable sequence type

这带给我的问题是:list()被视为函数吗?我们可以将其称为内置函数吗?

Which brings me to my question: Is list() considered a function? Can we refer to it as a built-in function?

如果我们在谈论C ++，我会说我们只是在调用构造函数，但是我不确定constructor一词是否适用于Python(在这种情况下从未遇到过).

If we were talking about C++, I'd say we are just calling the constructor, but I am not sure if the term constructor applies to Python (never encountered its use in this context).

推荐答案

list是type，这意味着它在某处被定义为类，就像int和float一样.

list is a type, which means it is defined somewhere as a class, just like int and float.

>> type(list)
<class 'type'>

如果您在builtins.py中检查其定义(实际代码在C中实现)

If you check its definition in builtins.py (the actual code is implemented in C):

class list(object):
    """
    Built-in mutable sequence.

    If no argument is given, the constructor creates a new empty list.
    The argument must be an iterable if specified.
    """

    ...

    def __init__(self, seq=()): # known special case of list.__init__
        """
        Built-in mutable sequence.

        If no argument is given, the constructor creates a new empty list.
        The argument must be an iterable if specified.
        # (copied from class doc)
        """
        pass

因此，list()不是函数.就像任何对CustomClass()的调用一样，它只是在调用list.__init__()(带有一些与本讨论无关的参数).

So, list() is not a function. It is just calling list.__init__() (with some arguments which are irrelevant for this discussion) just like any call to CustomClass() is doing.

感谢@jpg添加注释:Python中的类和函数具有一个公共属性:它们都被视为 callables ，这意味着它们可以用()调用.有一个内置函数callable，它检查给定的参数是否可调用:

Thanks for @jpg for adding in the comments: classes and functions in Python have a common property: they are both considered as callables, which means they are allowed to be invoked with (). There is a built-in function callable that checks if the given argument is callable:

>> callable(1)
False
>> callable(int)
True
>> callable(list)
True
>> callable(callable)
True

在builtins.py中也定义了

callable:

def callable(i_e_, some_kind_of_function): # real signature unknown; restored from __doc__
    """
    Return whether the object is callable (i.e., some kind of function).

    Note that classes are callable, as are instances of classes with a
    __call__() method.
    """
    pass

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