text2num should raise ValueError instead of AssertionError

[millerdev]

From the docs

>>> text2num('mille mille deux cents')
AssertionError

First, an error message would be helpful to know what went wrong.

Second, the use of AssertionError here is a bad choice. An assertion error should only be raised if the program is internally inconsistent (has a bug). It should not be possible to cause an assertion error by supplying bad input (unless the program is internally inconsistent, and therefore is indicating it has a bug).

I think ValueError would be a better choice in this case since the user supplied a bad value. This is the same as passing a bad value to the built in int function:

>>> int("not a number")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'not a number'

text2num can't do anything about bad values passed to it other than raise an error indicating that it got a bad value.