How do I create a constant in Python?

Question

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

public static          


        

Answer 1

There's no perfect way to do this. As I understand it most programmers will just capitalize the identifier, so PI = 3.142 can be readily understood to be a constant.

On the otherhand, if you want something that actually acts like a constant, I'm not sure you'll find it. With anything you do there will always be some way of editing the "constant" so it won't really be a constant. Here's a very simple, dirty example:

def define(name, value):
  if (name + str(id(name))) not in globals():
    globals()[name + str(id(name))] = value

def constant(name):
  return globals()[name + str(id(name))]

define("PI",3.142)

print(constant("PI"))

This looks like it will make a PHP-style constant.

In reality all it takes for someone to change the value is this:

globals()["PI"+str(id("PI"))] = 3.1415

This is the same for all the other solutions you'll find on here - even the clever ones that make a class and redefine the set attribute method - there will always be a way around them. That's just how Python is.

My recommendation is to just avoid all the hassle and just capitalize your identifiers. It wouldn't really be a proper constant but then again nothing would.