A program that reads like a list of steps is a program made of functions. Each function is one step, and the main code names the steps in order.
About 2 min of reading
Before this new lesson, one small question about the lesson you just finished. Recall it, do not look it up.
Split one block into three functions.
Write three one-step functions.
Before you run it, say out loud what it will print. Then open the answer.
Run them in order.
Before you run it, say out loud what it will print. Then open the answer.
Put the plan in a main function and call it.
Before you run it, say out loud what it will print. Then open the answer.
Call one piece alone with your own values.
Before you run it, say out loud what it will print. Then open the answer.
Before you write anything, put these lines back in the right order. Click a line to move it up one step. This support step is easier than writing code from scratch, and it is here to make the last example stick.
Read the first example one line at a time. A line that prints shows what appears on screen; the rest set things up quietly.
Start by naming the steps of the whole job. Each name becomes a function, and each function is split the same way until the steps are one or two lines.
A small function has a name, an input, and an output. That shape can be read, tested, moved, and deleted on its own. A long block cannot.
def read_data():
return [1, 2, 3]
def work(items):
return sum(items)
def show(total):
print(total)
show(work(read_data()))Three functions, three steps. The last line reads as do this, then this, then this.
def celsius(f):
return (f - 32) * 5 / 9
def report(t):
return str(round(t)) + "C"
print(report(celsius(68)))Converting and formatting are different ideas. Keeping them apart means each one can be checked on its own.
def main():
items = read_data()
total = work(items)
show(total)
main()main holds only the plan. Every detail lives one level down, which is what makes the plan readable at a glance.
def work(items):
return sum(items)
print(work([2, 2]))Because work takes its input and returns its output, you can call it alone with values you chose. Testing a piece needs no setup.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.