In many languages each += on a string copies everything built so far into a new string. Build a report line by line and the copying grows with the square of its length.
The fix you can use today
Collect the parts in a list and join once: ''.join(parts) in Python.
Use StringBuilder in Java and C#, strings.Builder in Go, a buffer elsewhere.
Look for += on strings inside loops in code review.
GreenCode researchers list building strings in a loop among the worst energy wasters in code.
Tools that help
GreenCode Constitution skill (GreenCode researchers): open-source energy principles and a catalogue of 37 energy anti-patterns that an AI coding agent can follow to find and fix waste like this
green-languages (GreenCode researchers): a command-line tool that measures the energy of whole programs or marked sections of code, across languages
How GreenCode helps
GreenCode helps tackle this by refactoring flagged code one element at a time. It writes any missing tests and documentation first, and returns every change as a pull request for a person to approve. More on this.
