Function Composition in Python — ELI5

Think about getting dressed in the morning.

First you put on a shirt. Then a jacket over it. The shirt is one step, the jacket is another, but together they make an outfit. You don’t think of them as separate actions anymore — it’s just “getting dressed.”

Function composition in Python is exactly that.

You take two small functions and combine them into one bigger function. The first function does its job, then its result goes straight into the second function. Now you have a single function that does both jobs at once.

Why is this cool?

• You can build complicated things from tiny, simple pieces.
• Each piece is easy to test on its own.
• You can mix and match pieces to create new combinations without rewriting anything.

It’s like having a box of crayons. Red and blue are simple by themselves. But when you layer red over blue, you get purple — a brand new color from two pieces you already had.

In Python, you might have a function that doubles a number and another that adds one. Compose them, and you get a new function that doubles then adds one — all in a single step.

One Thing to Remember

Function composition is snapping two small functions together so the output of the first automatically becomes the input of the second — giving you one new, more powerful function.