Python. IOError: [Errno 13] Permission denied: 当我复制文件时

我有两个文件夹：In和Out - 它们不是D盘上的系统文件夹 - Windows 7。Out文件夹中包含“myfile.txt”文件。我在Python中运行以下命令：

>>> shutil.copyfile( r"d:\Out\myfile.txt", r"D:\In" )

Traceback (most recent call last):
  File "<pyshell#39>", line 1, in <module>
    shutil.copyfile( r"d:\Out\myfile.txt", r"D:\In" )
  File "C:\Python27\lib\shutil.py", line 82, in copyfile
    with open(dst, 'wb') as fdst:
IOError: [Errno 13] Permission denied: 'D:\\In'

有什么问题？