Hi @wuaham, Builder will regenerate the Python file it creates, each time you run the experiment from builder. If you have custom code, your best option is to use a code component, where you can insert snippets of code throughout your experiment. Builder will write this code from the code component to your Python file. This is the best solution. If for any reason, you do not want to do this, then you can edit your Builder-generated Python script, and change the filename, so that Builder does not overwrite it. However, at this point, the file will no longer be updated if you change your experiment in Builder. We recommend the use of code components, because it offers the same flexibility, allowing you too add custom code whilst keeping your script up to date with your builder file.