Create initial 2.0 engine implementation

Implemented the SQLAlchemy 2 :func:`.future.create_engine` function which
is used for forwards compatibility with SQLAlchemy 2.   This engine
features always-transactional behavior with autobegin.

Allow execution options per statement execution.  This includes
that the before_execute() and after_execute() events now accept
an additional dictionary with these options, empty if not
passed; a legacy event decorator is added for backwards compatibility
which now also emits a deprecation warning.

Add some basic tests for execution, transactions, and
the new result object.   Build out on a new testing fixture
that swaps in the future engine completely to start with.

Change-Id: I70e7338bb3f0ce22d2f702537d94bb249bd9fb0a
Fixes: #4644

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index d070027c8..2d023c6a6 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -461,6 +461,17 @@ class Generative(HasMemoized):
         return s
 
 
+class InPlaceGenerative(HasMemoized):
+    """Provide a method-chaining pattern in conjunction with the
+    @_generative decorator taht mutates in place."""
+
+    def _generate(self):
+        skip = self._memoized_keys
+        for k in skip:
+            self.__dict__.pop(k, None)
+        return self
+
+
 class HasCompileState(Generative):
     """A class that has a :class:`.CompileState` associated with it."""