Drop hard dependency on psycopg2 - require it anyway - closes sqlalch…

…emy-redshift#165 (sqlalchemy-redshift#172)

* Drop hard dependency on psycopg2 - require it anyway - closes sqlalchemy-redshift#165

    * Try to import psycopg2 raising ImportError with more descriptive message
    * add documentation warning about psycopg2

.gitignore

@@ -56,3 +56,6 @@ docs/_build/
 
 # PyBuilder
 target/
+
+# IDE
+.idea/

CHANGES.rst

@@ -1,6 +1,8 @@
 0.7.4 (unreleased)
 ------------------
 
+- Drop hard dependency on psycopg2 but require package to be present on runtime
+  (`Issue #165 <https://github.com/sqlalchemy-redshift/sqlalchemy-redshift/pull/165>`_)
 - Switch from info to keyword arguments on columns for ``SQLAlchemy >= 1.3.0``
   (`Issue #161 <https://github.com/sqlalchemy-redshift/sqlalchemy-redshift/pull/161>`_)
 - Add support for column info on redshift late binding views

README.rst

@@ -14,6 +14,17 @@ The package is available on PyPI::
 
     pip install sqlalchemy-redshift
 
+.. warning::
+
+    This dialect requires psycopg2 library to work properly. It does not provide
+    it as required, but relies on you to select the psycopg2 distribution you need:
+
+    * psycopg2 - standard distribution of psycopg2, requires compilation so few system dependencies are required for it
+    * psycopg2-binary - already compiled distribution (no system dependencies are required)
+    * psycopg2cffi - pypy compatible version
+
+    See `Psycopg2's binary install docs <http://initd.org/psycopg/docs/install.html#binary-install-from-pypi>`_
+    for more context on choosing a distribution.
 Usage
 -----
 The DSN format is similar to that of regular Postgres::

setup.py

@@ -18,9 +18,6 @@
     package_data={'sqlalchemy_redshift': ['redshift-ca-bundle.crt']},
     python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*',
     install_requires=[
-        'psycopg2>=2.5',
-         # requires sqlalchemy.sql.base.DialectKWArgs.dialect_options, new in
-         # version 0.9.2
         'SQLAlchemy>=0.9.2,<2.0.0',
     ],
     extras_require={

sqlalchemy_redshift/__init__.py

@@ -1,4 +1,17 @@
-from pkg_resources import get_distribution
+from pkg_resources import get_distribution, parse_version
+
+try:
+    import psycopg2  # noqa: F401
+    if get_distribution('psycopg2').parsed_version < parse_version('2.5'):
+        raise ImportError('Minimum required version for psycopg2 is 2.5')
+        # requires sqlalchemy.sql.base.DialectKWArgs.dialect_options, new in
+        # version 0.9.2
+except ImportError:
+    raise ImportError(
+        'No module named psycopg2. Please install either '
+        'psycopg2 or psycopg2-binary package for CPython '
+        'or psycopg2cffi for Pypy.'
+    )
 
 __version__ = get_distribution('sqlalchemy-redshift').version
 

tox.ini

@@ -14,6 +14,7 @@ deps =
 [testenv:lint]
 deps =
     flake8==2.4.0
+    psycopg2
 commands=flake8 sqlalchemy_redshift tests
 
 [testenv:docs]