... and we have not that bad mapping type after all - lookup time is ~ the
same as in one-attr instance. My namedtuple implementation on the other
hand degrades awfully.

So, need to rework it. First observation is that named tuple fields are
accessed as attributes, so all names are interned at the program start.
Then, really should store field array as qstr[], and do quick 32/64 bit
scan thru it.