Functions and Scope

Functions and Modules — cheat sheet

Put repeated work in named functions, then use built-in tools and modules to keep code organized.

Define and return

def greet(name):
    print(f"Hello, {name}!")

Define reusable code with def and an indented body.

def add(left, right):
    return left + right

return sends a result back to the caller.

result = add(3, 4)

Call a function with arguments in parentheses.

def split_name(full_name):
    return full_name.split()

A function can return multiple values as a tuple.

def introduce(name, age):
    print(name, age)

Parameters receive values passed into a function.

introduce(age=12, name="Mina")

Keyword arguments name the parameter they fill.

def welcome(name, greeting="Hello"):
    print(greeting, name)

A default makes an argument optional.

def show_order(item, *extras, **details):
    print(item)

*extras and **details collect extra arguments.

message = "outside"
def show():
    print(message)

A function can read a global value.

def paint(color):
    print(color)

A parameter is local and can shadow a global name.

score = 0
def add_point():
    global score
    score += 1

global allows a function to reassign a global name.

def factorial(number):
    if number == 0:
        return 1
    return number * factorial(number - 1)

Recursive functions need a base case that stops calls.

words = ["pear", "fig"]
ordered = sorted(words, key=lambda word: len(word))

Use a lambda as a short sorting rule.

squares = list(map(lambda number: number * number, [1, 2, 3]))

map transforms every item with a function.

evens = list(filter(lambda number: number % 2 == 0, [1, 2, 3]))

filter keeps items whose test is true.

print(sum([2, 3]), min([2, 3]), max([2, 3]))

Built-ins solve common calculations quickly.

import math
print(math.sqrt(81))

Import a module, then use its names with a dot.

from math import ceil as round_up
print(round_up(4.2))

Import one name and optionally give it an alias.

import random
random.seed(0)
print(random.randint(1, 10))

A fixed seed makes a learning example repeatable.

if __name__ == "__main__":
    print("Starting")

This block runs when the file runs directly.