How to Create a Dictionary with Multiple Values in Python

Learn how to efficiently create a dictionary from two lists in Python, pairing countries with their cities using simple step-by-step methods.
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How to Create a Dictionary with Multiple Values in Python: A Comprehensive Guide

Creating a dictionary with multiple values from two lists can often be a challenge for new Python programmers. Imagine having two lists: one containing countries with possible duplicates and another featuring unique cities that correspond to these countries. In this guide, we'll explore how to transform these two lists into a well-structured dictionary where each country is associated with its respective cities.

The Problem

Let's say you have the following two lists:

List of Countries:

[[See Video to Reveal this Text or Code Snippet]]

List of Cities:

[[See Video to Reveal this Text or Code Snippet]]

Your objective is to create a dictionary that maps each country to a list of its corresponding cities. The expected output should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Initial Attempt

You might have tried a nested loop solution like this:

[[See Video to Reveal this Text or Code Snippet]]

However, this approach resulted in only being able to pull out a single record:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

Step 1: Using zip()

The zip() function allows you to pair elements from both lists together. This way, you can iterate over both lists simultaneously.

Step 2: Initializing the Dictionary

You can start with an empty dictionary to store the results.

Step 3: Populating the Dictionary

For each pair of country and city, utilize setdefault() to create an empty list for the country if it doesn’t exist, and then append the city to the vector for that country.

Here’s the complete code solution:

[[See Video to Reveal this Text or Code Snippet]]

As an alternative, you can utilize defaultdict from the collections module, which simplifies the initialization of lists for missing keys. Here’s how to implement it:

[[See Video to Reveal this Text or Code Snippet]]

Summary

Understanding zip(): Efficiently pair elements from two lists.

Utilizing setdefault(): Create lists as needed for missing keys in a dictionary.

Using defaultdict: Simplify initialization of lists for multiple values in a dictionary.

With this guide, you should now be able to easily create a dictionary mapping countries to their cities in Python. Experimenting with these approaches can help reinforce your understanding of dictionary operations.

If you have any questions or need further assistance, feel free to reach out. Happy coding!