code: def Mixed(*types):
      
      if len(types) < 2:
          raise ValueError("Mixed type requires at least 2 specific types")
  
      types = set(types) # dedupe
  
      class MixedType(type):
          def __instancecheck__(cls, instance):
              """Returns true if the given value is an instance of
              one of the types enclosed by this mixed type."""
              for mtype in types:
                  if isinstance(instance, mtype):
                      return True
              return False
  
      class Mixed(object):
          __metaclass__ = MixedType
  
      return Mixed
docs: Mixed type, used to indicate a field in a schema can be
      one of many types. Use as a last resort only.
      The Mixed type can be used directly as a class to indicate
      any type is permitted for a given field:
      `"my_field": {"type": Mixed}`
      It can also be instantiated with list of specific types the
      field may is allowed to be for more control:
      `"my_field": {"type": Mixed(ObjectId, int)}`