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Asked: 2026-05-11T12:42:39+00:00

I am trying to control a console application (JTAG app from Segger) from Python

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I am trying to control a console application (JTAG app from Segger) from Python using the subprocess module. The application behaves correctly for stdout, but stdin doesn’t seem to be read. If enable the shell, I can type into the input and control the application, but I need to do this programmatically. The same code works fine for issuing commands to something like cmd.exe.

I’m guessing that the keyboard is being read directly instead of stdin. Any ideas how I can send the application input?

from subprocess import Popen, PIPE, STDOUT jtag = Popen(''C:/Program Files/SEGGER/JLinkARM_V402e/JLink.exe'', shell=True,                         universal_newlines=True,                         stdin=PIPE,                         stdout=PIPE,                         stderr=STDOUT)  jtag.stdin.write('usb\n') jtag.stdin.flush()  print 'Stdout:' while True:     s = jtag.stdout.readline()     if not s:         break     print s,  jtag.terminate()
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1 Answer

  1. As shoosh says, I’d try to verify that the application really is looking for keyboard input. If it is, you can try Win32 message passing, or sending it keyboard input via automation.

    For the message passing route, you could use the EnumWindows function via ctypes to find the window you’re after, then using PostMessage to send it WM_KEYDOWN messages.

    You can also send keyboard input via pywinauto, or the ActiveX control of AutoIt via win32com.

    Using AutoIt:

    from win32com.client import Dispatch  auto = Dispatch('AutoItX3.Control') auto.WinActivate('The window's title', '') auto.WinWaitActive('The window's title', '', 10)  auto.Send('The input')
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