Python Programming Tutorials

Python’s break and continue both change how a loop runs. break exits the loop immediately, and continue skips the rest of the current pass and moves on to the next one. Both work in for and while loops. The orders, statuses and seat numbers below are made up, but every output is real: I ran … Read more >>

pip installs a specific version when you put == and the version number after the package name. The same command downgrades or upgrades whatever’s already installed: I tested every command below in a real Windows Command Prompt with Python 3.12.5 and pip 24.2, inside a separate environment so you can see each install happen from … Read more >>

ModuleNotFoundError after pip install almost always means pip installed the package for one Python, and you ran your code with a different one. The fix is to install with the exact interpreter that runs your script: Every screen below is a real Command Prompt on Windows with Python 3.12.5, using two separate environments so you … Read more >>

Mutable vs immutable in Python comes down to one question: can the object change after it’s created? Lists, dictionaries and sets are mutable, so they change in place. Strings, ints, floats and tuples are immutable, so every “change” builds a new object. I ran each snippet on Python 3.12.5, and the screenshots are the real … Read more >>

UnboundLocalError (“local variable referenced before assignment”) means a function reads a variable that Python has decided is local, before that local variable has been given a value. It almost always happens because the function assigns to a name that also exists outside it. Newer versions of Python, including the Python 3.12.5 I used for every … Read more >>

Scope decides where a Python variable can be seen: a name created inside a function is local, and a name at the top of a file is global. Python looks names up in Local, Enclosing, Global, then Built-in scope, the LEGB rule. These examples ran on Python 3.12.5, and the screenshots come straight from the … Read more >>

Recursion in Python is when a function calls itself to solve a smaller version of the same problem. Every recursive function needs a base case that stops the calls and a recursive case that moves toward it; without a base case Python stops with RecursionError after about 1,000 calls. This guide shows how Python recursion … Read more >>

Regular expressions in Python are patterns for finding, checking, extracting and replacing text, and they are provided by the built-in re module. re.search(r”\d+”, text) finds the first number in a string, re.findall() returns every match, and re.sub() replaces them. This guide covers every re function, the pattern syntax, groups, greedy and lazy matching, flags, lookarounds, … Read more >>