Hi all,
It seems impossible to show a new console window with calling subprocess.Popen on windows with shell=True.

Attempt:
    si = subprocess.STARTUPINFO()
    si.dwFlags = subprocess.STARTF_USESHOWWINDOW
    si.wShowWindow = 5
    proc = Popen(
        cmd, cwd=runFolder, creationflags=subprocess.CREATE_NEW_CONSOLE, shell=True,
        startupinfo=si
    )

In the current source, it looks like this is due to the block in https://github.com/python/cpython/blob/master/Lib/subprocess.py#L1405 , which unreservedly wipes wShowWindow even if I have provided it.

Testing on Python 3.6 but I am assuming this affects all versions.

I think you have the right idea for improving the behavior here. It should skip setting wShowWindow if startupinfo already has the flag STARTF_USESHOWWINDOW. For example:

    if shell:
        comspec = os.environ.get("COMSPEC", "cmd.exe")
        args = '{} /c "{}"'.format (comspec, args)
        if not startupinfo.dwFlags & _winapi.STARTF_USESHOWWINDOW:
            startupinfo.dwFlags |= _winapi.STARTF_USESHOWWINDOW
            startupinfo.wShowWindow = _winapi.SW_HIDE