python截取二进制文件

接到任务，截取dat文件，每个数据784个字节，现要取一定百分比的数据
主要涉及了python文件读写，命令行参数使用

# -*- coding: utf-8 -*-import sysimport osif __name__ == "__main__":    datPath = sys.argv[1]    pst = sys.argv[2]    k = float(pst)    datOut = datPath[0:-4]+str(k)+"%.dat"    k = k/100.0    try:        datIn = open(datPath,"rb")        datOut = open(datOut, "wb")    except Exception,e:        print e;        exit(-2)    size = os.path.getsize(datPath)    nIn = size/784    nOut = int(nIn*k)    try:        for i in range(0,nOut):            temp = datIn.read(784)            datOut.write(temp)    finally:        datIn.close()        datOut.close()