PRbsas/introduction-to-functions-lab-data-science-intro-000

Functions lab

Introduction

As we know, we can use functions to name sequences of our code, thus making our code more expressive. We can also use functions to allow us to reuse our code. In this lab we will practice using functions for these purposes.

Objectives

• Practice declaring and returning values from functions
• Practice accessing variables that are outside of a function's scope, from inside of a function

Writing our first functions

Imagine we are working on our list of travel destinations -- which is really turning out to be a full time job. We have our list of travel_destinations which we assign below. Write a function called number_of_destinations that returns the number of destinations we have on our list.

travel_destinations = ['argentina', 'mexico', 'italy', 'finland', 'canada', 'croatia']
def number_of_destinations():
    pass

number_of_destinations() # 6

Now write another function called next_up that returns our first destination (the destination with the lowest index), in the travel_destinations list.

def next_up():
    pass

travel_destinations = ['argentina', 'mexico', 'italy']
next_up() # 'argentina'

travel_destinations = ['finland', 'canada', 'croatia']
next_up() # 'finland'

Ok, now write a function called favorite_destination that returns the string 'madagascar'.

travel_destinations = ['argentina', 'mexico', 'italy', 'finland', 'canada', 'croatia']
def favorite_destination():
    pass

favorite_destination() # 'madagascar'

Again, let's declare an array called travel_destinations. Change the function favorite_destination so that it continues to return the string 'madagascar', but also adds the string 'madagascar' to the end of the list of destinations.

travel_destinations = ['argentina', 'mexico', 'italy', 'finland', 'canada', 'croatia']
favorite_destination()
travel_destinations[-1] # 'madagascar'

Now let's write another function which iterates through the list of destinations and capitalizes the first letter of each word. It should return a list of capitalized destinations.

travel_destinations = ['argentina', 'mexico', 'italy', 'finland', 'canada', 'croatia']
def capitalize_countries():
    pass

capitalize_countries() # ['Argentina', 'Mexico', 'Italy', 'Finland', 'Canada', 'Croatia']

Great! Now if someone adds a country that is lowercased to our list of destinations, we can simply call our function again to capitalize each of the destinations in the list.

travel_destinations = ['argentina', 'mexico', 'italy', 'finland', 'canada', 'croatia']
capitalize_countries() # ['Argentina', 'Mexico', 'Italy', 'Finland', 'Canada', 'Croatia']
travel_destinations.append('japan')
capitalize_countries() # ['Argentina', 'Mexico', 'Italy', 'Finland', 'Canada', 'Croatia', 'Japan']

Summary

Great job! In this lab we were able to get practice both writing and returning values from functions. We also practiced accessing variables not local to the function but in the global scope.