How to Add a String to All Keys in a Python Dictionary Without Creating a New Dictionary

Discover how to effectively modify dictionary keys in Python by appending strings with this simple guide. Learn the best practices to avoid common errors and ensure smooth code execution. --- This video is based on the question https://stackoverflow.com/q/67005248/ asked by the user 'Benn' ( https://stackoverflow.com/u/13170612/ ) and on the answer https://stackoverflow.com/a/67005333/ provided by the user 'Mad Physicist' ( https://stackoverflow.com/u/2988730/ ) 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: Python add string to dictionary keys 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. --- How to Add a String to All Keys in a Python Dictionary Without Creating a New Dictionary If you're working with dictionaries in Python, you might find yourself in a situation where you want to prepend or append a string to all keys in the dictionary. Now, you may think that the easiest approach would be to just iterate over the keys and change them directly. However, this is where things can get tricky due to Python's handling of dictionary keys. Recently, a user encountered an issue where they received a RuntimeError when attempting to modify dictionary keys during iteration. Let's delve into the problem and explore the solution. The Problem Here's a look at the original question posed: The user had a dictionary structured as follows: [[See Video to Reveal this Text or Code Snippet]] They wanted to prepend the string "Test " to each key in the dictionary without creating a new dictionary. However, when they tried the following code: [[See Video to Reveal this Text or Code Snippet]] They received this error: [[See Video to Reveal this Text or Code Snippet]] The Solution To avoid this error, you need a method that allows you to change the keys without modifying the dictionary while iterating over it. Here’s a step-by-step breakdown of how you can achieve this: Step 1: Use a Separate List for Iteration By creating a list of the keys to iterate over, you can safely modify the dictionary. Here's how: [[See Video to Reveal this Text or Code Snippet]] In this code: The expression list(result) generates a list of the original keys in the dictionary. This allows you to iterate over it without affecting the original dictionary structure. Step 2: Prevent Key Overwriting When changing keys, you might encounter a scenario where new keys share names with the old keys. To prevent overwriting, you can sort the keys to avoid conflicts. This can be done as follows: [[See Video to Reveal this Text or Code Snippet]] Example Complete Code Combining the above steps, here’s the complete code: [[See Video to Reveal this Text or Code Snippet]] Result After executing the code, you will receive the following output: [[See Video to Reveal this Text or Code Snippet]] Now you have successfully modified your dictionary keys by prepending the string without generating a new dictionary! Conclusion By appending or prepending strings to dictionary keys using a separate list for iteration, you can avoid the common pitfalls associated with modifying dictionaries in Python. This method ensures your code runs smoothly and efficiently while achieving the desired results. If you encounter similar situations in your Python programming journey, remember this approach to handle dictionary keys effectively.