sqla_uuid.py

from uuid import UUID as py_UUID
from sqlalchemy.dialects.postgresql import BYTEA as pg_BYTEA
from sqlalchemy.dialects.oracle import RAW as ora_RAW
from sqlalchemy.types import TypeDecorator, BINARY

class sqla_type_UUID(TypeDecorator):

    impl = BINARY

    def __init__(self):
        self.impl.length = 16
        super(sqla_type_UUID, self).__init__(length=self.impl.length)

    def load_dialect_impl(self, dialect):
        if dialect.name == 'postgresql':
            return dialect.type_descriptor(pg_BYTEA(self.impl.length))
        elif dialect.name == 'oracle':
            return dialect.type_descriptor(ora_RAW(self.impl.length))

    def process_bind_param(self, value, dialect=None):
        # PY None => SQL null
        if not value:
            return None

        try:
            # passed a UUID object
            return value.bytes
        except AttributeError:
            # maybe I submitted a string of hex characters
            try:
                return py_UUID(value).bytes
            except ValueError:
                raise ValueError(
                    'value {} is not a valid representation of a UUID object'.format(value)
                ) from None
                
    def process_result_value(self, value, dialect=None):
        if value:
            # SQL binary => PY UUID
            return py_UUID(bytes=value)
        
        # SQL null => None
        return None
        

sqla_uuid_example.py

import uuid
from sqlalchemy import Column, String, Integer, DateTime, Text
from sqlalchemy.ext.declarative import declarative_base

from sqla_uuid import sqla_type_UUID

Base = declarative_base()

class ModelUUID(Base):
    __tablename__ = "mytable"
    
    uuid = Column(sqla_type_UUID, primary_key=True)
    short_text = Column(String(40))
    long_text = Column(Text)
    anint = Column(Integer)
    ts = Column(DateTime)
    
    # default on object create, pre-insert
    def __init__(self, *args, **kwargs):
        if 'uuid' not in kwargs:
            self.uuid = uuid.uuid4()
            
        super().__init__(*args, **kwargs)