如何在 Python 中创建常量?

问题描述

有没有办法在 Python 中声明一个常量?在 Java 中，我们可以通过这种方式创建常量值:

Is there a way to declare a constant in Python? In Java we can create constant values in this manner:

public static final String CONST_NAME = "Name";

上述Java常量声明在Python中的等价物是什么?

What is the equivalent of the above Java constant declaration in Python?

推荐答案

没有没有.您不能在 Python 中将变量或值声明为常量.只是不要改变它.

No there is not. You cannot declare a variable or value as constant in Python. Just don't change it.

如果您在课堂上，则相当于:

If you are in a class, the equivalent would be:

class Foo(object):
    CONST_NAME = "Name"

如果没有，那只是

CONST_NAME = "Name"

但您可能想看看代码片段 Python 中的常量 by Alex Martelli.

But you might want to have a look at the code snippet Constants in Python by Alex Martelli.

从 Python 3.8 开始，有一个 typing.Final 变量注释将告诉静态类型检查器(如 mypy)不应重新分配您的变量.这是最接近 Java 的 final 的等价物.但是，它实际上并不能阻止重新分配:

As of Python 3.8, there's a typing.Final variable annotation that will tell static type checkers (like mypy) that your variable shouldn't be reassigned. This is the closest equivalent to Java's final. However, it does not actually prevent reassignment:

from typing import Final

a: Final = 1

# Executes fine, but mypy will report an error if you run mypy on this:
a = 2

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