def OC_calc(TP, TOP, P):
    """
    Calculate OC (Overlap coefficient).

    :param TP: true positive
    :type TP : int
    :param TOP: test outcome positive
    :type TOP : int
    :param P:  condition positive
    :type P : int
    :return: overlap coefficient as float
    """
    try:
        overlap_coef = TP / min(TOP, P)
        return overlap_coef
    except (ZeroDivisionError, TypeError):
        return 'None'
