Fixed issue where :class:`.Index` object which contained a mixture of
functional expressions which were not resolvable to a particular column,
in combination with string-based column names, would fail to initialize
its internal state correctly leading to failures during DDL compilation.

Fixes: #4778
Change-Id: I0fa9c627a1fde92ba8b9ed10af167c156012bd5d

This is a very useful assertion which prevents unused variables
from being set up allows code to be more readable and sometimes
even more efficient.  test suites seem to be where the most
problems are and there do not seem to be documentation examples
that are using this, or at least the linter is not taking effect
within rst blocks.

Change-Id: I2b3341d8dd14da34879d8425838e66a4b9f8e27d

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

Fixed bug where a column-level :class:`.CheckConstraint` would fail
to compile the SQL expression using the underlying dialect compiler
as well as apply proper flags to generate literal values as
inline, in the case that the sqltext is a Core expression and
not just a plain string.   This was long-ago fixed for table-level
check constraints in 0.9 as part of :ticket:`2742`, which more commonly
feature Core SQL expressions as opposed to plain string expressions.

Change-Id: I1301ba4b40063e91bc47726aecc5f4990ffcaeda
Fixes: #3957

tested using pycodestyle version 2.2.0

Fixes: #3885
Change-Id: I5df43adc3aefe318f9eeab72a078247a548ec566
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/343

and test/sql/test_metadata IndexTest into
test/sql/test_metadata ConstraintTest

Change-Id: I7aeee9a1edbbd889200afc393695f73d5fbac3f3

:ticket:`3341` where in the unusual case of a constraint that refers
to a mixture of :class:`.Column` objects and string column names
at the same time, the auto-attach-on-column-attach logic will be
skipped; for the constraint to be auto-attached in this case,
all columns must be assembled on the target table up front.
Added a new section to the migration document regarding the
original feature as well as this change.
fixes #3411

applying any topological sort to tables on SQLite.  See the
changelog for details, but we now continue to sort
tables for SQLite on DROP, prohibit the sort from considering
alter, and only warn if we encounter an unresolvable cycle, in
which case, then we forego the ordering.  use_alter as always
is used to break such a cycle.
fixes #3378

and :class:`.CheckConstraint` has been further enhanced such that
when the constraint is associated with non-table-bound :class:`.Column`
objects, the constraint will set up event listeners with the
columns themselves such that the constraint auto attaches at the
same time the columns are associated with the table.  This in particular
helps in some edge cases in declarative but is also of general use.
fixes #3341