简单来说:

import sys
# parse command line
if file_name_given:
    inf = open(file_name_given)
else:
    inf = sys.stdin

此时您将使用 inf 从文件中读取.根据是否给定文件名，这将从给定的文件或标准输入读取.

At this point you would use inf to read from the file. Depending on whether a filename was given, this would read from the given file or from stdin.

当你需要关闭文件时，你可以这样做:

When you need to close the file, you can do this:

if inf is not sys.stdin:
    inf.close()

然而，在大多数情况下，如果你完成了关闭 sys.stdin 是无害的.

However, in most cases it will be harmless to close sys.stdin if you're done with it.