Learning Python: Day 16

can use a for loop and an if statement to change the color of the aliens

# Make an empty list for storing aliens.

aliens = []

# Make 30 green aliens.

for alien_number in range (30):

….new_alien = {‘color’: ‘green’, ‘points’: 5, ‘speed’: ‘slow’}

….aliens.append(new_alien)

for alien in aliens[:3]:

….if alien[‘color’] == ‘green’:

……..alien[‘color’] = ‘yellow’

……..alien[‘speed’] = ‘medium’

……..alien[‘points’] = 10

# Show the first 5 aliens.

for alien in aliens[:5]:

….print(alien)

print(“…”)

slice only includes the first three aliens we want to modify
can write an if statement to make sure we’re only modifying green aliens
if gree, we change the color to yellow, the speed to medium, and the point value to 10

{‘color’: ‘yellow’, ‘points’: 10, ‘speed’: ‘medium’}

{‘color’: ‘green’, ‘points’: 5, ‘speed’: ‘slow’}

…

can expand loop by adding an elif block that turns the yellow aliens into red, fast-moving ones worth 15 points each

for alien in aliens[0:3]:

….if alien[‘color’] == ‘green’:

……..alien[‘color’] = ‘yellow’

……..alien[‘speed’] = ‘medium’

……..alien[‘points’] = 10

….elif alien[‘color’] == ‘yellow’:

……..alien[‘color’] = ‘red’

……..alien[‘speed’] = ‘fast’

……..alien[‘points’] = 15

common to store a number of dictionaries in a list when each dictionary contains many kinds of information about one object
for example, creating a dictionary for each user on a site and storing individual dictionaries in a list called users
due to all dictionaries in the list having identical structure, you can loop through the list and work with each dictionary object in the same way

A list in a dictionary

sometimes it’s more useful to put a list inside a dictionary rather than putting a dictionary inside a list
for example, consider how you might describe a pizza someone is ordering
if you were to only use a list, all you could store is a list of pizza toppings
with a dictionary, a list of toppings can be one aspect of the pizza
the following example stores two kinds of information for each pizza: a type of crust and a list of toppings
list of toppings is a value associated with the key toppings
to use the items in the list, we give the name of the dictionary and the key toppings, as we would any value in a dictionary
instead of returning a single value, we get a list of toppings

pizza.py

# Store information about a pizza being ordered.

pizza = {

….’curst’: ‘thick’,

….’toppings’: [‘mushrooms’, ‘extra cheese’],

….}

# Summarize the order.

print(f”You ordered a {pizza[‘curst’]}-crust pizza “

….”with the following toppings:”)

for topping in pizza[‘toppings’]:

….print(f”\t{topping}”)

we begin with a dictionary that holds information about a pizza that has been ordered
one key in the dictionary is crust and the value is the string thick
next key toppings has a list as its value that stores all requested toppings
we summarize the order before building the pizza
when you need to break up a long line in a print() call, choose a spot and end the line with a quotation mark
indent the next line, add an opening quotation mark, and continue the string
Python will automatically combine all of the strings it finds inside the parentheses
use a for loop to print the toppings
use key toppings to access the list of toppings

You ordered a thick-crust pizza with the following toppings:

….mushrooms

….extra cheese

you can nest a list inside a dictionary anytime you want more than one value to be associated with a single key in a dictionary
in the earlier example of favorite programming languages, if we were to store each person’s responses in a list, people could choose more than one language
when we loop through the dictionary, the value associated with each person would be a list of languages rather than a single language
inside the dictionary’s for loop we use another for loop to run through the list of languages associated with each person

favorite_languages.py

….favorite_languages = {

….’jen’: [‘python’, ‘rust’],

….’sarah’: [‘c’],

….’edward’: [‘rust’, ‘go’],

….’phil’: [‘python’, ‘haskell’],

….}

for name, languages in favorite_languages.items():

….print(f”\n{name.title()]’s favorite languages are:”)

for language in languages:

….print(f”\t{language.title()}”)

value associated with each name in favorite_languages is now a list
we use variable name languages to hold each value from he dictionary, because each value will be a list
inside the main dictionary lop, we use another for loop to run through each person’s list of favorite languages

Jen’s favorite languages are:

….Python

….Rust

Sarah’s favorite languages are:

….C

Edward’s favorite languages are:

….Rust

….Go

Phil’s favorite languages are:

….Python

….Haskell

to refine this program even further, you could include an if statement at the beginning of the dictionary’s for loop to see whether each person has more than one favorite language by examining the value of len*(languages)
if a person has more than one favorite, the output would stay the same
if the person has only one favorite language, you could change the wording to reflect that
for example, “Sarah’s favorite language is C.”
you shouldn’t nest lists and dictionaries too deeply

A dictionary in a dictionary

you can nest a dictionary inside another dictionary, but your code can get too complicated
for example, users on a site, each with a unique username, you can use the usernames as the keys in a dictionary
you can then store information about each user by using a dictionary as the value associated with their username

many_users.py

user = {

….’aeinstein’: {

….’first’: ‘albert’,

….’last’: ‘einstein’,

….’location’: ‘princeton’.

….},

….’mcurie’: {

….’first’: ‘marie’,

….’last’: ‘curie’,

….’location’: ‘paris’.

….},

}

for username, user_info in users.items():

….print(f”\nUsername: {username}”)

….full_name = f”{user_info[‘first’]} {user_info[‘last’]}”

….location = user_info[‘location’]

….print(f”\tFull name: {full_name.title()}”)

….print(f”\tLocation: {location.title()}”)

first defined a dictionary, called users, with two keys: one each for the usernames
the value associated with each key is a dictionary that includes each user’s first name, last name, and location
we loop through the users dictionary, Python assigns each key to the variable username, and the dictionary associated with each username is assigned to the variable user_info
once inside the main dictionary loop, we print the username
then we start accessing the inner dictionary
the variable user_info, has three keys: first, last, and location
use each key to generate a neatly formatted full name and location and print he summary of what we know

Username: aeinstein

….Full name: Albert Einstein

….Location: Princeton

Username: mcurie

….Full name: Marie Curie

….Location: Paris

Summary

learned how to define. dictionary and how to work with info inside
learned how to access and modify individual elements in a dictionary and how to loop through all of the information in a dictionary
learned to loop through a dictionary’s key-value pairs, keys, and values
learned how to nest multiple dictionaries in a list, nest lists in a dictionary, and nest a dictionary inside a dictionary

Learning Python: Day 16

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