Class 11:Python Identifiers

Python Identifiers

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.


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 perfectly fine.

Keywords cannot be used as identifiers.

>>>a=10 (valid)
>>>class=10 (invalid)
>>> global = 1(invalid)
File “<interactive input>”, line 1
global = 1
SyntaxError: invalid syntax

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

>> a@ = 0 invalid)
>>>a$=10 (invalid)
>>>a#=20 (invalid)
File “<interactive input>”, line 1
a@ = 0
SyntaxError: invalid syntax

3. Identifier can be of any length.


Things to care about

* Python is a case-sensitive language. This means, Variable and variable are not the same. Always name identifiers that make sense.

* While, c = 10 is valid. Writing count = 10 would make more sense and it would be easier to figure out what it does even when you look at your code after a long gap.

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

* We can also use camel-case style of writing, i.e., capitalize every first letter of the word except the initial word without any spaces. For example: camelCaseExample


A fixed numeric or non numeric value is called a literal. It can be defined as a number, text or other data that represents values to be stored in variables.
Examples of literals are 2, -45, 76.89, “abc”, “xyz”, “Hello hi”, ‘abc’ etc.


Delimiters are the symbols which can be used as separators of values or to enclose some values.
Examples of delimiers are: () {} [] , / ; etc.