Add immutabledict C code

Start trying to convert fundamental objects to
C as we now rely on a fairly small core of things,
and 1.4 is having problems with complexity added being
slower than the performance gains we are trying to build in.

immutabledict here does seem to bench as twice as fast as the
Python one, see below.  However, it does not appear to be
used prominently enough to make any dent in the performance
tests.

at the very least it may provide us some more lift-and-copy
code for more C extensions.

import timeit

from sqlalchemy.util._collections import not_immutabledict, immutabledict

def run(dict_cls):
    for i in range(1000000):
        d1 = dict_cls({"x": 5, "y": 4})

        d2 = d1.union({"x": 17, "new key": "some other value"}, None)

        assert list(d2) == ["x", "y", "new key"]

print(
    timeit.timeit(
        "run(d)", "from __main__ import run, not_immutabledict as d", number=1
    )
)
print(
    timeit.timeit(
        "run(d)", "from __main__ import run, immutabledict as d", number=1
    )
)

output:

python: 1.8799766399897635
C code: 0.8880784640205093

Change-Id: I29e7104dc21dcc7cdf895bf274003af2e219bf6d

1 files changed, 3 insertions, 2 deletions

diff --git a/test/engine/test_execute.py b/test/engine/test_execute.py
index 285dd2acf..fcf31b826 100644
--- a/test/engine/test_execute.py
+++ b/test/engine/test_execute.py
@@ -49,6 +49,7 @@ from sqlalchemy.testing.schema import Column
 from sqlalchemy.testing.schema import Table
 from sqlalchemy.testing.util import gc_collect
 from sqlalchemy.testing.util import picklers
+from sqlalchemy.util import collections_abc
 
 
 class SomeException(Exception):
@@ -1414,13 +1415,13 @@ class EngineEventsTest(fixtures.TestBase):
             conn, clauseelement, multiparams, params, execution_options
         ):
             assert isinstance(multiparams, (list, tuple))
-            assert isinstance(params, dict)
+            assert isinstance(params, collections_abc.Mapping)
 
         def after_execute(
             conn, clauseelement, multiparams, params, result, execution_options
         ):
             assert isinstance(multiparams, (list, tuple))
-            assert isinstance(params, dict)
+            assert isinstance(params, collections_abc.Mapping)
 
         e1 = testing_engine(config.db_url)
         event.listen(e1, "before_execute", before_execute)