How execute a .py in this way?

[Peter Hansen]

Peter Cai wrote:
> Thus, you
> can execute you "py" program anywhere by using the command "xxx.py",
> but when you want to use an exsiting file as it's input, you have to
> use something like "pythong xxx.py < input.txt".

This is apparently a bug or limitation of Windows command prompts and 
may not be fixed any time soon.  Past threads have discussed it and a 
recent one even gave pointers to some web pages that explain it further.

-Peter