Change assertions to exception-raising conditionals

[atteggiani]

Overview

As reported by @penguian in this comment, there are assertions in the production code, which is not recommended.

Solution

Replacing assertions with conditionals that raise an error.
Something like:

- assert condition
+ if not condition:
+     raise Exception("...") # Choose the most appropriate Python Exception

For example:

- assert myvar > MINIMUM
+ if myvar <= MINIMUM:
+     raise ValueError(f"'myvar' must be greater than {MINIMUM}. It is {myvar}.")