Python Tokens | Identifiers, Keywords, Variables and Constants

A Python program is made up of small building blocks called tokens. These are the smallest meaningful units of a program. Understanding tokens is essential because every Python statement is formed using different types of tokens such as keywords, identifiers, variables, constants, literals, and operators.

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What are Python Tokens?

Every Python program is created using a combination of different types of tokens.

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Types of Python Tokens

Token	Purpose
Keywords	Reserved words with predefined meanings.
Identifiers	Names given to variables, functions, classes, etc.
Variables	Store data values.
Constants	Values that are intended not to change.
Literals	Fixed values written directly in a program.
Operators	Perform operations on data.

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Keywords

Examples of Python Keywords

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

Note: The list of keywords may vary slightly with different Python versions.

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Identifiers

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Rules for Naming Identifiers

• Must begin with a letter (A-Z or a-z) or an underscore (_).
• Cannot begin with a digit.
• Can contain letters, digits, and underscores.
• Cannot contain spaces or special characters.
• Keywords cannot be used as identifiers.
• Python identifiers are case-sensitive.

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Examples of Valid Identifiers

```python student student_name marks1 _total age ```

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Examples of Invalid Identifiers

```python 1student student-name student name for class ```

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Variables

Examples

```python name = "Rahul" age = 16 marks = 92.5 ``` In the above program: - name, age, and marks are variables. - Their values can be modified later in the program.

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Naming Conventions for Variables

Convention	Example
Meaningful Name	student_name
Lowercase Letters	marks
Words Separated by Underscore	total_marks
Avoid Single Letters (except loops)	percentage instead of p

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Constants

Python does not provide a separate keyword for declaring constants. By convention, constant names are written using uppercase letters.

Example

```python PI = 3.14159 MAX_MARKS = 100 SCHOOL_NAME = "CodeStep Academy" ```

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Variables vs Constants

Variables	Constants
Value can change.	Value should not change.
Usually written in lowercase.	Usually written in uppercase.
Created during program execution.	Defined once and reused.

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Example Program

```python PI = 3.14 radius = 7 area = PI * radius * radius print("Area =", area) ``` Output ```text Area = 153.86 ```

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Real-Life Examples

Situation	Variable	Constant
School Result	student_marks	MAX_MARKS
Bank Account	balance	MIN_BALANCE
Circle Area	radius	PI

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Common Errors

Mistake	Correct Concept
Using a keyword as an identifier.	Keywords cannot be used as variable names.
Starting an identifier with a digit.	Identifiers cannot begin with numbers.
Using spaces in variable names.	Use underscores instead.
Assuming Python has a constant keyword.	Python follows the uppercase naming convention for constants.

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Quick Revision

Concept	Remember
Token	Smallest meaningful unit of a program
Keyword	Reserved word
Identifier	User-defined name
Variable	Stores changing values
Constant	Intended to remain unchanged

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CBSE Exam Tips

• Learn the rules for naming identifiers.
• Remember that keywords cannot be used as identifiers.
• Differentiate clearly between variables and constants.
• Write meaningful variable names in your programs.
• Practice identifying valid and invalid identifiers.

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Summary

Python programs are built using tokens such as keywords, identifiers, variables, constants, literals, and operators. Keywords have predefined meanings, identifiers are user-defined names, variables store data that can change, and constants represent values that are intended to remain fixed. Understanding these fundamental concepts is essential for writing clear, readable, and error-free Python programs.