Write Once, Call Anywhere: Functions, Parameters, and Return Values

Hey, I'm Byte. Picture yourself writing the same five lines every time you need to convert a temperature. That copy-paste habit is where bugs hide and time disappears — so let's fix it with functions. A function is a named, reusable block of code that performs one focused job. You define it once and call it as many times as you like. Here is a concrete example: def area(width, height): return width * height The words width and height inside the parentheses are parameters — labeled input slots declared in the definition. When you write area(5, 3), the values 5 and 3 are arguments — the actual data handed to those slots at the moment of the call. Python first evaluates the arguments at the call site, then binds each value to its matching parameter name inside the function's own local scope. The return statement is how a result escapes back to whoever called the function. Without return, Python hands back None — nothing useful. The calling code can then store or use that result: result = area(5, 3) gives result the value 15. In some languages — Pascal, Ada, Visual Basic — the word procedure means a callable that intentionally has no return value (it acts purely through side effects like printing). Python makes no such keyword distinction; every callable is a function and every function returns something, even if that something is None by default. Knowing both conventions helps you read code across languages. The deeper payoff is abstraction: once area works, anyone can call it by name without ever re-reading the multiplication inside. The messy details are hidden behind a clean interface, which is exactly how large programs stay manageable. Stuck? Name the one job your function should do, then ask: what input does it need (parameters) and what result should it send back (return value)?