[New-bugs-announce] [issue34044] subprocess: reusing STARTUPINFO breaks under 3.7 (Windows)

[Sebastian Bank]

New submission from Sebastian Bank <sebastian.bank at uni-leipzig.de>:

AFAIU, the change for https://bugs.python.org/issue19764 broke the following usage of subprocess on Windows (re-using a subprocess.STARTUPINFO instance to hide the command window):

    import os, subprocess

    STARTUPINFO = subprocess.STARTUPINFO()
    STARTUPINFO.dwFlags |= subprocess.STARTF_USESHOWWINDOW
    STARTUPINFO.wShowWindow = subprocess.SW_HIDE

    # raises OSError: [WinError 87]
    # in the second loop iteration starting with Python 3.7
    for i in range(2):
        print(i)
        with open(os.devnull, 'w') as stderr:
            subprocess.check_call(['attrib'], stderr=stderr,
                                  startupinfo=STARTUPINFO)

AFAICT, this works on Python 2.7, 3.4, 3.5, and 3.6

I think the documentation in

https://docs.python.org/3/library/subprocess.html#windows-popen-helpers

does not mention that every Popen call should be done with a fresh instance, so either the documentation needs to be changed, or the implementation (e.g. by deep-copying the instance).

See also https://bugs.python.org/issue19764#msg320784

----------
components: Library (Lib)
messages: 321047
nosy: eryksun, vstinner, xflr6
priority: normal
severity: normal
status: open
title: subprocess: reusing STARTUPINFO breaks under 3.7 (Windows)
type: behavior
versions: Python 3.7

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<https://bugs.python.org/issue34044>
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