SQLAlchemy column type for storing Python enums

sqla_enum.py

from enum import Enum
from inspect import isclass
import re

from sqlalchemy.types import TypeDecorator, TypeEngine


__all__ = ['EnumType']


class EnumType(TypeDecorator):
    """Column type for storing Python :class:`Enum` types
    by converting them back-and-forth from & to a chosen SQL type.
    """
    def __init__(self, enum, impl):
        """Constructor.
        :type enum: Python :class:`Enum` subclass
        :param impl: Actual SQL type for the database side
        """
        if not issubclass(enum, Enum):
            raise TypeError(
                "argument must be a Python enum class; got %r" % (enum,))
        if not ((isclass(impl) and issubclass(impl, TypeEngine))
                or isinstance(impl, TypeEngine)):
            raise TypeError(
                "argument must be an ORM type; got %r" % (impl,))

        self.enum = enum
        self.impl = impl

    def copy(self):
        return EnumType(self.enum, self.impl)

    def load_dialect_impl(self, dialect):
        return dialect.type_descriptor(self.impl)

    def process_bind_param(self, value, dialect):
        """:type value: ``self.enum``"""
        if value is None:
            return None
        return value.value

    def process_result_value(self, value, dialect):
        """:type value: ``self.impl``"""
        if value is None:
            return None
        return self.enum(value)