Add mock python package.

var/spack/repos/builtin.mock/packages/python/package.py

+##############################################################################
+# Copyright (c) 2013-2015, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License (as published by
+# the Free Software Foundation) version 2.1 dated February 1999.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
+# conditions of the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+class Python(Package):
+    """Dummy Python package to demonstrate preferred versions."""
+    homepage = "http://www.python.org"
+    url      = "http://www.python.org/ftp/python/2.7.8/Python-2.7.8.tgz"
+
+    extendable = True
+
+    version('3.5.1', 'be78e48cdfc1a7ad90efff146dce6cfe')
+    version('3.5.0', 'a56c0c0b45d75a0ec9c6dee933c41c36')
+    version('2.7.11', '6b6076ec9e93f05dd63e47eb9c15728b', preferred=True)
+    version('2.7.10', 'd7547558fd673bd9d38e2108c6b42521')
+    version('2.7.9', '5eebcaa0030dc4061156d3429657fb83')
+    version('2.7.8', 'd4bca0159acb0b44a781292b5231936f')
+
+    def install(self, spec, prefix):
+        pass
+