Bug introduced in #832

[sglvladi]

In trying to fix one bug in #832, I inadvertently introduced another bug that somehow evaded all the tests.

This is caused by incorrect use of the walrus operator on line 244 of base.py, meaning that the variable excess always takes a Boolean value (i.e. 0 or 1), therefore leading to inappropriate execution of the while loop for each character in val, which in turn led to scripts hanging.