def match_events(port, label):
    """ Find the given label in an event DataFrame

    Args:
        port (Port): The event port.
        label (str): The string to look for in the label column.

    Returns:
        DataFrame: The list of matched events, or `None` if there is no match.

    """
    matches = None
    if port.ready():
        matches = port.data[port.data['label'] == label]
        if matches.empty:
            matches = None
    return matches
