def bin_to_str(bin_str_arr):
    """
    Convert binary number in string to string
    :param bin_str_arr: str, whose length must be a multiple of 8
    :return: str
    """
    res = ''
    for i in range(0, len(bin_str_arr), 8):
        res += chr(int(bin_str_arr[i:i+8], 2))
    return res