Generates instances from the sources using either cls.transform_args or transform_args
    argument if present.

def map(cls, sources, *, transform_args=None):
    """Generates instances from the sources using either cls.transform_args or transform_args
    argument if present.
    """
    for idx, source in enumerate(sources):
      try:
        yield cls.create(source, transform_args=transform_args)
      except Exception as ex:
        raise Exception("An error occurred with item {0}".format(idx)) from ex