old_contents: import sys
  import itertools
  import inspect
  
  from collections import namedtuple
  
  _PY2 = sys.version_info.major == 2
  
  if _PY2:
  
      range_ = xrange
  
      zip_ = itertools.izip
  
      def iteritems(d):
          return d.iteritems()
  
      def itervalues(d):
          return d.itervalues()
  
      def iterkeys(d):
          return d.iterkeys()
  
      zip_longest = itertools.izip_longest
  
      def getargspec(f):
          return inspect.getargspec(f)
  
  else:
  
      range_ = range
  
      zip_ = zip
  
      def iteritems(d):
          return iter(d.items())
  
      def itervalues(d):
          return iter(d.values())
  
      def iterkeys(d):
          return iter(d.keys())
  
      zip_longest = itertools.zip_longest
  
      _ArgSpec = namedtuple('ArgSpec', ('args', 'varargs', 'keywords', 'defaults'))
  
      def getargspec(f):
          argspec = inspect.getfullargspec(f)
          # FullArgSpec(args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations)
  
          return _ArgSpec(argspec.args, argspec.varargs, argspec.varkw, argspec.defaults)
  
new_contents: # Most of this code is from the python six package, under the following license:
  #
  # Copyright (c) 2010-2018 Benjamin Peterson
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in all
  # copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  #
  
  import sys
  import itertools
  import inspect
  
  from collections import namedtuple
  
  _PY2 = sys.version_info.major == 2
  
  if _PY2:
  
      range_ = xrange
  
      zip_ = itertools.izip
  
      def iteritems(d):
          return d.iteritems()
  
      def itervalues(d):
          return d.itervalues()
  
      def iterkeys(d):
          return d.iterkeys()
  
      zip_longest = itertools.izip_longest
  
      def getargspec(f):
          return inspect.getargspec(f)
  
  else:
  
      range_ = range
  
      zip_ = zip
  
      def iteritems(d):
          return iter(d.items())
  
      def itervalues(d):
          return iter(d.values())
  
      def iterkeys(d):
          return iter(d.keys())
  
      zip_longest = itertools.zip_longest
  
      _ArgSpec = namedtuple('ArgSpec', ('args', 'varargs', 'keywords', 'defaults'))
  
      def getargspec(f):
          argspec = inspect.getfullargspec(f)
          # FullArgSpec(args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations)
  
          return _ArgSpec(argspec.args, argspec.varargs, argspec.varkw, argspec.defaults)
  
  
  def add_metaclass(metaclass):
      """Class decorator for creating a class with a metaclass."""
      def wrapper(cls):
          orig_vars = cls.__dict__.copy()
          slots = orig_vars.get('__slots__')
          if slots is not None:
              if isinstance(slots, str):
                  slots = [slots]
              for slots_var in slots:
                  orig_vars.pop(slots_var)
          orig_vars.pop('__dict__', None)
          orig_vars.pop('__weakref__', None)
          return metaclass(cls.__name__, cls.__bases__, orig_vars)
      return wrapper
  
subject: Add add_metaclass to dimod.compatibility23 from python six