TypeError is the standard Python error raised in this case:
$ python -c "(lambda a: None)(b=10)"
TypeError: <lambda>() got an unexpected keyword argument 'b'
We only used to raise InterfaceError when connect was used without
any parameter at all, so it's hard to think a program depending on
that design. Furthermore the function has always raised (and still
does) OperationalError too, if the bad argument is detected by the
libpq, and that cannot be changed because we can't tell the
difference from a normal connection error.