Variable names are identifiers used to refer to values stored in memory. Choosing valid and meaningful variable names is important because it makes programs easier to read, understand, and maintain.

Python follows a set of rules for naming variables. If these rules are violated, the program will produce a syntax error.

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Rules for Naming Variables #

A variable name:

• Can contain letters (A-Z, a-z)
• Can contain digits (0-9)
• Can contain the underscore (_)
• Must begin with a letter or an underscore (_)
• Cannot begin with a digit
• Cannot contain spaces
• Cannot contain special characters such as @, #, $, %, &, etc.
• Cannot be a Python keyword such as if, for, or while
• Is case-sensitive

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Example 1: Valid Variable Names #

main.py

name = "Alice"
age = 25
salary_2026 = 45000
_marks = 95

print(name)
print(age)
print(salary_2026)
print(_marks)

Output #

Alice
25
45000
95

Explanation #

The following are valid variable names:

• name begins with a letter.
• age begins with a letter.
• salary_2026 contains letters, digits, and an underscore.
• _marks begins with an underscore, which is allowed.

All these names follow Python’s naming rules.

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Example 2: Variable Names are Case-Sensitive #

main.py

name = "Alice"
Name = "Bob"
NAME = "Charlie"

print(name)
print(Name)
print(NAME)

Output #

Alice
Bob
Charlie

Explanation #

• name
• Name
• NAME

are three different variables.

Python treats uppercase and lowercase letters as different characters.

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Example 3: Variable Names Can Contain Numbers #

main.py

student1 = "Alice"
student2 = "Bob"

print(student1)
print(student2)

Output #

Alice
Bob

Explanation #

• Digits can appear in a variable name.
• However, they cannot appear as the first character.
• Appending numbers is useful when multiple similar variables are required.

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Example 4: Variable Names Can Contain Underscores #

main.py

first_name = "John"
last_name = "Smith"

print(first_name)
print(last_name)

Output #

John
Smith

Explanation #

• The underscore (_) is commonly used to separate words.
• This naming style is called snake_case.
• According to the Python style guide (PEP 8), variables should generally be written using snake_case.

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Example 5: Meaningful Variable Names #

main.py

radius = 5
area = 3.14 * radius * radius

print(area)

Output #

78.5

Explanation #

• radius clearly indicates what the value represents.
• area clearly describes the calculated result.
• Meaningful names make programs easier to understand.

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Example 6: Avoiding Single-Letter Variable Names #

main.py

employee_salary = 45000

print(employee_salary)

Output #

45000

Explanation #

Using descriptive names such as employee_salary is much better than using names like:

x
a
temp

Good names make code easier to read and maintain.

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Invalid Variable Names #

The following examples violate Python’s naming rules.

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Example 7: Variable Name Starting with a Digit #

Incorrect

1name = "Alice"

Output #

SyntaxError: invalid decimal literal

Explanation #

Variable names cannot begin with a number.

Correct

name1 = "Alice"

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Example 8: Variable Name Containing Spaces #

Incorrect

first name = "John"

Output #

SyntaxError: invalid syntax

Explanation #

Spaces are not allowed inside variable names.

Correct

first_name = "John"

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Example 9: Variable Name with Special Characters #

Incorrect

salary$ = 45000

Output #

SyntaxError: invalid syntax

Explanation #

Special characters such as:

• $
• @
• #
• %
• &

cannot be used in variable names.

Correct

salary = 45000

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Example 10: Using a Python Keyword #

Incorrect

for = 10

Output #

SyntaxError: invalid syntax

Explanation #

for is a reserved keyword in Python.

Keywords have predefined meanings and cannot be used as variable names.

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Common Mistakes #

1. Starting a Variable Name with a Number #

Incorrect

2marks = 90

Correct

marks2 = 90

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2. Using Spaces in Variable Names #

Incorrect

student name = "Alice"

Correct

student_name = "Alice"

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3. Using Special Characters #

Incorrect

price@home = 500

Correct

price_home = 500

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4. Using Keywords as Variable Names #

Incorrect

if = 100

Correct

value = 100

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5. Using Meaningless Variable Names #

Poor Practice

x = 45000

Better Practice

employee_salary = 45000

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Best Practices #

• Use meaningful and descriptive variable names.
• Follow the snake_case naming convention.
• Keep variable names short but descriptive.
• Avoid abbreviations unless they are widely understood.
• Do not use Python keywords as variable names.
• Use lowercase letters for most variable names.

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Key Points to Remember #

• Variable names can contain letters, digits, and underscores.
• A variable name must begin with a letter or an underscore.
• Variable names cannot begin with a digit.
• Spaces and special characters are not allowed.
• Variable names are case-sensitive.
• Python keywords cannot be used as variable names.
• Use descriptive names to improve code readability.
• Follow the snake_case naming convention recommended by PEP 8.