fully implement future engine and remove legacy

The major action here is to lift and move future.Connection
and future.Engine fully into sqlalchemy.engine.base.   This
removes lots of engine concepts, including:

* autocommit
* Connection running without a transaction, autobegin
  is now present in all cases
* most "autorollback" is obsolete
* Core-level subtransactions (i.e. MarkerTransaction)
* "branched" connections, copies of connections
* execution_options() returns self, not a new connection
* old argument formats, distill_params(), simplifies calling
  scheme between engine methods
* before/after_execute() events (oriented towards compiled constructs)
  don't emit for exec_driver_sql().  before/after_cursor_execute()
  is still included for this
* old helper methods superseded by context managers, connection.transaction(),
  engine.transaction() engine.run_callable()
* ancient engine-level reflection methods has_table(), table_names()
* sqlalchemy.testing.engines.proxying_engine

References: #7257

Change-Id: Ib20ed816642d873b84221378a9ec34480e01e82c

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/sqlalchemy/event/legacy.py b/lib/sqlalchemy/event/legacy.py
index 0dbf69504..f75ed121f 100644
--- a/lib/sqlalchemy/event/legacy.py
+++ b/lib/sqlalchemy/event/legacy.py
@@ -14,6 +14,17 @@ from .. import util
 
 
 def _legacy_signature(since, argnames, converter=None):
+    """legacy sig decorator
+
+
+    :param since: string version for deprecation warning
+    :param argnames: list of strings, which is *all* arguments that the legacy
+     version accepted, including arguments that are still there
+    :param converter: lambda that will accept tuple of this full arg signature
+     and return tuple of new arg signature.
+
+    """
+
     def leg(fn):
         if not hasattr(fn, "_legacy_signatures"):
             fn._legacy_signatures = []