def get_coord_labels(df):
    """Retrieve the coordinate labels from df.

    Parameters
    ----------
    df : pd.DataFrame
        DataFrame with each row being a geo location and two columns
        containing coordinate labels.

    Returns
    -------
    df_coord_labels : list | None
        Two entry list if coordinate labels are found:
        ['lat', 'lon'] or ['latitude', 'longitude']
    """
    df_coord_labels = None
    if 'lat' in df and 'lon' in df:
        df_coord_labels = ['lat', 'lon']
    elif 'latitude' in df and 'longitude' in df:
        df_coord_labels = ['latitude', 'longitude']
    return df_coord_labels
