[issue37283] Unexpected behavior when running installer a second time with the same arguments or unattend.xml

[Jörn Jacobi]

New submission from Jörn Jacobi <jorn at geekware.dk>:

When executing the installer with arguments or using the unattend.xml to run it without UI as documented in https://python.readthedocs.io/en/stable/using/windows.html#installing-without-ui the installer ignores the arguments or unattend.xml when it's executed again.

The second time, the installer (running i modify mode) uses the default values (hereby removing the Prepenpath if set the first time)

(testet with version 3.6.6-amd64 to 3.7.3-amd64 of the executable installer)

To recreate, run the following : 

step 1 :
python-3.6.6-amd64.exe /passive InstallAllUsers=1 PrependPath=1 Include_doc=0 Include_dev=0 Include_tcltk=0 Include_test=0 SimpleInstall=1 

now python is install as expected.

step 2 : 
python-3.6.6-amd64.exe /passive InstallAllUsers=1 PrependPath=1 Include_doc=0 Include_dev=0 Include_tcltk=0 Include_test=0 SimpleInstall=1

even though the options are exactly the same, the installer now removes python from path and installs tcltk, documentation, test and dev.

step 3 : 
python-3.6.6-amd64.exe /passive InstallAllUsers=1 PrependPath=1 Include_doc=0 Include_dev=0 Include_tcltk=0 Include_test=0 SimpleInstall=1

now the installer only makes a quick check, what i would have expected in step 2, but hare only the default values are used.

----------
components: Installation
messages: 345589
nosy: Jörn Jacobi
priority: normal
severity: normal
status: open
title: Unexpected behavior when running installer a second time with the same arguments or unattend.xml
type: behavior
versions: Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37283>
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