Variables in Python

Variable

A variable is a name given to a memory location that stores a value.

🔹 Correction: In Python, a variable does not directly represent the memory location itself; rather, it references an object stored in memory.

Example:

age=20
name="Ali"

Here:

• age stores the value 20
• name stores the value "Ali"

Variable Naming Conventions

These are the rules that must be followed when naming variables.

Rules

• Variable names can contain:
  • letters (a-z, A-Z)
  • digits (0-9)
  • underscore (_)
• A variable cannot start with a digit

❌ Invalid:

2age=20

✔ Valid:

age2=20

• We cannot use Python keywords as variable names.

🔹 Correction: Keywords are reserved words, not names with spaces.

Example keywords:

if, else, for, while, class, def, return

❌ Invalid:

for =10

• Variable names cannot contain spaces

❌ Invalid:

student age

✔ Valid:

student_age

• Variable names cannot contain special characters

❌ Invalid:

age@
price$

✔ Valid:

age
price_value

Best Practices for Naming Variables

To write clean and understandable code, programmers follow these practices:

1. Use descriptive names

Avoid unclear names like:

a=20

Better:

student_age=20

This makes the code easier to understand.

Naming Styles

There are different styles for writing variable names.

1. camelCase

The first word starts with lowercase, and every other word starts with a capital letter.

Example:

ageOfStudent=20

2. PascalCase

The first letter of every word is capitalized.

Example:

AgeOfStudent=20

🔹 Addition: PascalCase is often used for class names in Python, not variables.

3. snake_case

All letters are lowercase, and words are separated by _.

Example:

age_of_student=20

🔹 Important:

snake_case is the recommended style for variables and functions in Python (PEP 8 standard).

Structure of Statements

Example in Java:

inta=20;
intb=30;
intresult=a+b;

Explanation:

• a + b → expression
• a and b → operands
• + → operator
• The whole line → statement

🔹 Addition:

In Python, we write the same code without specifying the type:

a=20
b=30
result=a+b

This is because Python is a dynamically typed language.

Operators

An operator is a symbol that performs an operation on operands.

Example:

a+b

• a and b → operands
• + → operator

Boolean Expressions

A Boolean expression is an expression whose result is either:

• True
• False

Example:

a>b

Result:

• True if a is greater than b
• False otherwise

Relational Operators

Relational operators are used to compare two values.

Examples:

Example:

a=10
b=20
print(a < b) # True

Bitwise Operators

Bitwise operators work on the binary representation of numbers.

Steps of bitwise operation:

1. Convert numbers to binary
2. Apply the operation bit by bit

Example:

a=5 # 101
b=3 # 011
print(a&b) # 1

Symbols of Bitwise Operators

🔹 Correction: The NOT operator is ~, not -.

Difference Between Bitwise and Logical Operators

Logical Operators

Logical operators combine multiple conditions.

Comparison between Java and Python:

Example:

age=20
is_student=True

print(age>18andis_student)

Identity Operators

Python has two identity operators:

• is
• is not

These operators check whether two variables refer to the same object in memory.

Example:

a=20
b=20

print(a==b) # True (values are equal)
print(aisb) # True (same object in memory)

Example with different values:

c=30
print(aisc) # False

🔹 Important Note:

== compares values, while is compares object identity (memory reference).