Idea: conversions= could take Python functions

Right now you use conversions= like this:

db["example"].insert({
    "name": "The Bigfoot Discovery Museum"
}, conversions={"name": "upper(?)"})

How about if you could optionally provide a Python function (or a lambda) like this?

db["example"].insert({
    "name": "The Bigfoot Discovery Museum"
}, conversions={"name": lambda s: s.upper()})

This would work by creating a random name for that function, registering it (similar to #162), executing the SQL and then un-registering the custom function at the end.

Start with the existing conversions= handling in the Python database API and read issue #162 for the related custom-function registration approach. Done means conversions= accepts a Python function or lambda, executes the SQL using a registered function, and unregisters it afterward.