first add files

lib/sqlalchemy/engine/characteristics.py

@@ -0,0 +1,56 @@
+import abc
+
+from ..util import ABC
+
+
+class ConnectionCharacteristic(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 = False
+
+    @abc.abstractmethod
+    def reset_characteristic(self, dialect, dbapi_conn):
+        """Reset the characteristic on the connection to its default value."""
+
+    @abc.abstractmethod
+    def set_characteristic(self, dialect, dbapi_conn, value):
+        """set characteristic on the connection to a given value."""
+
+    @abc.abstractmethod
+    def get_characteristic(self, dialect, dbapi_conn):
+        """Given a DBAPI connection, get the current value of the
+        characteristic.
+
+        """
+
+
+class IsolationLevelCharacteristic(ConnectionCharacteristic):
+    transactional = True
+
+    def reset_characteristic(self, dialect, dbapi_conn):
+        dialect.reset_isolation_level(dbapi_conn)
+
+    def set_characteristic(self, dialect, dbapi_conn, value):
+        dialect.set_isolation_level(dbapi_conn, value)
+
+    def get_characteristic(self, dialect, dbapi_conn):
+        return dialect.get_isolation_level(dbapi_conn)