Use external python for configuration variables.

SCons might be run by a different python than for which we install.
Run env['python'] to determine NumPy paths and distutils build names.

Author: pavoljuhas

SConstruct

@@ -31,14 +31,18 @@ def getsyspaths(*names):
     s = os.pathsep.join(filter(None, map(os.environ.get, names)))
     return filter(os.path.exists, s.split(os.pathsep))
 
-def pyconfigvar(name):
-    cmd = [env['python'], '-c', '\n'.join((
-            'from distutils.sysconfig import get_config_var',
-            'print get_config_var(%r)' % name))]
-    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
+def pyoutput(cmd):
+    proc = subprocess.Popen([env['python'], '-c', cmd],
+            stdout=subprocess.PIPE)
     out = proc.communicate()[0]
     return out.rstrip()
 
+def pyconfigvar(name):
+    cmd = '\n'.join((
+            'from distutils.sysconfig import get_config_var',
+            'print get_config_var(%r)' % name))
+    return pyoutput(cmd)
+
 # copy system environment variables related to compilation
 DefaultEnvironment(ENV=subdictionary(os.environ, '''
     PATH PYTHONPATH
@@ -123,7 +127,7 @@ if env['profile']:
 
 builddir = env.Dir('build/%s-%s' % (env['build'], platform.machine()))
 
-Export('env', 'pyconfigvar')
+Export('env', 'pyconfigvar', 'pyoutput')
 
 def GlobSources(pattern):
     """Same as Glob but also require that source node is a valid file.

srrealmodule/SConscript

@@ -1,13 +1,14 @@
 import sys
 import os
-from distutils.core import Distribution
-from distutils.command.build import build
 
-Import('env', 'GlobSources')
+Import('env', 'GlobSources', 'pyoutput')
 
 # make sure numpy headers are available
-from numpy.distutils.misc_util import get_numpy_include_dirs
-env.AppendUnique(CPPPATH=get_numpy_include_dirs())
+npdirs = pyoutput(
+    'from numpy.distutils.misc_util import get_numpy_include_dirs\n'
+    'print "\\n".join(get_numpy_include_dirs())')
+npdirs = map(str.strip, npdirs.split('\n'))
+env.AppendUnique(CPPPATH=npdirs)
 
 # configure the boost_python library, which may have different extensions
 if not (GetOption('clean') or env.GetOption('help')):
@@ -28,9 +29,14 @@ test = env.Alias('test', develop,
 AlwaysBuild(test)
 
 # normal install - trick distutils into using this module.
-bcmd = build(Distribution())
-bcmd.finalize_options()
-distmodfile = os.path.join(bcmd.build_platlib,
+build_platlib = pyoutput('\n'.join([
+    "from distutils.core import Distribution",
+    "from distutils.command.build import build",
+    "bcmd = build(Distribution())",
+    "bcmd.finalize_options()",
+    "print bcmd.build_platlib",
+    ]))
+distmodfile = os.path.join(build_platlib,
     'diffpy', 'srreal', os.path.basename(str(module[0])))
 cmd_install = '$python setup.py install'
 if 'prefix' in env: