Nested Dictionaries

1️⃣ What is a nested dictionary?

A nested dictionary is a dictionary that contains other dictionaries as its values. This allows for the organization of data in a hierarchical structure, where each key can map to another dictionary, enabling complex data representations. For example, consider the following nested dictionary:

# Example of a nested dictionary
person = {
    "name": "Alice",
    "age": 30,
    "address": {
        "street": "123 Main St",
        "city": "Somecity",
        "state": "Somestate",
        "country": "Somecountry"
    },
}

In this example, the person dictionary contains the keys name, age, and address. The value for the address key is another dictionary that contains keys street, city, state, and country. This structure allows for easy access to nested data.

2️⃣ How to access values in a nested dictionary?

To access values in a nested dictionary, you can use multiple keys in sequence, i.e. dict[“outer_key”][“inner_key”]. For example, to access the city value from the address dictionary in the person example above, you would do:

Accessing a value in a nested dictionary

person = { "name": "Alice", "age": 30, "address": { "street": "123 Main St", "city": "Somecity", "state": "Somestate", "country": "Somecountry" }, } # To access values in a nested dictionary, you can use multiple keys in sequence. # To access the "city" value from the "address" dictionary in the "person" example above, you would use: city = person["address"]["city"] print(city) # Output: Somecity

3️⃣ How to loop through the outer items of a nested dictionary?

To loop through the outer items (key-value pairs) of a nested dictionary, you can use a for loop with the .items() method. This method returns a list of a dictionary’s key-value tuple pairs. For example, to loop through the outer items of the person dictionary, you would do:

Looping through the outer items of a nested dictionary

person = { "name": "Alice", "age": 30, "address": { "street": "123 Main St", "city": "Somecity", "state": "Somestate", "country": "Somecountry" }, } # To loop through the outer items (key-value pairs) of a nested dictionary, # you can use a for loop with the .items() method. # This method returns a list of a dictionary’s key-value tuple pairs. # To loop through the outer items of the "person" dictionary, you would do: for outer_key, outer_value in person.items(): # This will print each key and its corresponding value in the person dictionary, # including the nested dictionary under the "address" key. print(f"{outer_key}: {outer_value}")

4️⃣ How to loop through the inner items of a nested dictionary?

To loop through the inner items of a nested dictionary, you can access the inner dictionary using its key and then use a for loop with the .items() method on that inner dictionary. For example, to loop through the inner items of the address dictionary in the person example, you would do:

Looping through the inner items of a nested dictionary

person = { "name": "Alice", "age": 30, "address": { "street": "123 Main St", "city": "Somecity", "state": "Somestate", "country": "Somecountry" }, } # To loop through the inner items of a nested dictionary, # you can access the inner dictionary using its key and then use a for loop with the .items() method on that inner dictionary. # To loop through the inner items of the "address" dictionary in the "person" example, you would do: for inner_key, inner_value in person["address"].items(): # This will print each key and its corresponding value in the "address" dictionary, # allowing you to access all the inner items. print(f"{inner_key}: {inner_value}")

5️⃣ How to add a new key-value pair to a nested dictionary?

To add a new key-value pair to a nested dictionary, you can specify the outer key and then assign a new key-value pair to the inner dictionary. For example, to add a new key zip_code to the address dictionary in the person example, you would do:

Adding a new key-value pair to a nested dictionary

person = { "name": "Alice", "age": 30, "address": { "street": "123 Main St", "city": "Somecity", "state": "Somestate", "country": "Somecountry" }, } # To add a new key-value pair to a nested dictionary, # you can specify the outer key and then assign a new key-value pair to the inner dictionary. # For example, to add a new key "zip_code" to the "address" dictionary in the "person" example, you would do: person["address"]["zip_code"] = "12345" print(person["address"]["zip_code"]) # Output: 12345

6️⃣ How to create an empty dictionary for a new category and add items later?

To create an empty dictionary for a new category in a nested dictionary, you can simply assign an empty dictionary to the outer key. Then, you can add items to this inner dictionary later. For example, if you want to create a new category hobbies in the person dictionary and add items later, you would do:

Creating an empty dictionary for a new category and adding items later

person = { "name": "Alice", "age": 30, "address": { "street": "123 Main St", "city": "Somecity", "state": "Somestate", "country": "Somecountry" }, } # To create an empty dictionary for a new category in a nested dictionary, # you can simply assign an empty dictionary to the outer key. # Then, you can add items to this inner dictionary later. person["hobbies"] = {} # Create an empty dictionary for the new category "hobbies". # Now you can add items to the "hobbies" category later. For example, you can add hobbies using a loop. hobby_list = [("reading", "Fiction"), ("exercise", "Running")] for hobby, detail in hobby_list: person["hobbies"][hobby] = detail # Add each hobby with its type to the "hobbies" dictionary print(person["hobbies"]) # Output: {'reading': 'Fiction', 'exercise': 'Running'}

What to do next

Click on the following link to finish the introduction: Introduction

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