[Python-Dev] 'Add/Remove Programs' entry missing for 'current user only' 32-bit installations on 64-bit Windows (original) (raw)

Jurko Gospodnetić jurko.gospodnetic at pke.hr
Mon Mar 17 22:10:28 CET 2014

Hi all.

This seems like it should be an 'old' issue, but I have not been able to find anything related to it on the web.

When you install 32-bit CPython 'for the current user only' on 64-bit Windows, the installation does not show up in the Windows 'Add/Remove Programs' dialog (a.k.a. 'Programs and Features' dialog on Windows 7). It does not show up there even for the current user.

As a consequence it is possible for the user to end up in a situation where it is impossible to install a 32-bit Python installation without manually cleaning up a previous 32-bit Python installation's Windows Installer related registry entries (more on this a bit later).

I tested this CPython installation behaviour with the following CPython versions:

Several related observations, indicating that this could be some sort of a Windows Installer misconfiguration issue possibly solvable in the CPython installer:

I started looking into this because I had a 32-bit CPython 3.4.0rc3 installation on my system that I wanted to remove, and since I did not see it registered in the 'Add/Remove Programs' dialog, I directly deleted its installation folder. That left my system in a state where a replacement 32-bit CPython 3.4.0 installation would always fail because it would detect that there was already a valid CPython 3.4 installation on the system, and then it would fail attempting to uninstall it. Fixing this required manually cleaning up leftover CPython 3.4.0rc3 windows installer registry entries. Note that the issue could not be fixed by using the CPython 3.4.0rc3 installer as it failed due to the same problem.

This situation would suggest that something should be done in the Windows installer so it does not 'fail miserably' if a previous CPython installation can not removed. Possibly allow it to detect that the previous CPython installation has already been removed and simply clean up its Windows Installer registry entries.

While working on this, I did discover a 'workaround' for the 'Add/Remove Programs' dialog issue, but it will take someone more knowledgeable about the Windows Installer infrastructure to say if the workaround can be applied directly as a clean solution or if it could have hidden consequences:

Each 32-bit installation on 64-bit Windows has its own 'Uninstall' registry key under:

HKEYLOCALMACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall

named after its Windows Installer assigned GUID, e.g.:

HKEYLOCALMACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall{A37F2D73-72D1-364D-BA5D-CEA430BCC040}

In that key there is a value named 'WindowsInstaller' which for CPython installations has the value '1' (of type REG_DWORD).

If you change that value to '0' (again, of type REG_DWORD), the installation's 'Add/Remove Programs' dialog entry will get displayed correctly, and user will be able to run the installation (reinstall/change/uninstall) from there.

I compared MSI packaging related CPython source code (Tools/msi folder) in 2.6.2 & 2.6.3 releases but I can not see anything suspicious there. It could be that the observed beaviour change between those two versions is a result of the final release packager changing his used Windows Installer version, but I have not rebuilt CPython, and its MSI installer to test this theory out.

Anyone have any more information on this?

Should I open a 'Add/Remove Programs' dialog related issue in the CPython issue tracker? And possibly a separate one for making CPython installations not fail without possible recovery if a previous CPython installation has already been removed?

Many thanks.

Best regards, Jurko Gospodnetić

P.S. All this has been tested using Windows 7 SP1 (x64).

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