Constant variable the name itself says that it is constant. We have to define a constant variable at the time of declaration. After that, we will not able to change the value of a constant variable. In some cases, constant variables are very useful.
Creating constant variables, functions, objects is allowed in languages like c++, Java. But in python creating constant variable, it is not allowed. There is no predefined type for a constant variable in Python. But we can use pconst library for that.
Installation:
pip install pconst
Below are some examples which depict how to use constants in python
Example 1:
You can set constants to const module’s attribute.
Python3
# import module from pconst import const # declare constants const.LANGUAGE = "PYTHON"const.COMPANY_NAME = 'GFG' # display print(const.LANGUAGE) print(const.COMPANY_NAME) |
Output:
Example 2:
If try to update the constant value, ConstantError will be raised.
Python3
# import module from pconst import const # declare constants const.LANGUAGE = "PYTHON"const.COMPANY_NAME = 'GFG' # update const.LANGUAGE="C++" |
Output:
Example 3:
The del operator is disallowed.
Python3
# import module from pconst import const # declare constants const.LANGUAGE = "PYTHON"const.COMPANY_NAME = 'GFG' # delete del const.LANGUAGE |
Output:
Example 4:
You can also set dict and list value to const module, and they will be not editable (if dict or list values contains dict or list, then will be applied recursively.).
Python3
# import module from pconst import const # define dictionary const.COMPANY_DATA = { 'Name': "GFG", 'Language': ["C", "C++", "Python"]} # display print('Name:', const.COMPANY_DATA['Name']) print('Language:', const.COMPANY_DATA['Language']) |
Output:
