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Python Keywords and Identifiers

Python Keywords are the reserved words in Python while Python Identifiers are names given to entities like variables, functions, class etc.

Python Keywords​

Keywords are the reserved words in Python that have defined meanings.

You can't 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.

Python keywords are case sensitive.

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.

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

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

note

For example, there are 35 keywords in Python 3.8.

Note that the number of keywords can vary slightly over the course of time according to the Python version.

Python Identifiers​

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

Rules for writing identifiers​

  • 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.
  • An identifier can't start with a digit. 1variable is invalid, but variable1 is a valid name.
  • The first character of the variable must be a letter or an underscore ( _ ).
  • Keywords can't be used as identifiers. 
    global = 1
    File "<interactive input>", line 1
            global = 1
                   ^
    SyntaxError: invalid syntax
  • You can't use special symbols such as !, @, #, $, % etc. in the identifier name. 
    a@ = 0
     File "<interactive input>", line 1
        a@ = 0
         ^
    SyntaxError: invalid syntax
  • An identifier can be of any length.
  • Identifier names are case sensitive.

Important things to Remember​

The following are some tips to follow:

  • Python is a case-sensitive language. This means, Variable and variable are not the same.
  • Always assign identifiers a name that makes sense. This will save time and make it easier to understand what it represents when you look at the code after a long interval.
  • Multiple words can be separated using an underscore, like this_is_a_long_variable_identifier, or using camel-case notation, like thisIsALongVariableIdentifier

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