Topic 01: Introduction to Python

🎯 Learning Objectives

Explain what an algorithm and a program are
Write and run a simple Python program
Declare variables and assign values
Identify the basic Python data types: int, float, str, bool, None
Use print() and input() for basic I/O
Use the type() function to check a value's type

📚 Key Concepts

Algorithm vs Program

An algorithm is a step-by-step plan (in human language or pseudocode) for solving a problem. A program is the algorithm written in a programming language (like Python) that a computer can execute.

Why Python?

Python is simple to read, widely used in data science, AI and engineering, and is an object-oriented language. It is interpreted — you can run code line by line in the Python shell (IDLE) or run a .py file.

Variables

A variable is a named storage location in memory. You create a variable by assigning a value with =.

name = "Alice"
age  = 20
gpa  = 3.8
is_enrolled = True

Variable names: start with a letter or _, no spaces, case-sensitive (Age ≠ age).

Python Data Types

Type	Example	Description
`int`	`42`	Whole number
`float`	`3.14`	Decimal number
`str`	`"hello"`	Text (in quotes)
`bool`	`True` / `False`	True or False
`NoneType`	`None`	No value / absence of value

Every value in Python is an object of some class. Use type(x) to check.

print() — Output

print("Hello, World!")        # Hello, World!
print("Name:", name)          # Name: Alice
print(age, gpa)               # 20 3.8
print("Sum:", 3 + 4)          # Sum: 7

input() — User Input

input() always returns a string. Convert it if you need a number.

name = input("Enter your name: ")
age  = int(input("Enter your age: "))
gpa  = float(input("Enter GPA: "))

Comments

Use # for single-line comments. Comments are ignored by Python — they explain the code to humans.

# This is a comment
x = 5   # inline comment

type() and isinstance()

x = 42
print(type(x))            # <class 'int'>
print(type("hello"))      # <class 'str'>
print(isinstance(x, int)) # True

💻 Code Examples

Example 1 — First program

# A simple Python program
print("Welcome to ICT582!")
name = input("What is your name? ")
print("Hello,", name)

Example 2 — Variables and types

age   = 21
height = 1.75
name  = "Bob"
active = True

print(type(age))     # <class 'int'>
print(type(height))  # <class 'float'>
print(type(name))    # <class 'str'>
print(type(active))  # <class 'bool'>

Example 3 — Input and simple calculation

price = float(input("Enter price: "))
qty   = int(input("Enter quantity: "))
total = price * qty
print("Total:", total)

⚠️ Exam Focus

Know the difference between an algorithm and a program — expect a definition question.
Be able to identify what data type a value is (int, float, str, bool).
Know that input() always returns a str — you must convert it with int() or float() to do arithmetic.
Write a short program that takes user input and prints output — a common exam question.
Know that Python is an object-oriented language and every value is an object.

❌ Common Mistakes

Forgetting to convert input() — int(input(...)) is needed for arithmetic; without it you get string concatenation not addition.
Using undefined variables — you must assign before using: x = 5 before printing x.
Case errors — True and False must start with capital T/F; true causes a NameError.
Mixing tabs and spaces for indentation — Python is strict; use spaces consistently.

⚡ Quick Recap

An algorithm is a plan; a program is the algorithm written in Python.
Python's basic types: int, float, str, bool, None.
print() outputs; input() reads user text (always a string).
Use int() or float() to convert user input for arithmetic.
Use type(x) to check a variable's type.
Comments start with # and are ignored by Python.

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