<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def import_yaml(file_name, **kwargs):
 """ Imports curves and surfaces from files in YAML format. .. note:: Requires `ruamel.yaml <https://pypi.org/project/ruamel.yaml/>`_ package. Use ``jinja2=True`` to activate Jinja2 template processing. Please refer to the documentation for details. :param file_name: name of the input file :type file_name: str :return: a list of rational spline geometries :rtype: list :raises GeomdlException: an error occurred reading the file """

    def callback(data):
        yaml = YAML()
        return yaml.load(data)

    # Check if it is possible to import 'ruamel.yaml'
    try:
        from ruamel.yaml import YAML
    except ImportError:
        raise exch.GeomdlException("Please install 'ruamel.yaml' package to use YAML format: pip install ruamel.yaml")

    # Get keyword arguments
    delta = kwargs.get('delta', -1.0)
    use_template = kwargs.get('jinja2', False)

    # Read file
    file_src = exch.read_file(file_name)

    # Import data
    return exch.import_dict_str(file_src=file_src, delta=delta, callback=callback, tmpl=use_template)