为什么在这种方法中不使用`self`? [英] Why is `self` not used in this method?

问题描述

我的印象是 Python 类中的方法总是需要 self 参数(我知道它实际上不必是 self代码>，只是一些关键字).但是，我写的这个类不需要它:

I was under the impression that methods within Python classes always require the self argument (I know that it doesn't actually have to be self, just some keyword). But, this class that I wrote doesn't require it:

import ZipFile
import os
class Zipper:
    def make_archive(dir_to_zip):
        zf = zipfile.ZipFile(dir_to_zip + '.zip', 'w')
        for filename in files:
            zf.write(os.path.join(dirname, filename))
        zf.close()

看到了吗?没有self.当我在 make_archive 中包含一个 self 参数时，我得到一个 TypeError: make_archive() missing one positional argument 错误.为了弄清楚为什么会发生这种情况，我实际上是从文档中复制并尝试运行一个类似的程序:

See? No self. When I include a self argument to make_archive, I get a TypeError: make_archive() missing one positional argument error. In my search to figure out why this is happening, I actually copied and tried to run a similar program from the docs:

class MyClass:
    """A simple example class"""
    i = 12345

    def f(self):
        return 'hello world'

print(MyClass.f())  # I added this statement to have a call line

我得到了同样的错误！

TypeError: f() missing 1 required positional argument: 'self'

在包含 Zipper() 类的同一个模块中，我有多个类都使用了 self.我不明白这里的理论，这使得很难知道什么时候做什么，特别是因为程序直接从文档中复制 (这是文档页面) 在我运行时失败.我在 Debian Linux 上使用 Python 3.5 和 3.4.我唯一能想到的是它是一个静态方法(如果您在 @staticmethod 上面包含 @staticmethod，上面写的 Zipper.make_archive()>make_archive 方法)，但我找不到一个很好的解释来确定.

In the same module that contains the Zipper() class, I have multiple classes that all make use of self. I don't understand the theory here, which makes it difficult to know when to do what, especially since a program copied directly from the docs (this is the docs page) failed when I ran it. I'm using Python 3.5 and 3.4 on Debian Linux. The only thing that I can think of is that it's a static method (and the Zipper.make_archive() as written above works fine if you include @staticmethod above the make_archive method), but I can't find a good explanation to be sure.

推荐答案

您正试图将其用作静态方法.在你的例子中；

You are trying to use it as a static method. In your example;

class MyClass:
    """A simple example class"""
    i = 12345

    def f(self):
       return 'hello world'

a = MyClass()
a.f()  # This should work.

调用 MyClass.f() 假定 f 对于 MyClass 是静态的.您可以将其设为静态:

Calling MyClass.f() assumes f is static for MyClass. You can make it static as:

class MyClass:
    @staticmethod
    def f():  # No self here
       return 'hello world'

MyClass.f()

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