docs: def signature(self):
          """Create a signature for this method, only in Python > 3.4"""
          if not use_signature:
              raise NotImplementedError("Python 3 only.")
  
          if self.static:
              parameters = \
                  (Parameter(name='cls',
                             kind=Parameter.POSITIONAL_ONLY),)
  
          else:
              parameters = \
                  (Parameter(name='self',
                             kind=Parameter.POSITIONAL_ONLY),)
  
          if self.input_transform:
              return signature(self.input_transform)
  
          if self.uses_request:
              fields = get_fields(self.request_type)
              if not self.static:
                  if self.field_name not in fields:
                      raise NameError("field '{}' not found in {}".format(
                          self.field_name, self.request_name))
                  fields.remove(self.field_name)
              parameters += tuple(
                  Parameter(name=name, kind=Parameter.POSITIONAL_OR_KEYWORD,
                            default=None)
                  for name in fields)
  
          return Signature(parameters)