Using BBEdit With Python
I edit Python using BBEdit. BBEdit has a good Mac GUI and is full-feaured including being able to view invisible tabs and spaces which can be important when working with Python text files to keep the indentation consistent.
BBEdit also has a feature called "Zap Gremlins" that you can use to eliminate bad characters from your source code.
It also has a feature to be able to compare source files and even whole directories so that you can see the differences between versions.
And BBEdit allows you to run source code, including Python, from BBEdit without leaving it.
BBEdit doesn't have a command line. But if you really need to work interactively on occasion, you can go to Terminal and type in "python".
If you don't want to use BBEdit, there is a version of IDLE that runs on Mac OS X that has both an editor and a window with an interactive mode. I don't like IDLE because when I first tried it, I chose "Preferenes" from the Apple menu and it crashed. So, I lost my confidence in it.
You can google for "BBEdit Download" or "Python Mac IDLE Download" and find these products.
If you want something like BBEdit, nearly as good, but free. There is TextWrangler. You can find that by googling for "Text Wrangler Download".