Python Keywords and Identifiers

Python Keywords and Identifiers

In this tutorial, you will learn about keywords (reserved words in Python) and identifiers (names given to variables, functions, etc.).

Python Keywords

Keywords are the reserved words in Python.

We cannot use a keyword as a variable name, function name or any other identifier. They are used to define the syntax and structure of the Python language.

In Python, keywords are case sensitive.

There are 33 keywords in Python 3.7. This number can vary slightly over the course of time.

All the keywords except True, False and None are in lowercase and they must be written as they are. The list of all the keywords is given below.

False await else import pass
None break except in raise
True class finally is return
and continue for lambda try
as def from nonlocal while
assert del global not with
async elif if or yield

Looking at all the keywords at once and trying to figure out what they mean might be overwhelming.

If you want to have an overview, here is the complete list of all the keywords with examples.


Python Identifiers

An identifier is a name given to entities like class, functions, variables, etc. It helps to differentiate one entity from another.

Rules for writing identifiers

  1. Identifiers can be a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore _. Names like myClass, var_1 and print_this_to_screen, all are valid example.
  2. An identifier cannot start with a digit. 1variable is invalid, but variable1 is a valid name.
  3. Keywords cannot be used as identifiers.
    global = 1
    Output
      File "<interactive input>", line 1
        global = 1
               ^
    SyntaxError: invalid syntax
  4. We cannot use special symbols like !, @, #, $, % etc. in our identifier.
    a@ = 0

    Output
      File "<interactive input>", line 1
        a@ = 0
         ^
    SyntaxError: invalid syntax
  5. An identifier can be of any length.

Things to Remember

Python is a case-sensitive language. This means, Variable and variable are not the same.

Always give the identifiers a name that makes sense. While c = 10 is a valid name, writing count = 10 would make more sense, and it would be easier to figure out what it represents when you look at your code after a long gap.

Multiple words can be separated using an underscore, like this_is_a_long_variable.