Applied an explicit "cause" to most if not all internally raised exceptions
that are raised from within an internal exception catch, to avoid
misleading stacktraces that suggest an error within the handling of an
exception.  While it would be preferable to suppress the internally caught
exception in the way that the ``__suppress_context__`` attribute would,
there does not as yet seem to be a way to do this without suppressing an
enclosing user constructed context, so for now it exposes the internally
caught exception as the cause so that full information about the context
of the error is maintained.

Fixes: #4849
Change-Id: I55a86b29023675d9e5e49bc7edc5a2dc0bcd4751

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

Change-Id: I3ef36bfd0cb0ba62b3123c8cf92370a43156cf8f

In release 1.1, the :class:`.Boolean` type was broken in that
boolean coercion via ``bool()`` would occur for backends that did not
feature "native boolean", but would not occur for native boolean backends,
meaning the string ``"0"`` now behaved inconsistently. After a poll, a
consensus was reached that non-boolean values should be raising an error,
especially in the ambiguous case of string ``"0"``; so the :class:`.Boolean`
datatype will now raise ``ValueError`` if an incoming value is not
within the range ``None, True, False, 1, 0``.

Change-Id: If70c4f79c266f0dd1a0306c0ffe7acb9c66c4cc3
Fixes: #4102

Corrects some warnings and adds tox config.  Adds DeprecationWarning
to the error category.   Large sweep for string literals w/ backslashes
as this is common in docstrings

Co-authored-by: Andrii Soldatenko
Fixes: #3886
Change-Id: Ia7c838dfbbe70b262622ed0803d581edc736e085
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/337

Change-Id: I4e8c2aa8fe817bb2af8707410fa0201f938781de

The processing performed by the :class:`.Boolean` datatype for backends
that only feature integer types has been made consistent between the
pure Python and C-extension versions, in that the C-extension version
will accept any integer value from the database as a boolean, not just
zero and one; additionally, non-boolean integer values being sent to
the database are coerced to exactly zero or one, instead of being
passed as the original integer value.

Change-Id: I01e647547fd7047bd549dd70e1fa202c51e8328b
Fixes: #3730