old_contents: from spack import *
  
  class Libxml2(Package):
      """Libxml2 is the XML C parser and toolkit developed for the Gnome
         project (but usable outside of the Gnome platform), it is free
         software available under the MIT License."""
      homepage = "http://xmlsoft.org"
      url      = "http://xmlsoft.org/sources/libxml2-2.9.2.tar.gz"
  
      version('2.9.2', '9e6a9aca9d155737868b3dc5fd82f788')
  
      variant('python', default=False, description='Enable Python support')
  
      extends('python', when='+python')
      depends_on('zlib')
      depends_on('xz')
  
      def install(self, spec, prefix):
          if '+python' in spec:
              python_arg = "--with-python=%s" % spec['python'].prefix
          else:
              python_arg = "--without-python"
  
          configure("--prefix=%s" % prefix,
                    python_arg)
  
          make()
          make("install")
  
new_contents: from spack import *
  import os
  
  class Libxml2(Package):
      """Libxml2 is the XML C parser and toolkit developed for the Gnome
         project (but usable outside of the Gnome platform), it is free
         software available under the MIT License."""
      homepage = "http://xmlsoft.org"
      url      = "http://xmlsoft.org/sources/libxml2-2.9.2.tar.gz"
  
      version('2.9.2', '9e6a9aca9d155737868b3dc5fd82f788')
  
      variant('python', default=False, description='Enable Python support')
  
      extends('python', when='+python', ignore=r'(bin.*$)|(include.*$)|(share.*$)|(lib/libxml2.*$)|(lib/xml2.*$)|(lib/cmake.*$)')
      depends_on('zlib')
      depends_on('xz')
  
      def install(self, spec, prefix):
          if '+python' in spec:
              site_packages_dir = os.path.join(prefix, 'lib/python%s.%s/site-packages' %(spec['python'].version[:2]))
              python_args = ["--with-python=%s" % spec['python'].prefix, "--with-python-install-dir=%s" % site_packages_dir]
          else:
              python_args = ["--without-python"]
  
          configure("--prefix=%s" % prefix,
                    *python_args)
  
          make()
          make("install")
  
subject: install python files to libxml2 prefix instead of python prefix and ignore non-python files when activating