Lab 01: Hello World & Python Basics

🎯 Objective

Write and run your first Python program, understand the Python interpreter, and learn the basic building blocks of the language.

📚 Background

Python is an interpreted, high-level programming language created by Guido van Rossum in 1991. It's now the world's most popular language for data science, web development, and automation. Python code reads almost like English — making it ideal for beginners and experts alike.

⏱️ Estimated Time

20 minutes

📋 Prerequisites

• None — this is your first lab!

🛠️ Tools Used

• Python 3.12

🔬 Lab Instructions

Step 1: Your First Python Program

print("Hello, World!")
print("Welcome to Python 3.12")

📸 Verified Output:

Hello, World!
Welcome to Python 3.12

💡 print() is Python's built-in function for output. Unlike C or Java, no semicolons — Python uses newlines to end statements.

Step 2: Comments

# This is a single-line comment

"""
This is a multi-line string / docstring.
Used to document files, classes, and functions.
"""

x = 42  # The answer to everything
print(x)

📸 Verified Output:

42

Step 3: Python as a Calculator

print(2 + 3)     # Addition:       5
print(10 - 4)    # Subtraction:    6
print(3 * 7)     # Multiplication: 21
print(15 / 4)    # Division:       3.75 (always float)
print(15 // 4)   # Floor division: 3
print(15 % 4)    # Modulo:         3
print(2 ** 8)    # Exponent:       256

📸 Verified Output:

5
6
21
3.75
3
3
256

💡 / always returns float in Python 3. Use // for integer division. ** is the power operator.

Step 4: Variables

name = "Alice"
age = 30
height = 1.75
is_student = False

print(f"Name: {name}")
print(f"Age: {age}")
print(f"Type of age: {type(age)}")
print(f"Type of name: {type(name)}")

📸 Verified Output:

Name: Alice
Age: 30
Type of age: <class 'int'>
Type of name: <class 'str'>

💡 Python is dynamically typed — no need to declare types. f"..." is an f-string for embedding variables in text.

Step 5: Multiple Assignment and Swap

x, y, z = 1, 2, 3
print(x, y, z)

a, b = 10, 20
print(f"Before: a={a}, b={b}")
a, b = b, a   # Swap without temp variable!
print(f"After:  a={a}, b={b}")

📸 Verified Output:

1 2 3
Before: a=10, b=20
After:  a=20, b=10

Step 6: Print Function Options

# Custom separator
print("apple", "banana", "cherry", sep=", ")

# No newline at end
print("Same ", end="")
print("line!")

# Multiple values
print("Sum:", 3 + 4, "Product:", 3 * 4)

📸 Verified Output:

apple, banana, cherry
Same line!
Sum: 7 Product: 12

Step 7: Getting System Info

import sys
import platform

print(f"Python version: {sys.version_info.major}.{sys.version_info.minor}")
print(f"Platform: {platform.system()}")
print(f"Max integer: {sys.maxsize:,}")

📸 Verified Output:

Python version: 3.12
Platform: Linux
Max integer: 9,223,372,036,854,775,807

Step 8: Python's Philosophy

# Python emphasizes readability
# Bad (C-style):
x=10;y=20;z=x+y;print(z)

# Good (Pythonic):
x = 10
y = 20
z = x + y
print(z)

📸 Verified Output:

30
30

💡 Both work, but Python style (PEP 8) uses spaces around operators and one statement per line. Readable code is maintainable code.

✅ Verification

import sys
print(f"Python {sys.version_info.major}.{sys.version_info.minor} ✅")
print(f"2**10 = {2**10}")
print("Lab 1 verified ✅")

🚨 Common Mistakes

• Mixing tabs and spaces — use 4 spaces consistently

• Print() vs print() — Python is case-sensitive

• 5/2 returns 2.5 not 2 — use 5//2 for integer division

• Forgetting quotes around strings: name = Alice → NameError

📝 Summary

• print() outputs to the terminal; # starts a comment

• Variables assigned with =; no type declarations needed

• Core types: int, float, str, bool

• f-strings f"{value}" are the modern formatting standard

• Python enforces readability — clean code is Pythonic code

🔗 Further Reading

• Official Python Tutorial

• PEP 8 Style Guide