Reusable code

Ideas to remember

1. 01A function is a small, named piece of a program that solves one specific sub-problem, and you reuse it by calling its name.
2. 02Defining a function does not run it; the code inside runs only when you call it.
3. 03A variable created inside a function is local to it and is gone when the function finishes; a value travels out through return.
4. 04Modular thinking is build small, then combine: draw_house only calls draw_square and draw_triangle and repeats no drawing code.
5. 05import brings in a ready-made collection of functions, and a module is nothing more than a Python file.
6. 06A list keeps many values in one ordered container, and Python counts positions from 0, not from 1.

Words

def add(a, b):

Defines a function named add with two arguments; return a + b hands the sum back to whoever called it.

draw_shape(length, num_sides)

Draws a regular polygon; the turtle turns 360 / num_sides degrees at each corner.

import turtle

Loads all the drawing functions, so turtle.forward(100) shows exactly where forward comes from.

list[0]

The first item; the last item of a five-item list is list[4], not list[5].

append, insert, remove, pop

append adds to the end, insert puts an item at a chosen index, remove drops an item by value, pop removes the last item and hands it back.

len, [start:stop]

len tells you how many items a list holds; slicing pulls out a run of items, and the stop index is not included.