The SDK contains a full complement of .py (uncompiled python files) for the stock game. As far as I know, there is no satisfactory way to open a compiled PYC. Even if you do manage to decompile it, a lot of the "readability" syntax will have been lost, and I'm pretty sure the comments explaining what does what will have been obliterated in the original compile.
You're better off with the source files provided with the SDK. Most modders provide the PY files to their work in the download, for your perusal.