Python Create Constant Variable: A Beginner Guide

Python has not defined a constant variable data type, however, we can use other way to implement it. In this tutorial, we will discuss how to create a constant variable in python.

What is constant variable

If a variable is constant, which means the value of this variable can not be changed or edited.

How to create a constant variable in python?

We provides two methods to create python constant variable.

Method 1: Create a python class to make the property cannot be edited.

Here is an example.

class Constant(object):
    def __init__(self, val):
        super(Constant, self).__setattr__("value", val)
    def __setattr__(self, name, val):
        raise ValueError("Trying to change a constant value", self)

Then you can use this Constant class to create a python constant variable.

PI = Constant(3.14)
print(PI.value)

PI.value = 3.1415926
print(PI.value)

Run this code, you will find PI = 3.14. However, if you assign a new value to PI, it will report error.

Method 2: Use python pconst library

Python pconst library can allow us to create a python constant variable.

To use it, you should install this library first.

pip install pconst

How to create a python constant variable using pconst?

Here is an example:

from pconst import const

const.PI = 3.14
print(const.PI)

const.PI = 3.1415926
print(const.PI)

We have created a python constant variable const.PI, we can not change its value.

Run this code, you will find this result.