memory usage for uuid.UUID seems larger than it has to be. it seems that using __slots__ will save around ~100 bytes per instance, which is very significant, e.g. when dealing with large sets of uuids (which are often used as "primary keys" into external data stores).

uuid.UUID has a __setattr__ that prevents any extra attributes to be
set:

    def __setattr__(self, name, value):
        raise TypeError('UUID objects are immutable')

...so it seems to me not having __dict__ should not cause any problems?


before (RES column):

>>> import uuid
>>> y = {uuid.uuid4() for _ in range(1000000)}

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
23020 wbolster   20   0  315M  253M  7256 S  0.0  1.6  0:04.98 python

with slots:

>>> import uuid
>>> y = {uuid.uuid4() for _ in range(1000000)}

  PID USER      PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
21722 wbolster   20   0  206M  145M  7348 S  0.0  0.9  0:05.03 python

i will open a pr on github shortly.