What Is Python? How to Install It and Write Your First Program

Python is a programming language that reads almost like plain English, which makes it one of the best first languages you can learn. It's also a professional tool used by Google, Netflix, NASA and thousands of small businesses. In this first lesson you'll install it, write your first program and learn to read the error messages every programmer sees daily.

1. See what Python is for
2. Install Python and VS Code
3. Run hello.py
4. Learn to read errors
5. Build a store receipt

What you can do with Python

Python is a "general-purpose" language: the same skills carry over to very different jobs.

How a program works

A program is a list of instructions the computer carries out in order. Python is an interpreted language: a program called the interpreter reads your code line by line and runs it. There's no separate compile step, so you see results in seconds. Every program you write takes this trip:

1. Step 1You write the codeIn VS Code, inside a file that ends in .py.
2. Step 2You save the filePython runs what's saved on disk. If you forget to save, you run the old version.
3. Step 3The interpreter reads itFirst it checks the syntax: quotes, parentheses and indentation.
4. Step 4It runs line by lineTop to bottom: the order of the lines is the order things happen.
5. Step 5You get output or an errorYou see what you printed or, if something breaks, an error message that points to the line.

Installing Python

Option 1: Nothing to install (start today)

Google Colab (free with a Google account) runs Python in your browser. It's enough until lesson 8, where you'll work with files.

Option 2: Install Python on your computer (recommended)

1. Go to python.org → Downloads and get the latest stable release of Python 3.
2. On Windows, python.org now points you to the Python install manager, the new official installer. Once it's installed, the py command manages your Python versions (for example, py install 3.15). If you use the classic installer instead, check "Add python.exe to PATH" on the first screen before clicking "Install Now." It's the step people forget most often.
3. On macOS, run the downloaded .pkg installer.
4. On Linux, Python is usually preinstalled; check it in the terminal.

To confirm the installation, open a terminal (on Windows, PowerShell or Command Prompt; on a Mac, the Terminal app) and type:

python --version

You should see something like Python 3.15.x (3.13 or 3.14 is fine too: this course works on Python 3.10 or newer). On macOS and Linux the command may be python3.

If the terminal doesn't recognize the command

The most common installation error on Windows looks like this:

'python' is not recognized as an internal or external command,
operable program or batch file.

Windows doesn't know where Python lives because it isn't on the PATH (the folders where Windows looks for programs). Reinstall with "Add python.exe to PATH" checked, or use the install manager, then close and reopen the terminal. Meanwhile, try py --version.

The code editor

Install Visual Studio Code (free) and Microsoft's official "Python" extension: you get syntax colors, autocomplete and a ▶ button that runs the current file.

Your first program

Create a file named hello.py with this content:

print("Hello, world!")
print("I'm learning Python")

Save it and run it with VS Code's ▶ button or from the terminal, inside the file's folder:

python hello.py

Output:

Hello, world!
I'm learning Python

print() is a function: a named instruction that does something. This one displays whatever you put inside the parentheses. Text goes inside quotes, double or single, as long as you open and close with the same kind (the second line uses double quotes because the text contains an apostrophe).

Interactive mode: Python as a calculator

If you type just python in the terminal, you enter interactive mode (you'll see the >>> prompt). Each line runs as soon as you press Enter:

>>> 2 + 3
5
>>> 10 / 4
2.5
>>> 2 ** 10
1024
>>> 0.1 + 0.2
0.30000000000000004
>>> 4.35 * 100
434.99999999999994

Type exit() to leave. Surprised by the last two results? Computers store decimals in binary, and numbers like 0.1 or 4.35 have no exact binary version. Every language does this; it isn't a Python bug. You'll tidy the display with round() in the next lesson.

Comments: notes for humans

Everything after a # is a comment, and Python ignores it. Use comments to explain why the code does something, not to repeat what it obviously does:

# Price with sales tax for a store in Austin, Texas
price = 100
print(price * 1.0825)  # 8.25% combined state and local rate

Hands-on example: a hardware store receipt

With nothing more than print(), math and comments you can already build something useful. Main Street Hardware in Austin, Texas, wants a quick receipt that adds up a purchase and shows the sales tax. Unlike many countries, U.S. shelf prices usually don't include sales tax: it's added at the register. Create receipt.py:

# Receipt for Main Street Hardware (Austin, Texas)
# Prices don't include sales tax: it's added at checkout (8.25%)
print("=== MAIN STREET HARDWARE ===")
print("Duct tape     2 x $4.25 =", 2 * 4.25)
print("Light bulbs   3 x $3.90 =", 3 * 3.90)
print("Paint brush   1 x $9.50 =", 1 * 9.50)
subtotal = 2 * 4.25 + 3 * 3.90 + 1 * 9.50
print("Subtotal: $", round(subtotal, 2))
print("Sales tax (8.25%): $", round(subtotal * 0.0825, 2))
print("TOTAL: $", round(subtotal * 1.0825, 2))
print("Thanks for shopping with us!")

Output:

=== MAIN STREET HARDWARE ===
Duct tape     2 x $4.25 = 8.5
Light bulbs   3 x $3.90 = 11.7
Paint brush   1 x $9.50 = 9.5
Subtotal: $ 29.7
Sales tax (8.25%): $ 2.45
TOTAL: $ 32.15
Thanks for shopping with us!

Three details: subtotal = ... stores a result under a name so you can reuse it, which is a variable (next lesson); Python prints $ 29.7 instead of $29.70, which you'll fix in lesson 3; and the math checks out: $29.70 × 8.25% = $2.45 in tax, for a total of $32.15.

Indentation matters (a lot)

In Python, spaces at the start of a line aren't decoration: they tell Python which instructions belong to a block. You'll see this in detail with conditionals in lesson 4, but here's the rule for now: don't put spaces at the beginning of a line unless they belong there, or you'll get an IndentationError. The convention is 4 spaces per level, and VS Code inserts them for you when you press Tab.

Reading errors without fear

You're going to make lots of mistakes, and that's how everyone learns. The good news is that Python tells you exactly what went wrong and on which line. For example:

print("Hello)

  File "hello.py", line 1
    print("Hello)
          ^
SyntaxError: unterminated string literal (detected at line 1)

Read the message from the bottom up: the error type (SyntaxError), the explanation (a string that was never closed) and the line number. Here, the closing quote is missing.

Anatomy of a traceback

When an error happens while the program is running (not while Python is checking the syntax), you get a traceback, a trail of what Python was doing. Suppose that on line 3 of a receipt you typed pirnt:

Traceback (most recent call last):
  File "C:\python-course\receipt.py", line 3, in <module>
    pirnt("TOTAL")
    ^^^^^
NameError: name 'pirnt' is not defined. Did you mean: 'print'?

• File … line 3: the file and the exact line (Ctrl + click in VS Code takes you there).
• The line of code and the ^^^^^: they point at the part that failed.
• The last line: the error type, an explanation and even a suggestion: Did you mean: 'print'?

Lines 1 and 2 did run: Python stops at the first line that fails, so you may see part of your output and then the error.

Common beginner mistakes

Checklist before lesson 2

• python --version (or py --version) shows a 3.x version in the terminal.
• VS Code has the official "Python" extension installed.
• I ran hello.py from VS Code and from the terminal.
• I caused an error on purpose (deleted a quote) and could read its type and line.
• My hardware store receipt prints TOTAL: $ 32.15.

print("My name is Jordan")
print("I live in Columbus, Ohio")
# 7 days x 24 hours x 60 minutes
print(7 * 24 * 60)

Summary

• Python is an interpreted, readable and highly in-demand language used for automation, data, AI and web back ends.
• Install it from python.org (the install manager on Windows, or the classic installer with "Add python.exe to PATH") and use VS Code as your editor.
• print() displays information; # starts a comment for humans.
• Indentation has meaning in Python, and U.S. prices usually need sales tax added on top.
• Read a traceback from the bottom up: error type, explanation and exact line.

Next lesson: Python Variables, Data Types and Operators. You'll work with int, float, str and bool, convert between types and use arithmetic, comparison and logical operators.