Add info about python dependencies

src/py/README.md

@@ -7,3 +7,93 @@
 cd crankshaft
 nosetests test/
 ```
+
+## Notes about python dependencies
+* This extension is targeted at production databases. Therefore certain restrictions must be assumed about the production environment vs other experimental environments.
+* We're using `pip` and `virtualenv` to generate a suitable isolated environment for python code that has  all the dependencies
+* Every dependency should be:
+  - Added to the `setup.py` file
+  - Installed through it
+  - Tested, when they have a test suite.
+  - Fixed in the `requirements.txt`
+* At present we use Python version 2.7.3
+
+---
+
+### Sample session with virtualenv
+#### Create and use a virtual env
+
+    # Create the virtual environment for python
+    $ virtualenv myenv
+
+    # Activate the virtualenv
+    $ source myenv/bin/activate
+
+    # Install all the requirements
+    # expect this to take a while, as it will trigger a few compilations
+    (myenv) $ pip install -r requirements.txt
+
+    # Add a new pip to the party
+    (myenv) $ pip install pandas
+
+#### Test the libraries with that virtual env
+##### Test numpy library dependency:
+
+    import numpy
+    numpy.test('full')
+
+output:
+```
+======================================================================
+ERROR: test_multiarray.TestNewBufferProtocol.test_relaxed_strides
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "/home/ubuntu/www/crankshaft/src/py/dev2/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
+    self.test(*self.arg)
+  File "/home/ubuntu/www/crankshaft/src/py/dev2/lib/python2.7/site-packages/numpy/core/tests/test_multiarray.py", line 5366, in test_relaxed_strides
+    fd.write(c.data)
+TypeError: 'buffer' does not have the buffer interface
+
+----------------------------------------------------------------------
+Ran 6153 tests in 84.561s
+
+FAILED (KNOWNFAIL=3, SKIP=5, errors=1)
+Out[2]: <nose.result.TextTestResult run=6153 errors=1 failures=0>
+```
+
+NOTE: this is expected to fail with Python 2.7.3, which is the version embedded in our postgresql installation
+
+
+##### Run scipy tests
+
+    import scipy
+    scipy.test('full')
+
+Output:
+```
+Ran 21562 tests in 321.610s
+
+OK (KNOWNFAIL=130, SKIP=1840)
+Out[2]: <nose.result.TextTestResult run=21562 errors=0 failures=0>
+```
+Ok, this looks good...
+
+##### Testing pysal
+See [http://pysal.readthedocs.org/en/latest/developers/testing.html]
+
+    import pysal
+    import nose
+    nose.runmodule('pysal')
+
+```
+Ran 537 tests in 42.182s
+
+FAILED (errors=48, failures=17)
+An exception has occurred, use %tb to see the full traceback.
+```
+
+This doesn't look good... Taking a deeper look at the failures, many have the `IOError: [Errno 2] No such file or directory: 'streets.shp'`
+
+In the source code, there's the following [config](https://github.com/pysal/pysal/blob/master/setup.cfg) that seems to be missing in the pip package. By copying it to `lib/python2.7/site-packages` within the environment, it goes down to 17 failures.
+
+The remaining failures don't look good. I see two types: precision calculation errors and arrays/matrices missing 1 element when comparing... TODO: FIX this