Python Variables

Introduction

• Variables in Python are used to store data that can be referenced and manipulated during program execution.
• Python variables do not require explicit declaration of type; the type is inferred based on the value assigned.
• Variables act as placeholders for data, allowing for storage and reuse of values.

Example

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Key Concepts

Rules for Naming Variables

• Variable names can contain letters, digits, and underscores (_).
• Cannot start with a digit.
• Case-sensitive (myVar and myvar are different).
• Avoid using Python keywords (e.g., if, else, for)._

Valid Example:

Invalid Example:

Assigning Values to Variables

• Use = operator to assign values.
• Dynamic Typing: A variable can hold different types of values during execution.

Example:

Multiple Assignments

• Assign the same value to multiple variables:

Output:

• Assign different values to multiple variables in one line:

Output:

Type Casting

• Convert one data type to another using functions like int(), float(), str().

Example:

Output:

Getting the Type of Variable

• Use type() function to determine the type.

Example:

Output:

Scope of a Variable

• Local Variables: Defined inside a function and accessible only there.
• Global Variables: Defined outside any function and accessible globally. Use global keyword to modify inside functions.

Example:

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Object Reference

• Variables hold references to objects, not the objects themselves.
• Reassigning a variable creates a new reference.

Deleting a Variable

• Use del keyword to remove a variable.

Example:

• Accessing x after deletion will raise NameError.

Practical Examples

Swapping Two Variables

• Swap values using multiple assignments.

Example:

Output:

Counting Characters in a String

• Use len() to find the length of a string.

Example:

Output:

This overview provides a foundational understanding of how variables work in Python, covering key principles such as naming conventions, value assignment, type casting, and variable scope.