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What's wrong on using Popen's communicate method?

Chris Angelico? 2019?7?4???? UTC+8??8?37?13????
> On Thu, Jul 4, 2019 at 10:01 AM <jfong at> wrote:
> >
> > I have the below. I expect to see 'abcd' showing in the notepad window:
> > ---------
> > import subprocess as sp
> > p0 = sp.Popen('notepad.exe', stdin=sp.PIPE)
> > p0.communicate(input=b'abcd')
> > ---------
> > But nothing happens. The notepad is completely empty. What have I missed?
> >
> The "communicate" method sends text to the standard input pipe. This
> has nothing to do with the GUI, and most Windows GUI programs take no
> notice of it. You'll need something GUI-aware for this.
> Is Notepad just an example, or are you actually trying to control MS Notepad?
> ChrisA

Yes, the notepad is just an example. My real attempt is to operate the external programs through Python. I know there are some "keyboard simulation" packages in Pypi which may work on this situation. But I prefer not bother to install them if Python's build-ins can do it.

By the way, after Popen invokes an external program, is there a way of making it on-foucs when there are multiple Popen instances?