How to Append a New Key-Value Pair to a Dictionary in a List Based on Existing Key Matches in Python

Описание: Learn how to modify dictionaries within a list in Python by appending new key-value pairs when existing key-value pairs match, utilizing efficient loops and updates.
---
This video is based on the question https://stackoverflow.com/q/69946185/ asked by the user 'thinkpythonxoxo' ( https://stackoverflow.com/u/17397122/ ) and on the answer https://stackoverflow.com/a/69946355/ provided by the user 'Tom' ( https://stackoverflow.com/u/13386979/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: List of Dictionaries Python: Append a new key, value pair to dictionary if existing key, value pair matches

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Introduction to Updating Dictionaries in Python Lists

In the world of Python programming, managing collections of data often leads us to work with lists of dictionaries. A common task you might encounter is needing to append new information to these dictionaries based on certain conditions. In particular, let's consider a situation where you want to add a new key-value pair to dictionaries in a list if a specific existing key and its value match certain criteria. This task can arise in a variety of applications, such as data processing or configuration management.

In this guide, we'll explore how to efficiently update dictionaries in a list when a matching key-value pair is found. We'll walk through a practical example to illustrate the solution clearly, making use of simple looping and dictionary manipulation techniques.

The Problem Statement

Suppose we have the following list of dictionaries representing records:

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

And we have another list that contains new information to be appended to matching records:

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

Objective

Our goal is to iterate through original_list and update each dictionary with the corresponding new_record from to_append when there is a match in the value of record1. If there is no match, we leave the original dictionary unchanged.

Solution Approach

To achieve this, we will use a nested loop to check for matching record1 values in both lists. If a match is found, we will update the corresponding dictionary in original_list with the contents of to_append. Here's how to do that step-by-step:

Step-by-Step Implementation

Initialize the Lists: Start with the original list of dictionaries and the new items that need to be appended.

Nested Loop for Comparison: Use a loop to go through each dictionary in the original list, and a nested loop to compare it against each dictionary in to_append.

Check for Matches: Within the inner loop, check if the record1 values from both dictionaries are equal.

Update the Dictionary: If a match is found, use the update() method to append the new key-value pair.

Here's the implementation code in Python:

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

Expected Output

After executing the above code, the original_list will be modified to include the new records where applicable:

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

Important Considerations

When implementing this solution, keep in mind the following:

Modification of the Original List: The approach modifies the original dictionaries directly rather than creating new ones.

Key Existence: If any dictionary lacks the key 'record1', you'll encounter a KeyError. It's important to ensure that every dictionary has this key, or handle cases where it might be absent.

Handling Duplicates: If there are multiple matches in to_append for a single dictionary in original_list, this may lead to overwriting earlier values in new_record.

Conclusion

By following the steps outlined above, you can effectively append new data to existing dictionaries in a list based on conditions you specify. This technique is versatile and can be adapted for various data manipulation tasks in Python. Happy coding!