Chapter 6

Dictionaries

Def: A collection of key-value pairs. Each key is connect to a value, and you can use a key to access the value associated with that key.
A key can be:

• a number
• a string
• a list
• another dictionary
• any object created in python

A dictionary is wrapped in braces {} and a dynamic structure, thus you can add a new key-value pair at any time.

Dictionaries allow you to connect pieces of related information, can store a limitless amount of information, and model a variety of real-world objects.

Dict. alien example

alien_o = {"color": "green", "points":5}
print(alien_o["color"])
print(alien_o["points"])

Adding New Key-Value pairs

alien_o = {"color": "green", "points":5}
print(alien_o["color"])
print(alien_o["points"])

alien_o["x_position"] = 0
alien_o["y_position"] = 25

print(alien_o)

Modifying Values in Dictionary

alien_o = {"color": "green", "points":5}
print(alien_o["color"])
print(alien_o["points"])

alien_o["x_position"] = 0
alien_o["y_position"] = 25

alien_o["color"] = "blue"

print(alien_o)

Removing key-value pairs

del dict["name_of_key"]

alien_o = {"color": "green", "points":5}
print(alien_o["color"])
print(alien_o["points"])

alien_o["x_position"] = 0
alien_o["y_position"] = 25

alien_o["color"] = "blue"

del alien_o["points"]

print(alien_o)

Using get() to access Values

Why? What if a key-pair value does not exist in a dictionary

alien_o = {"color": "green", "points":5}
print(alien_o["color"])
print(alien_o["points"])

alien_o["x_position"] = 0
alien_o["y_position"] = 25

alien_o["color"] = "blue"

del alien_o["points"]

point_value = alien_o.get("points", "No point value assigned.")
print(alien_o)
print(point_value)

Looping through a dictionary

user = {
    "username" : "The_first",
    "first" : "Jarin",
    "last" : "Almanzar",
}

for key, value in user.items():
    print(f"key is {key}")
    print(f"value is {value}\n")

Example 2 Of looping

fav_lang = {
    "jarlin" : "python",
    "Cris" : "Java",
    "Dante" : "SQL",
    "Arvin" : "C",
}

for name, language in fav_lang.items():
    print(f"{name}'s favorite language is {language}")

Looping Through all key and values in Dictionary

key() returns the keys of a dict
values() returns the values of a dict values()

fav_lang = {
    "jarlin" : "python",
    "Cris" : "Java",
    "Dante" : "SQL",
    "Arvin" : "C",
}

# For keys
for name in fav_lang.keys():
    print(name.title())

# For values
for language in fav_lang.values():
    print(language.title())

List of dicts.

alien_0 = {"color": "green", "points":5}
alien_1 = {"color": "yellow", "points":10}
alien_2 = {"color": "red", "points":10}

aliens = [alien_0, alien_1, alien_2]

for alien in aliens:
    print(alien)

A List in a Dict

pizza = {
    "crust": "thick",
    "toppings" : ["mushrooms", "onions", "extra cheese"],
}

print(f"You ordered a {pizza['crust']}-crust pizza")

A dict in a Dict

users = {
    "scientist": {
    "first" : "albert",
    "last" : "einstein",
    "location" : "princeton",
    },

}

# scientist is the key for alberrt einstein
for username, user_info in users.items():
    print(f"\n Username: {username}")
    print(f"\n fullname: {user_info['first']} and {user_info['last']}")