(zzzeek:) For some reason I thought that threading.Lock() still did
not support context managers, at least in Python 2, however this
does not seem to be the case.

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Closes: #5069
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5069
Pull-request-sha: efeac06dda5afdbe33abcf9b27c8b5b5725c8444

Change-Id: Ic64fcd99cd587bc70b4ecc5b45d8205b5c76eff2

Change-Id: I08440dc25e40ea1ccea1778f6ee9e28a00808235

Change-Id: I6a71f4924d046cf306961c58dffccf21e9c03911

Applied on top of a pure run of black -l 79 in
I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9,  this set of changes
resolves all remaining flake8 conditions for those codes
we have enabled in setup.cfg.

Included are resolutions for all remaining flake8 issues
including shadowed builtins, long lines, import order, unused
imports, duplicate imports, and docstring issues.

Change-Id: I4f72d3ba1380dd601610ff80b8fb06a2aff8b0fe

This is a straight reformat run using black as is, with no edits
applied at all.

The black run will format code consistently, however in
some cases that are prevalent in SQLAlchemy code it produces
too-long lines.   The too-long lines will be resolved in the
following commit that will resolve all remaining flake8 issues
including shadowed builtins, long lines, import order, unused
imports, duplicate imports, and docstring issues.

Change-Id: I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9

Added new "lifo" mode to :class:`.QueuePool`, typically enabled by setting
the flag :paramref:`.create_engine.pool_use_lifo` to True.   "lifo" mode
means the same connection just checked in will be the first to be checked
out again, allowing excess connections to be cleaned up from the server
side during periods of the pool being only partially utilized.  Pull request
courtesy Taem Park.

Change-Id: Idb5e299c5082b3e6b547bd03022acf65fdc34f35
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/467

Change-Id: I3ef36bfd0cb0ba62b3123c8cf92370a43156cf8f

Change-Id: I4e8c2aa8fe817bb2af8707410fa0201f938781de