Dictionaries

Introduction to Python for Developers

Jasmin Ludolf

Senior Data Science Content Developer

Ingredients list

ingredients = ["pasta", "tomatoes", "garlic", "basil", "olive oil", "salt"]


# Ingredient quantities (in grams)
quantities = [500, 400, 15, 20, 30, 5]

Dictionary

Dictionary = key-value pairs

Dictionary annotated with the word (key) and definition (value)

¹ https://unsplash.com/@sandym10

Why use dictionaries?

username
email
preferences

ip_address
location

Recipe scaler: link ingredients to quantities

User info

Computer network

¹ User image by Bilobaba Vladimir, Aviavlad; https://unsplash.com/@jjying

Creating a dictionary

# Creating a dictionary
recipe =

Creating a dictionary

# Creating a dictionary
recipe = {

Creating a dictionary

# Creating a dictionary
recipe = {"pasta"

Creating a dictionary

# Creating a dictionary
recipe = {"pasta":

Creating a dictionary

# Creating a dictionary
recipe = {"pasta": 500

Creating a dictionary

# Creating a dictionary
recipe = {"pasta": 500,

Creating a dictionary

# Creating a dictionary
recipe = {"pasta": 500,
          "tomatoes": 400,

Creating a dictionary

# Creating a dictionary
recipe = {"pasta": 500,
          "tomatoes": 400, 
          "garlic": 15,
          "basil": 20, 
          "olive oil": 30,
          "salt": 5

Creating a dictionary

# Creating a dictionary
recipe = {"pasta": 500,
          "tomatoes": 400, 
          "garlic": 15,
          "basil": 20, 
          "olive oil": 30,
          "salt": 5}

Accessing a value based on the key

Dictionaries are ordered
- Allows values to be accessed by subsetting on the key
How much pasta do we need?

# Find the ingredient's quantity
print(recipe["pasta"])

Accessing all values

# Get all values from a dictionary
print(recipe.values())

dict_values([500, 400, 15, 20, 30, 5])

Accessing all keys

# Retrieve all keys in a dictionary
print(recipe.keys())

dict_keys(['pasta', 'tomatoes', 'garlic', 'basil', 'olive oil', 'salt'])

Viewing an entire dictionary

# Print the dictionary
print(recipe)

{'pasta': 500, 'tomatoes': 400, 'garlic': 15, 'basil': 20, 'olive oil': 30,
'salt': 5}

# Get all items (key-value pairs)
print(recipe.items())

dict_items([('pasta', 500), ('tomatoes', 400), ('garlic', 15), ('basil', 20), 
('olive oil', 30), ('salt', 5)])

Adding a key-value pair

# Add a new key-value pair
recipe["parmesan"] = 50

print(recipe)

{'pasta': 500, 'tomatoes': 400, 'garlic': 15, 'basil': 20, 'olive oil': 30,
'salt': 5, 'parmesan': 50}

Updating a value

print(recipe)

{'pasta': 500, 'tomatoes': 400, 'garlic': 15, 'basil': 20, 'olive oil': 30,
'salt': 5, 'parmesan': 50}

# Updating a value associated with an existing key
recipe["pasta"] = 1000

print(recipe)

{'pasta': 1000, 'tomatoes': 400, 'garlic': 15, 'basil': 20, 'olive oil': 30,
'salt': 5, 'parmesan': 50}

Duplicate keys

# Creating a dictionary with a duplicate key
recipe = {"pasta": 500, "garlic": 5, 
          "garlic": 15, "basil": 20, 
          "olive oil": 30, "salt": 5}


# Print the duplicate key's value
print(recipe["garlic"])

Let's practice!

Introduction to Python for Developers