Spack works with Python 3

- Update version guard in spack script to allow python 3
- Update min required version in the docs

README.md

@@ -23,7 +23,8 @@ See the
 [Feature Overview](http://spack.readthedocs.io/en/latest/features.html)
 for examples and highlights.
 
-To install spack and install your first package:
+To install spack and install your first package, make sure you have
+Python (2 or 3).  Then:
 
     $ git clone https://github.com/llnl/spack.git
     $ cd spack/bin

bin/spack

@@ -27,9 +27,9 @@
 from __future__ import print_function
 
 import sys
-if (sys.version_info[0] > 2) or (sys.version_info[:2] < (2, 6)):
+if sys.version_info[:2] < (2, 6):
     v_info = sys.version_info[:3]
-    sys.exit("Spack requires Python 2.6 or 2.7. "
+    sys.exit("Spack requires Python 2.6 or higher."
              "This is Python %d.%d.%d." % v_info)
 
 import os

lib/spack/docs/contribution_guide.rst

@@ -40,7 +40,7 @@ for the results of these tests after submitting a PR, we recommend that you run
 locally to speed up the review process.
 
 If you take a look in ``$SPACK_ROOT/.travis.yml``, you'll notice that we test
-against Python 2.6 and 2.7. We currently perform 3 types of tests:
+against Python 2.6, 2.7, and 3.3-3.6. We currently perform 3 types of tests:
 
 ^^^^^^^^^^
 Unit Tests

lib/spack/docs/getting_started.rst

@@ -11,7 +11,7 @@ Prerequisites
 Spack has the following minimum requirements, which must be installed
 before Spack is run:
 
-1. Python 2.6 or 2.7
+1. Python 2 (2.6 or 2.7) or 3 (3.3 - 3.6)
 2. A C/C++ compiler
 3. The ``git`` and ``curl`` commands.