What is identifier in python?

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.

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 "", line 1
       global = 1
              ^
   SyntaxError: invalid syntax

4. We cannot use special symbols like !, @, #, $, % etc. in our identifier.

   a@ = 0

   
   Output

     File "", 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.

Table of Contents

• Python Keywords
• Python Identifiers
  • Rules for writing identifiers
  • Things to Remember

A Python identifier is a name used to identify a variable, function, class, module or other object. An identifier starts with a letter A to Z or a to z or an underscore [_] followed by zero or more letters, underscores and digits [0 to 9].

Python does not allow punctuation characters such as @, $, and % within identifiers. Python is a case sensitive programming language. Thus, Manpower and manpower are two different identifiers in Python.

Here are naming conventions for Python identifiers −

• Class names start with an uppercase letter. All other identifiers start with a lowercase letter.
• Starting an identifier with a single leading underscore indicates that the identifier is private.
• Starting an identifier with two leading underscores indicates a strongly private identifier.
• If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.

Updated on 24-Jan-2020 11:10:50

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