Introduction and Getting Started
What You'll Learn
By the end of this lesson you will be able to install Python, open a terminal, and run your first Python program.
Why Python?
Python is one of the most beginner-friendly programming languages in the world. It uses plain English words, and you can get something working in minutes.
Python is used for:
- Web development (Instagram, Pinterest)
- Data science and AI (ChatGPT, self-driving cars)
- Automation (renaming files, sending emails, scraping websites)
- Server scripts (managing Linux servers, cron jobs)
Step 1 — Check If Python Is Already Installed
Open your terminal and type:
python3 --version
If you see something like Python 3.11.4, you're ready. Skip to Step 3.
Step 2 — Install Python
Linux (Ubuntu/Debian):
sudo apt update
sudo apt install python3 python3-pip -y
macOS:
brew install python3
Windows: Download the installer from python.org and check "Add Python to PATH" during installation.
Step 3 — Write Your First Program
Create a file called hello.py:
print("Hello, World!")
Run it:
python3 hello.py
Output:
Hello, World!
🎉 Congratulations — you just ran your first Python program!
Step 4 — Try the Python REPL
The REPL (Read-Evaluate-Print Loop) lets you run Python one line at a time. Start it:
python3
You'll see >>>. Type:
>>> print("Hello!")
Hello!
>>> 2 + 2
4
>>> exit()
Type exit() to quit the REPL.
How Python Programs Work
You write code in a .py file
↓
Python reads and runs each line top to bottom
↓
Results appear in the terminal
Python is an interpreted language — it doesn't need to be compiled before running. This makes it fast to experiment with.
Your First Multi-Line Program
# This is a comment — Python ignores lines starting with #
name = "Alice"
age = 25
print("Name:", name)
print("Age:", age)
print("In 10 years:", age + 10)
Output:
Name: Alice
Age: 25
In 10 years: 35
Common Mistakes
| Mistake | Error You'll See | Fix |
|---|---|---|
Typing python instead of python3 | command not found | Use python3 on Linux/Mac |
Forgetting parentheses in print | SyntaxError | Write print("hello"), not print "hello" |
| Wrong quotes | SyntaxError | Use " or ' consistently, not mixed |
| Typos in filenames | No such file | Check spelling with ls first |
Quick Reference
# Run a file
# python3 filename.py
# Print text
print("Hello!")
# Print a number
print(42)
# Print multiple things
print("Age:", 25)
# Comment a line (Python ignores it)
# This is a comment
Practice Exercises
- Hello You: Change
"Hello, World!"to print your own name. - Math: Write a program that prints the result of
100 * 365. - Multi-line: Write a program with 3
print()statements that each print something different.