from typing import List
import copy


def get_flow_keys(results: dict) -> List[str]:
    """Get keys of optical flow in results.

    Args:
        results (dict): The data that includes data and meta information and
            used in data augmentation pipeline.

    Returns:
        List: keys of optical flow in results.
    """
    flow_keys = []
    if 'ann_fields' in results:
        ann_keys = copy.deepcopy(results['ann_fields'])
        for k in ann_keys:
            if k.find('flow') > -1:
                flow_keys.append(k)
    return flow_keys