old_contents: import platform as py_platform
  from spack.architecture import OperatingSystem
  
  
  class MacOs(OperatingSystem):
      """This class represents the macOS operating system. This will be
      auto detected using the python platform.mac_ver. The macOS
      platform will be represented using the major version operating
      system name, i.e el capitan, yosemite...etc.
      """
  
      def __init__(self):
          """ Autodetects the mac version from a dictionary. Goes back as
              far as 10.6 snowleopard. If the user has an older mac then
              the version will just be a generic mac_os.
          """
          mac_releases = {'10.6': "snowleopard",
                          "10.7": "lion",
                          "10.8": "mountainlion",
                          "10.9": "mavericks",
                          "10.10": "yosemite",
                          "10.11": "elcapitan",
                          "10.12": "sierra"}
  
          mac_ver = py_platform.mac_ver()[0][:-2]
          name = mac_releases.get(mac_ver, "macos")
          super(MacOs, self).__init__(name, mac_ver)
  
      def __str__(self):
          return self.name
  
new_contents: import platform as py_platform
  from spack.architecture import OperatingSystem
  
  
  class MacOs(OperatingSystem):
      """This class represents the macOS operating system. This will be
      auto detected using the python platform.mac_ver. The macOS
      platform will be represented using the major version operating
      system name, i.e el capitan, yosemite...etc.
      """
  
      def __init__(self):
          """ Autodetects the mac version from a dictionary. Goes back as
              far as 10.6 snowleopard. If the user has an older mac then
              the version will just be a generic mac_os.
          """
          mac_releases = {'10.6': "snowleopard",
                          "10.7": "lion",
                          "10.8": "mountainlion",
                          "10.9": "mavericks",
                          "10.10": "yosemite",
                          "10.11": "elcapitan",
                          "10.12": "sierra"}
  
          mac_ver = '.'.join(py_platform.mac_ver()[0].split('.')[:2])
          name = mac_releases.get(mac_ver, "macos")
          super(MacOs, self).__init__(name, mac_ver)
  
      def __str__(self):
          return self.name
  
subject: fix MacOs class for Sierra (#1811)