Beginner Python Cheat Sheet - Dictionaries (Python Crash Course)

Question 1

1. How do you access a dictionary value?

2. What’s another way to access a dictionary value?

Answer 1

E.g.
alien_0 = {‘color’: ‘green’, ‘points’: 5}

1. print(alien_0[‘color’])
   print(alien_0[‘points’])
2. alien_color = alien_0.get(‘color’)
   alien_points = alien_0.get(‘points’, 0)

The 0 in this case is what will return if the key does not exist

Get returns none instead of an error if the dictionary doesn’t exist

Question 2

How do you add a key-value pair in a dictionary?

Answer 2

E.g.

alien_0[‘x’] = 0

Question 3

How do you remove a key value pair?

Answer 3

E.g.

del alien_0[‘points’]

Question 4

1. How do you loop through all of the keys and values?
2. How do you loop through just the keys?
3. How do you loop through just the values?

Answer 4

1. for name, language in fav_languages.items():
   print(name + “: “ + language)
2. for name in fav_languages.keys():
   print(name)
3. for name in sorted(fav_languages.values()):
   print(name + “: “ + language)

Question 5

What’s an example of iterating through a nested list of dictionaries?

Answer 5

E.g.
# Start with an empty list.
users = []
# Make a new user, and add them to the list.
new_user = {
 'last': 'fermi',
 'first': 'enrico',
 'username': 'efermi',
 }
users.append(new_user)
# Make another new user, and add them as well.
new_user = {
 'last': 'curie',
 'first': 'marie',
 'username': 'mcurie',
 }
users.append(new_user)
# Show all information about each user.
for user_dict in users:
    for k, v in user_dict.items():
        print(k + ": " + v)
    print("\n")

Question 6

What’s an example of iterating through lists within a dictionary?

Answer 6

E.g.

# Store multiple languages for each person.
fav_languages = {
 'jen': ['python', 'ruby'],
 'sarah': ['c'],
 'edward': ['ruby', 'go'],
 'phil': ['python', 'haskell'],
}
# Show all responses for each person.
for name, langs in fav_languages.items():
 print(name + ": ")
 for lang in langs:
 print("- " + lang)

Question 7

How do you preserve the order in a dictionary?

Answer 7

Use the OrderedDict() function

Question 8

Give an example of using the dict() function

Answer 8

> > > # creating empty dictionarydict()
{}

> > > dict(m=8, n=9)
{‘m’: 8, ‘n’: 9}

Through a kwargs type setup (keyword value pairs)