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✏️ Editing: characteristics.py

# engine/characteristics.py
# Copyright (C) 2005-2025 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
from __future__ import annotations

import abc
import typing
from typing import Any
from typing import ClassVar

if typing.TYPE_CHECKING:
    from .base import Connection
    from .interfaces import DBAPIConnection
    from .interfaces import Dialect

class ConnectionCharacteristic(abc.ABC):
    """An abstract base for an object that can set, get and reset a
    per-connection characteristic, typically one that gets reset when the
    connection is returned to the connection pool.

transaction isolation is the canonical example, and the
    ``IsolationLevelCharacteristic`` implementation provides this for the
    ``DefaultDialect``.

The ``ConnectionCharacteristic`` class should call upon the ``Dialect`` for
    the implementation of each method.   The object exists strictly to serve as
    a dialect visitor that can be placed into the
    ``DefaultDialect.connection_characteristics`` dictionary where it will take
    effect for calls to :meth:`_engine.Connection.execution_options` and
    related APIs.

.. versionadded:: 1.4

"""

__slots__ = ()

transactional: ClassVar[bool] = False

@abc.abstractmethod
    def reset_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> None:
        """Reset the characteristic on the DBAPI connection to its default
        value."""

@abc.abstractmethod
    def set_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
    ) -> None:
        """set characteristic on the DBAPI connection to a given value."""

def set_connection_characteristic(
        self,
        dialect: Dialect,
        conn: Connection,
        dbapi_conn: DBAPIConnection,
        value: Any,
    ) -> None:
        """set characteristic on the :class:`_engine.Connection` to a given
        value.

.. versionadded:: 2.0.30 - added to support elements that are local
           to the :class:`_engine.Connection` itself.

"""
        self.set_characteristic(dialect, dbapi_conn, value)

@abc.abstractmethod
    def get_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> Any:
        """Given a DBAPI connection, get the current value of the
        characteristic.

"""

def get_connection_characteristic(
        self, dialect: Dialect, conn: Connection, dbapi_conn: DBAPIConnection
    ) -> Any:
        """Given a :class:`_engine.Connection`, get the current value of the
        characteristic.

.. versionadded:: 2.0.30 - added to support elements that are local
           to the :class:`_engine.Connection` itself.

"""
        return self.get_characteristic(dialect, dbapi_conn)

class IsolationLevelCharacteristic(ConnectionCharacteristic):
    """Manage the isolation level on a DBAPI connection"""

transactional: ClassVar[bool] = True

def reset_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> None:
        dialect.reset_isolation_level(dbapi_conn)

def set_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
    ) -> None:
        dialect._assert_and_set_isolation_level(dbapi_conn, value)

def get_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> Any:
        return dialect.get_isolation_level(dbapi_conn)

class LoggingTokenCharacteristic(ConnectionCharacteristic):
    """Manage the 'logging_token' option of a :class:`_engine.Connection`.

.. versionadded:: 2.0.30

"""

transactional: ClassVar[bool] = False

def reset_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> None:
        pass

def set_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
    ) -> None:
        raise NotImplementedError()

def set_connection_characteristic(
        self,
        dialect: Dialect,
        conn: Connection,
        dbapi_conn: DBAPIConnection,
        value: Any,
    ) -> None:
        if value:
            conn._message_formatter = lambda msg: "[%s] %s" % (value, msg)
        else:
            del conn._message_formatter

def get_characteristic(
        self, dialect: Dialect, dbapi_conn: DBAPIConnection
    ) -> Any:
        raise NotImplementedError()

def get_connection_characteristic(
        self, dialect: Dialect, conn: Connection, dbapi_conn: DBAPIConnection
    ) -> Any:
        return conn._execution_options.get("logging_token", None)

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