1 files changed, 75 insertions, 0 deletions
diff --git a/libs/sqlalchemy/engine/characteristics.py b/libs/sqlalchemy/engine/characteristics.py
new file mode 100644
index 000000000..c0feb000b
--- /dev/null
+++ b/libs/sqlalchemy/engine/characteristics.py
@@ -0,0 +1,75 @@
+from __future__ import annotations
+
+import abc
+import typing
+from typing import Any
+from typing import ClassVar
+
+if typing.TYPE_CHECKING:
+    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 connection to its default value."""
+
+    @abc.abstractmethod
+    def set_characteristic(
+        self, dialect: Dialect, dbapi_conn: DBAPIConnection, value: Any
+    ) -> None:
+        """set characteristic on the connection to a given value."""
+
+    @abc.abstractmethod
+    def get_characteristic(
+        self, dialect: Dialect, dbapi_conn: DBAPIConnection
+    ) -> Any:
+        """Given a DBAPI connection, get the current value of the
+        characteristic.
+
+        """
+
+
+class IsolationLevelCharacteristic(ConnectionCharacteristic):
+    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)