subprocess.Popen: impossible to show console window when shell=True

[akdor1154]

BPO	40851
Nosy	@pfmoore, @tjguk, @zware, @eryksun, @zooba, @ZackerySpytz, @akdor1154
PRs	gh-85028: Don't set wShowWindow if startupinfo has STARTF_USESHOWWINDOW #20975

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-06-03.04:54:30.637>
labels = ['3.8', '3.9', '3.10', 'type-feature', 'library', 'OS-windows']
title = 'subprocess.Popen: impossible to show console window when shell=True'
updated_at = <Date 2020-06-19.05:53:00.466>
user = 'https://github.com/akdor1154'

bugs.python.org fields:

activity = <Date 2020-06-19.05:53:00.466>
actor = 'ZackerySpytz'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'Windows']
creation = <Date 2020-06-03.04:54:30.637>
creator = 'akdor1154'
dependencies = []
files = []
hgrepos = []
issue_num = 40851
keywords = ['patch']
message_count = 2.0
messages = ['370639', '370641']
nosy_count = 7.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'eryksun', 'steve.dower', 'ZackerySpytz', 'akdor1154']
pr_nums = ['20975']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40851'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[akdor1154]

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.

[eryksun]

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