For example: I import a module of helper functions into my main script and test the script in RF. And then when I have to edit one of the helper functions, RF isn't "aware" of the changes. I usually quit and re-open RF and then it'll work fine.

My understanding is that .pyc files are created on import, at runtime, and I assume this is why RF doesn't see the changes in the imported module, but I don't see those files (or a __pycache__) folder in my dev folder. Are they stored somewhere in Application Support?

import module

import importlib
importlib.reload(module)

You will have to do this for each ‘file’ in your module.
Be careful with subclasses of NSObjects.

For development I would recommend to have a main.py that load the extension so you can run this directly in the scripting window.

good luck!

Another problem I'm having is that if I have 2 extensions with some helper functions in a utils directory, when I try to run the second one, I get a ModuleNotFoundError for something in the utils directory.

For example:

Extension1.roboFontExt
└── lib
    ├── extensionName.py
    └── utils
        ├── __init__.py
        └── helperFunctions.py

Extension2.roboFontExt
└── lib
    ├── anotherExtension.py
    └── utils
        ├── __init__.py
        └── calculations.py

When I have Extension1 installed and I try to run Extension2 from the scripting window, I'll get something like ModuleNotFoundError: No module named utils.calculations.

Should I treat each extension like a package and put an __init__.py in the lib folder of each extension?

Extension1.roboFontExt
└── lib
    ├── __init__.py
    ├── extensionName.py
    └── utils
        ├── __init__.py
        └── helperFunctions.py

Extension2.roboFontExt
└── lib
    ├── __init__.py
    ├── anotherExtension.py
    └── utils
        ├── __init__.py
        └── calculations.py

the recommendation is to use reverse domain names (without dots) to create unique names for extension modules:

• comJesentanadiExtensionNameUtils (Extension1)
• comJesentanadiAnotherExtensionUtils (Extension2)

see the note in Extension File Specification > lib