Dictionaries in Python

Intro

In my previous blog I went over 3 of the built in data sets in Python: lists, tuples, and sets. In this blog we will go over another built in Python data set, dictionaries.

What are Dictionaries?

Dictionaries are used to store value in a key:value pairs. Dictionaries are unordered, do not allow duplicates, and can be changed.

Create a Dictionary

To create a dictionary we use the follow syntax:

variable_name = {key:value}

# example
friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

Access a dictionary item

To access a dictionary item we use the following syntax:

friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

print(friend_ages["Adam"])  # 30

If you need to print the entire dictionary you just use print and the dictionary like this:

friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

print(friend_ages)  # {"Rolf": 24,"Adam": 30,"Anne": 27}

Change an Item in a Dictionary

To change an item in a dictionary we use a similar syntax as accessing an item:

friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

friend_ages["Rolf"] = 21

print(friend_ages["Rolf"]) # 21

Add an Item to a Dictionary

To add an item to a dictionary we use the following syntax:

friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

friend_ages["Danny"] = 38

print(friends_ages) # {"Rolf": 24,"Adam": 30,"Anne": 27,"Danny":38}

Delete an Item

To delete an item in a dictionary we use the pop() method:

friend_ages = {
    "Rolf": 24,
    "Adam": 30,
    "Anne": 27
}

friend_ages.pop("Adam")

print(friends_ages) # {"Rolf": 24,"Anne": 27}

Loop Through a Dictionary

Finally to loop through a dictionary we use a for loop:

student_attendance = {"Rolf": 96, "Bob": 80, "Anne": 100}

for student in student_attendance:
    print(student)  # Rolf, Bob, Anne

# print every key value pair

for student in student_attendance:
    print(f"{student}: {student_attendance[student]}")
# Rolf: 96
# Bob: 80
# Anne: 100