This is what I've done for a project. I have a few data structures that are bascially dictionaries with some methods that operate on the data. When I save them to disk, I write them out to .py files as code that when imported as a module will load the same data into such a data structure.
Is this reasonable? Are there any big disadvantages? The advantage I see is that when I want to operate with the saved data, I can quickly import the modules I need. Also, the modules can be used seperate from the rest of the application because you don't need a separate parser or loader functionality.
It's reasonable, and I do it all the time. Obviously it's not a format you use to exchange data, so it's not a good format for anything like a save file.
But for example, when I do migrations of websites to Plone, I often get data about the site (such as a list of which pages should be migrated, or a list of how old urls should be mapped to new ones, aor lists of tags). These you typically get in Word och Excel format. Also the data often needs massaging a bit, and I end up with what for all intents and purposes are a dictionaries mapping one URL to some other information.
Sure, I could save that as CVS, and parse it into a dictionary. But instead I typically save it as a Python file with a dictionary. Saves code.
So, yes, it's reasonable, no it's not a format you should use for any sort of save file. It however often used for data that straddles the border to configuration, like above.