How do I create a constant in Python?

python constants
zfranciscus picture zfranciscus · Apr 21, 2010 · Viewed 1M times · Source

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";

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

Answer

Felix Kling picture Felix Kling · Apr 21, 2010

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

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

class Foo(object):
    CONST_NAME = "Name"

if not, it is just

CONST_NAME = "Name"

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

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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