text: #  Copyright 2008-2015 Nokia Networks
  #  Copyright 2016-     Robot Framework Foundation
  #
  #  Licensed under the Apache License, Version 2.0 (the "License");
  #  you may not use this file except in compliance with the License.
  #  You may obtain a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  #  Unless required by applicable law or agreed to in writing, software
  #  distributed under the License is distributed on an "AS IS" BASIS,
  #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  #  See the License for the specific language governing permissions and
  #  limitations under the License.
  
  # Metaclass fix from http://code.activestate.com/recipes/204197-solving-the-metaclass-conflict/
  
  import inspect, types
  try:
      import __builtin__
  except ImportError:  # py3
      import builtins
  
  ############## preliminary: two utility functions #####################
  
  def skip_redundant(iterable, skipset=None):
      "Redundant items are repeated items or items in the original skipset."
      if skipset is None: skipset = set()
      for item in iterable:
          if item not in skipset:
              skipset.add(item)
              yield item
  
  
  def remove_redundant(metaclasses):
      skipset = set([types.ClassType])
      for meta in metaclasses: # determines the metaclasses to be skipped
          skipset.update(inspect.getmro(meta)[1:])
      return tuple(skip_redundant(metaclasses, skipset))
  
  ##################################################################
  ## now the core of the module: two mutually recursive functions ##
  ##################################################################
  
  memoized_metaclasses_map = {}
  
  def get_noconflict_metaclass(bases, left_metas, right_metas):
      """Not intended to be used outside of this module, unless you know
      what you are doing."""
      # make tuple of needed metaclasses in specified priority order
      metas = left_metas + tuple(map(type, bases)) + right_metas
      needed_metas = remove_redundant(metas)
  
      # return existing confict-solving meta, if any
      if needed_metas in memoized_metaclasses_map:
          return memoized_metaclasses_map[needed_metas]
      # nope: compute, memoize and return needed conflict-solving meta
      elif not needed_metas:         # wee, a trivial case, happy us
          meta = type
      elif len(needed_metas) == 1: # another trivial case
          meta = needed_metas[0]
      # check for recursion, can happen i.e. for Zope ExtensionClasses
      elif needed_metas == bases: 
          raise TypeError("Incompatible root metatypes", needed_metas)
      else: # gotta work ...
          metaname = '_' + ''.join([m.__name__ for m in needed_metas])
          meta = classmaker()(metaname, needed_metas, {})
      memoized_metaclasses_map[needed_metas] = meta
      return meta
  
  def classmaker(left_metas=(), right_metas=()):
      def make_class(name, bases, adict):
          metaclass = get_noconflict_metaclass(bases, left_metas, right_metas)
          return metaclass(name, bases, adict)
      return make_class
  
  