Introduction to Python

Python is a general-purpose language built around one idea: code is read far more often than it is written. Almost every decision in the language follows from that, and it is why Python reads close to the description of what it does.

Why people start here

Python asks very little of you before you can do something useful. There is no build step, no type declarations to satisfy, and no boilerplate around the thing you actually want to say.

print("Hello, world!")

That is the whole program. Save it as hello.py, run python hello.py, and you are running Python.

The shape of the language

Blocks are marked by indentation rather than braces, so how the code looks and what it means cannot disagree:

def greet(names):
    for name in names:
        if name:
            print(f"Hello, {name}!")

greet(["Ada", "Grace", "Alan"])

Four spaces to a level is the convention, and following it is the whole of the style debate.

Batteries included

Python ships with a large standard library, so a great deal is available before you install anything at all — JSON, dates, HTTP, file paths, databases, testing.

import json
from pathlib import Path

settings = json.loads(Path("settings.json").read_text())
print(settings["name"])

Where it is used

The same language covers a script that renames a folder of files, the back end serving this page, and the notebook training a model. That range is why learning Python once pays off in several directions at the same time.

What comes next

The tutorials that follow build from here: variables and types, control flow, functions, then the data structures that make Python feel like Python. Nothing below assumes anything you have not read above.