Glossary

This glossary explains common Python terms in plain English. Each entry is a mini-reference: a one-line definition, a short explanation, a runnable example, the everyday tools that go with the term, and links to the lessons where you’ll use it.

Browse by category below, or jump straight to a term. New to programming? Start with Variable, String, List, Dictionary, and Function — they underpin almost everything else.

Start with these terms

Python basics

The building blocks every program is made of.

Variable: A name that refers to a stored value, so you can reuse it by name.
Syntax: The grammar rules for how Python code must be written.

Data types

The kinds of values Python works with.

String: A piece of text, written between quotes, e.g. "hello".
Integer: A whole number with no decimal point, e.g. 42.
Float: A number with a decimal point, e.g. 3.14.
Boolean: A value that is either True or False.
List: An ordered, changeable collection of items written in square brackets.
Tuple: An ordered, unchangeable sequence of values, written in parentheses, e.g. (3, 4).
Set: An unordered collection of unique items, written in braces, e.g. {1, 2, 3}.
Dictionary: A collection of key-value pairs for looking up values by key.

Control flow

How a program decides what to do and repeats work.

Conditional: Code that runs only when a condition is true (if / elif / else).
if statement: The statement that runs a block of code only when a condition is true.
Loop: Code that repeats, either over items (for) or while a condition holds (while).
for loop: A loop that runs once for each item in a sequence.
while loop: A loop that keeps repeating as long as a condition stays true.
Exception: An error raised while a program runs, which you can catch and handle.
try / except: A block that runs risky code and catches exceptions instead of crashing.

Functions

Reusable blocks of logic, and the tools built on them.

Function: A reusable, named block of code that can take inputs and return a result.
Parameter: A named variable in a function definition that receives an input value.
Argument: The actual value you pass to a function when you call it.
Return value: The value a function hands back to its caller with the return statement.
Lambda: A small anonymous function written in one line with the lambda keyword.
Decorator: A function that wraps another function to add behaviour, applied with the @name syntax above a def.
Generator: A function that produces a sequence of values lazily, one at a time, using yield instead of return.
Iterator: An object you can step through one item at a time with next(), until it is exhausted.

Object-oriented Python

Modelling things as objects with their own data and behaviour.

Class: A blueprint for creating objects that bundle data (attributes) with behaviour (methods).
Object: A single value built from a class, with its own attributes and methods. Also called an instance.
Method: A function that belongs to an object and is called on it with a dot, like text.upper().
Attribute: A piece of data stored on an object (or class), reached with a dot, like dog.name.
Inheritance: Defining a class that builds on another, reusing its attributes and methods.
Dunder method: A special method with double underscores, like __init__ or __str__, that Python calls automatically.

Files, data & scripting

Reading the world outside your program and running real scripts.

pathlib: Python's standard-library module for working with file and folder paths as objects.
File path: The location of a file or folder, as text or a pathlib Path object.
Module: A file of Python code you can import and reuse in other programs.
Import: The statement that loads a module or name so you can use it in your file.
Command-line argument: A value passed to a program on the command line when you run it, read in Python from sys.argv.
argparse: Python's standard-library module for building command-line interfaces that parse arguments and flags.
JSON: A text format for structured data, easily converted to and from Python objects.
CSV: A plain-text format for tabular data: one row per line, values separated by commas.
Context manager: An object used with the with statement that sets up and cleans up a resource automatically.

Tools & environment

Managing packages, versions, and confidence in your code.

Virtual environment: An isolated Python environment with its own installed packages, separate from the system Python.
pip: Python's package installer, used to add third-party libraries from PyPI.
Package: A folder of related modules you can import; also a library you install with pip.
requirements.txt: A text file listing a project's package dependencies, usually pinned to exact versions.
Version control: A system that records snapshots of your project over time so you can review and undo changes. Git is the most common.
Unit test: A small automated check that verifies one piece of code behaves as expected.

Web development

Serving pages and handling requests with a framework.

Web framework: A library that handles the plumbing of web requests so you can focus on your app's logic. Flask and Django are examples.
HTTP: The request/response protocol browsers and servers use to communicate on the web.
API: A defined way for programs to talk to each other and exchange data.
Route: A mapping from a URL path to the function that runs when someone visits it.
Template: An HTML file with placeholders that a web framework fills in with data before sending it to the browser.
HTML form: A part of a web page that collects input from the user and submits it to the server.
Static file: A file like CSS, JavaScript, or an image that the server sends to the browser unchanged.