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Your First Python Program

Launch Sprint · Day 4

Write your first Python program

You already installed Python and configured your IDE. Now it's time to create your first script, run it from the terminal, and understand what's happening under the hood.

Create hello.pyJump to debugging tips

2

Files created

Input · Output · Errors

Concepts

15 mins

Time

Create your script​

  1. Inside a new folder (e.g., python-playground), create and activate a virtual environment:
python -m venv .venv
source .venv/bin/activate  # Windows: .venv\Scripts\activate
  1. Create hello.py and add:
hello.pyBEGINNER
from datetime import datetime

def greet(name: str) -> str:
  timestamp = datetime.now().strftime("%H:%M:%S")
  return f"👋 Hello {name}! It's {timestamp}."


if __name__ == "__main__":
  user = input("What's your name? ")
  print(greet(user))

Functions keep logic reusable; the `__name__ == "__main__"` guard prevents code from running on import.

  1. Run it:
python hello.py

Understand stdin/stdout​

  • input() reads from standard input (terminal).
  • print() writes to standard output.
  • Redirect output into files using python hello.py > output.txt.

Add arguments​

Upgrade to argparse so your script accepts flags:

Adding CLI argumentsBEGINNER
import argparse
from datetime import datetime

parser = argparse.ArgumentParser(description="Greets a user.")
parser.add_argument("--name", default="Developer")
args = parser.parse_args()

now = datetime.now().strftime("%H:%M:%S")
print(f"Hi {args.name}, time is {now}")

Call with `python hello.py --name Ada`.

Debug it​

Set breakpoints in your IDE or run:

python -m pdb hello.py

Commands:

CommandDescription
nNext line
sStep into function
cContinue execution
p variableInspect value

Common errors​

ErrorFix
ModuleNotFoundError: No module named 'datetime'Activate your virtual environment; ensure Python standard library is accessible.
Permission denied on scriptRemove BOM or ensure file is not marked read-only (Windows).
Output encoding issuesUse UTF-8 terminal or remove emoji from output.

Next up in your learning path

Master Python syntax

Scale up by understanding whitespace, comments, and style.

Fundamentals

Explore variables & data types

Review the core data model from ints to strings.

Reference

Troubleshoot your environment

Re-run the installer checklist if scripts fail.

Setup

Frequently Asked Questions

Where should I save my Python files?

Create a dedicated projects folder (e.g., `~/code/python/`). Each project should have its own virtual environment and `README`.

Why use a virtual environment?

Virtual environments isolate dependencies per project so packages never conflict and deployments remain reproducible.

Can I run Python scripts without the terminal?

Yes. Most IDEs let you run scripts with a click, but always learn the CLI to work comfortably on servers and CI pipelines.