docs: def available_method(method_name):
      '''ruturn the method for earliest package in ``pkg_preferences``, if package is available (based on :meth:`pkg_available`)'''
      pkg_prefs_copy = list(pkg_prefs)
      if method_name in method_prefs:
          pkg_prefs_copy = [method_prefs[method_name]] + pkg_prefs_copy
      for pkg in pkg_prefs_copy:
          if pkg in pkgs:
              if method_name in dir(pkgs[pkg]):
                  return getattr(pkgs[pkg],method_name)
      nl.notify('Error: Could not find implementation of %s on this computer' % (method_name),level=nl.level.error)