I love Python, but it's a minefield of a language. Here's some things I do to have confidence in the code I write.
Always log exceptions
Exceptions are the standard path for error reporting in Python, however, I often stumble across code
that doesn't make use of logger.exception() when handling exceptions. The result is errors which
get eaten by the exception handling.
Use a better logger
The Python standard logger is not my favorite. It's the Denny's of loggers in that it's got
something for everyone but nothing I want in particular unless I'm drunk at 1 am. I prefer something
like structlog, but anything that doesn't blow up when you pass it a string that's actually None
will suffice.
Use typehinting
Typehinting will save your users from fighting runtime errors. It's not a perfect system, but defensive programming isn't about absolute certainty - it's about cutting down on the mole hills that you can trip on.
Check for None
In a language like Python if there's a chance that it can be None then there's a non-zero chance
it'll be None for one of your users at some point in the future. It's kind of annoying, but I tend
to wrap a none-check around returns from certain libraries that converts them to an exception.