Introduction to Python

Python is a general-purpose programming language designed to be readable. It is used for data analysis, web servers, automation scripts, machine learning and scientific work, and it is the language most often recommended to people who have never programmed before — because you can write something useful on your first day.

Why it reads the way it does#

Compare the same idea in two languages:

// Java
public class Main {
    public static void main(String[] args) {
        System.out.println("Hello");
    }
}

# Python
print("Hello")

Python removes ceremony that other languages require: no class wrapper for a script, no type declarations, no semicolons, no braces. Indentation defines structure, which forces the code to be laid out the way it reads.

That design has a cost. Python is slower than compiled languages, and mistakes that a compiler would catch in Java or C# surface only when the line actually runs. For most work the trade is worth it; for a real-time game engine it is not.

What people build with it#

Where it is a poor fit: mobile apps, browser front ends (that is JavaScript), and anything where every millisecond counts.

Installing it#

Download the latest Python 3 from python.org. On Windows, tick Add python.exe to PATH during installation — skipping that box is the single most common setup problem.

python --version
python3 --version      # macOS and Linux often need the 3

macOS ships with an old Python for system use. Install your own rather than relying on it.

Your first program#

Save this as hello.py and run python hello.py from the same folder:

name = input("What is your name? ")
print(f"Hello, {name}!")

years = int(input("How old are you? "))
print(f"In ten years you will be {years + 10}.")

Four lines, and it already reads input, converts a type and formats output. That immediacy is a large part of why Python is recommended first.

What the language looks like#

# Variables - no type declarations
name = "Ana"
age = 34
price = 12.99
is_member = True

# Conditions - indentation defines the block
if age >= 18:
    print("adult")
elif age >= 13:
    print("teenager")
else:
    print("child")

# Loops
for fruit in ["apple", "pear", "plum"]:
    print(fruit)

for i in range(5):
    print(i)

# Functions
def average(numbers):
    if not numbers:
        return 0
    return sum(numbers) / len(numbers)

# Lists and dictionaries
scores = [88, 72, 95]
person = {"name": "Ana", "age": 34}

# Building a new list from an old one
passing = [s for s in scores if s >= 70]

The batteries-included library#

A great deal comes with Python and needs no installation:

from pathlib import Path
import json, csv, sqlite3, datetime, random, re

Path("data").mkdir(exist_ok=True)
print(json.dumps({"ok": True}))
print(datetime.date.today())
print(random.choice(["a", "b", "c"]))

Learning what is already in the standard library saves more time than any single other habit — a surprising number of small libraries exist to do something Python already does.

Installing packages#

python -m venv .venv

source .venv/bin/activate        # macOS and Linux
.venv\Scripts\activate           # Windows

python -m pip install requests
python -m pip freeze > requirements.txt

Make a virtual environment per project from the very beginning. It keeps each project’s packages separate, and it prevents the single most common category of beginner error — imports failing because the package went somewhere else.

How it compares#

Learning one makes the next much easier. Loops, functions and conditions are the same ideas everywhere; only the punctuation changes.

What to learn, in order#

1. Variables and types — strings, numbers, booleans
2. Conditions — if, elif, else
3. Loops — for and while
4. Lists and dictionaries
5. Functions — and returning values rather than printing
6. Files — reading and writing
7. Errors — try and except
8. Modules and virtual environments

Then pick a direction — pandas for data, Flask or Django for web, or automation for anything tedious you do by hand.

Where to go next#

• Python basics — the syntax in more depth.
• Python virtual environments — the habit to form early.
• Why is my Python code not working? — for the first errors you meet.