Abstraction in Programming

• Abstraction helps hide complexity by:
• Breaking programs into smaller parts.
• Using black boxes that execute predefined steps.
• Using abstract concepts such as variables, data types, and expressions.
• Abstract algorithms can be reused for multiple purposes.

Variables and Data Types

What are Variables?

• Variables are containers that store values used in a program.
• Their values can change during execution.
• Constants differ as they remain unchanged during execution.

Rules for Naming Variables

✅ May contain letters, numbers, and underscores (_). ✅ Can be long or short. ✅ Are case-sensitive. ❌ Cannot start with a number. ❌ Cannot contain spaces. ❌ Cannot use Python reserved keywords.

Common Data Types

Data TypeDescriptionInteger (int)Whole numbersFloat (float)Decimal numbersString (str)Text or charactersBoolean (bool)True or False values

Data Structures

• List: Stores multiple values in a mutable structure ([]).
• Tuple: Stores multiple values in an immutable structure (()).

Boolean Expressions and Logical Operators

• Boolean expressions return True or False.
• Relational Operators:
• > (greater than), < (less than), >= (greater or equal), <= (less or equal)
• == (equal), != (not equal)
• Logical Operators:
• and (both conditions must be True)
• or (at least one condition must be True)
• not (negates a condition)

Checking and Converting Data Types

• Use type() to check a variable’s type.

print(type("Hello"))  # Output: <class 'str'>

• Convert data types when needed:

str(8)  # Converts integer 8 to string "8"
float(10)  # Converts integer 10 to float 10.0

Writing Output to a File

1. Create and write (overwrite) a file:

with open("example.txt", "w") as file:
    file.write("Hello, World!")

1. Open and append content:

with open("example.txt", "a") as file:
    file.write(" Adding new content.")

1. Write multiple lines:

with open("example.txt", "w") as file:
    file.write("Line 1\nLine 2\n")

Using Python Functions and Libraries

Built-in Functions

• Python has many pre-defined functions, e.g., print(), len(), max(), min().
• Example:

print(len("Hello"))  # Output: 5

• Full list: Python Built-in Functions

Using Python Libraries

• Libraries (or modules) contain reusable functions.
• Example:

import random
print(random.choice(["Apple", "Banana", "Cherry"]))

• Math Library provides useful functions:

import math
print(math.sqrt(16))  # Output: 4.0