Extract field value from document
    :param input:
    :param params:
    :return:

def extract(input, **params):
    """
    Extract field value from document
    :param input:
    :param params:
    :return:
    """
    EXTRACT_FIELD = 'field'

    extract_params = params
    extract_params.update({AccessParams.KEY_TYPE: AccessParams.TYPE_SINGLE})
    return __extract(input, params)[params.get(EXTRACT_FIELD)]