def mycopy(src_filename, dst_filename):

    try:

        fr = open(src_filename, "rb")

        try:

            try:

                fw = open(dst_filename, "wb")

                try:

                    while True:

                        b = fr.read(4096)

                        if not b:

                            break

                        fw.write(b)

                finally:

                    fw.close()

            except OSError:

                print("打开目标文件失败")

        finally:

            fr.close()

    except OSError:

        print("打开源文件失败")

src = input("请输入源文件名:")

dst = input("请输入目标文件:")

mycopy(src, dst)