unnest_example.py

import sqlalchemy as sa
from sqlalchemy.dialects.postgresql import UUID, array

rec_order = sa.select(
         # using the 'WITH ORDINALITY' suffix adds a column named 'ordinality'
         # the first row (from the first array value) has ordinality 1, the second has 2, and so on
         # this is useful for sorting things by the array value; simply join on the array value
         # and order by ordinality
        [sa.column('ordinality', sa.Integer),
         # The actual column generated by unnest is named 'unnest' by default,
         # so I use a lightweight column construct to specify the name and type
         # and then apply a label to it
         sa.column('unnest', UUID).label('rec_uuid')],
        from_obj=sa.func.unnest(array(rec_uuids)))\
    .suffix_with('WITH ORDINALITY')\
    .alias('rec_order')

With this construct, I can now use rec_order.c.ordinality and rec_order.c.rec_uuid in my queries.