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A Python for loop runs a block of code once for each item in a sequence, such as a list, a string, a range of numbers or a dictionary. The loop variable takes each value in turn, so you never manage an index yourself: All the output on this page is real, from Python 3.12.5 … Read more >>
Do-while loops don’t exist in Python, but a while True loop that checks the condition at the bottom and exits with break does the same job. The body always runs at least once, just like a do-while in C, Java or JavaScript. The screenshots come from Python 3.12.5 in a real Command Prompt, typed answers … Read more >>
While loops in Python repeat a block of code as long as a condition stays true. Python checks the condition before every pass, so a Python while loop is the right choice when you don’t know in advance how many times it should run. The examples use US dollars and ZIP codes, and each one … Read more >>
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 >>