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import abc
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 = 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._assert_and_set_isolation_level(dbapi_conn, value)
def get_characteristic(self, dialect, dbapi_conn):
return dialect.get_isolation_level(dbapi_conn)
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