Add support for PostgreSQL with PyGreSQL

[Cito]

a description

[zzzeek]

looks good, how well do the tests run ? can you paste an output

[Cito]

Thanks for the quick feedback.

Did some manual testing and ran the standard test suite. Just noticed that the standard test suite only tests the default subdialect set as base.dialect (psycopg2 in this case). So I changed the base.dialect temporarily to pygresql, and ran the test suite again (is there a better was of testing this?). After fixing some issues (see above), the test suite now runs just was well with pygresql as with psycopg2.

I have two failing tests in DistinctEngineShardTest in both cases which seem to be unrelated. Shall I create an issue for these?

[zzzeek]

See the instructions for running the tests in README.unittests.rst. To run tests on any backend, use --dburi: py.test --dburi postgresql+pygresql://foo:bar@bat.

The DistinctEngineShardTest is a really old set of tests that only run against sqlite. I've not seen those fail in years so just show me the failure and I can likely tell you what's going on.

[Cito]

Ok, found the instructions and got everything working.

The issue with DistinctEngineShardTest seems to be caused by running the tests on a shared folder with vagrant, due to the vboxfs filesystem. When running from a real filesystem, everything worked properly.

I have run the test suite against a Postgres database with PyGreSQL 5.0 now.

Test results with Python 2:

py.test -x --dburi=postgresql+pygresql:///test

============================= test session starts ==============================
platform linux2 -- Python 2.7.6, pytest-2.8.7, py-1.4.31, pluggy-0.3.1 -- /home/vagrant/venv2-sqlalchemy/bin/python
cachedir: .cache
rootdir: /home/vagrant/sqlalchemy, inifile: setup.cfg
collecting ... collected 7577 items

test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_insert <- lib/sqlalchemy/testing/profiling.py SKIPPED
test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_select SKIPPED
test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_select_labels SKIPPED
...
test/sql/test_update.py::UpdateTest::test_update_preserve_order_reqs_listtups PASSED
test/sql/test_update.py::UpdateTest::test_update_to_expression PASSED
test/sql/test_update.py::UpdateTest::test_where_empty PASSED

================== 7052 passed, 525 skipped in 405.45 seconds ==================

Test results with Python 3:

py.test -x --dburi=postgresql+pygresql:///test

============================= test session starts ==============================
platform linux -- Python 3.4.3, pytest-2.8.7, py-1.4.31, pluggy-0.3.1 -- /home/vagrant/venv3-sqlalchemy/bin/python3
cachedir: .cache
rootdir: /home/vagrant/sqlalchemy, inifile: setup.cfg
collecting ... collected 7572 items

test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_insert SKIPPED
test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_select SKIPPED
test/aaa_profiling/test_compiler.py::CompileTest_postgresql_pygresql::test_select_labels SKIPPED
...
test/sql/test_update.py::UpdateTest::test_update_preserve_order_reqs_listtups PASSED
test/sql/test_update.py::UpdateTest::test_update_to_expression PASSED
test/sql/test_update.py::UpdateTest::test_where_empty PASSED

================== 7071 passed, 501 skipped in 405.59 seconds ==================

[zzzeek]

great! I'd merge this in for 1.1 which is hopefully in the spring, is that OK? (we've gone for ten years w/o a pygresql dialect so far whats another few months ? :) )

[Cito]

That's ok. A few months mean nothing to Pygres. It's already 21 years old :)

[zzzeek]

I likely will have to accept from #172 instead because I closed this person's PR about 8 months ago.

[zzzeek]

pygresql still inexplicably has private mailing list archives.

[zzzeek]

Dear contributor -

This pull request is being moved to Gerrit, at https://gerrit.sqlalchemy.org/36, where it may be tested and reviewed more closely. As such, the pull request itself is being marked "closed" or "declined", however your contribution is merely being moved to our central review system. Please register at https://gerrit.sqlalchemy.org#/register/ to send and receive comments regarding this item.