Скачать или смотреть Create a List of Dictionaries from a Python List in an Easy Way

Learn how to efficiently create a list of dictionaries in Python by iterating over an existing list. We provide a clear explanation and code examples to simplify the process.
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Creating a List of Dictionaries from a List in Python

Have you ever wondered how to transform a simple list into a more structured format in Python? Specifically, creating a list of dictionaries based on an existing list can seem complex at first, especially when you need to query a database to populate the dictionary values. In this guide, we will answer the question: how to create a list of dictionaries after iterating over a list?

Understanding the Problem

Let's take a look at a sample list of programs you have:

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When you iterate over this list, you perform a database query that retrieves the number of users for each program for the years 2020 and 2021. The goal is to compile this information into a list of dictionaries where each dictionary corresponds to a program and includes:

PROGRAM_NAME: The name of the program

Number of users in 2020: Retrieved value from the database for the year 2020

Number of users in 2021: Retrieved value from the database for the year 2021

You aim for a structure like this:

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The Solution

Creating this list of dictionaries can be achieved in a few simple steps. Here’s how to do it efficiently in Python:

Step 1: Initialize an Empty List

First, you will need to create an empty list where you will store your dictionaries.

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Step 2: Iterate Over the List of Programs

Next, you'll loop through the programs list. For every program, you will execute your database query to get the number of users.

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Step 3: Create and Populate the Dictionary

Within the loop, create an empty dictionary and fill it with the desired keys and values.

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Step 4: Append the Dictionary to the List

To ensure that each dictionary is added as a separate entity in your list (rather than a reference), use the .copy() method when appending.

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Complete Code Example

Here is how the full code might look:

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One-Liner Version (Optional)

As an alternative, you can streamline this process using a one-liner to create your dictionary:

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Conclusion

Creating a list of dictionaries in Python from an existing list may seem challenging at first, but by breaking it down into manageable steps, you can easily achieve your goal. Make sure to understand the importance of using copy() when appending dictionaries to your list to avoid potential reference issues. With this structured approach, you can now efficiently organize your program data and enhance your applications!

Happy coding!