Python Identifiers and Reserved keywords

In this article, we will discuss identifiers & reserved keywords in Python in detail

Identifiers :

  • name used to define variable
    • for example, x=10
  • name used to define method or function
    • for example, def f1():
  • name used to define class
    • for example, class Test(Exception):

Rules to define identifiers in Python:

  • Alphabets in uppercase (A-Z) & lowercase (a-z) and Digits (0 to 9) and Underscore (_) are allowed but no other special characters are allowed like $, #, etc.
  • Identifiers should start with alphabets and not with digits
  • Identifiers are case-sensitive i.e.; total & TOTAL are 2 different identifiers
  • Reserved or pre-defined keywords are not allowed to define identifiers
  • There is no upper limit on the length of characters for defining identifier in Python but it is not recommended to use long identifiers names as a programming practice

Identifiers starting with underscore:

  • If identifiers starts with single underscore (_) then it is considered as private
  • If identifiers starts with 2 continuous underscore (__) then it is considered as strongly private
  • If identifiers starts with 2 continuous underscore (__) and ends with 2 continuous underscore (__) then it is considered as language specific identifiers and it is special variable defined by Python itself

Reserved words:

There are 33 reserved keywords in Python,

  • Boolean values :- True, False, None
  • Logical operator :- and, or, not, is
  • Conditional statement :- if, else, elif
  • Flow controller :- while, for, break, continue, return, in, yield
  • Exception handling :- try, except, finally, raise, assert
  • Miscellaneous :- import, from, as, class, def, pass, global, nonlocal, lambda, del, with

Note :- all reserved keywords contains only lower-case alphabets except for Boolean values where starting letter is upper-case alphabet

How to list all reserved keywords in Python terminal ?

  • First we need to import keyword
  • Then invoke keyword.kwlist in the terminal
  • It prints all reserved keyword in square bracket

Happy Learning !!
Happy Coding !!

Python - Data Types
Introduction to Python programming