[$] Corner cases and exception types
Some unanticipated corner cases with Python's new "walrus"
operator—described in our Python 3.8
overview—have cropped up recently. The problematic uses of the operator
will be turned into errors before the final release, but just what
exception should be raised came into question. It seems that the exception
specified in the PEP for the operator may not really be the best choice, as a
recent discussion hashed out.