[Python-Dev] Moving Python 3.5 on Windows to a new compiler

[Steve Dower]

Martin v. Löwis wrote:
> Am 06.06.14 22:13, schrieb Paul Moore:
>> From
>> http://www.visualstudio.com/en-us/downloads/visual-studio-14-ctp-vs
>>
>> """
>> Currently, Visual Studio "14" CTPs have known compatibility issues
>> with previous releases of Visual Studio and should not be installed
>> side-by-side on the same computer.
>> """
> 
> I also found
> 
> http://support.microsoft.com/kb/2967191
> 
> which is more specific about this issue:
> 
> '''There are known issues when you install Visual Studio "14" CTP
> 14.0.21730.1 DP on the same computer as Visual Studio 2013. While we expect that
> an uninstallation of Visual Studio "14" and then a repair of Visual Studio 2013
> should fix these issues, our safest recommendation is to install Visual Studio
> "14" in a VM, a VHD, a fresh computer, or another non-production test-only
> computer that does not have Visual Studio 2013 on it. All of these Visual Studio
> side-by-side issues are expected to be fixed soon.

Somebody ran a test to see how well the install/uninstall/repair scenario works, and it isn't that great. There are a lot of teams who contribute to Visual Studio, and not all of them have updated their installers yet (my team included...). Unfortunately, it all happened too close to the release to fix it for this version, hence the recommendation.

Eventually, VS 14 will be safe to install side-by-side with earlier versions. Chances are it is safe enough with VS 2010 or VS 2012 - it's the one-version-prior that's causing the most trouble.

> There is an installation block in this Visual Studio "14" CTP that will prevent
> installation on a computer where an earlier version of Visual Studio is already
> installed. To disable the block that will put the computer in an un-recommended
> state, add the value "BlockerOverride" to the registry:
> HKLM\SOFTWARE\Microsoft\DevDiv\vs\Servicing'''
> 
> So it seems to me that switching to VS 14 at this point in time is not possible.
> 
> Of course, Steve could certainly maintain a Mercurial clone in his hg.python.org
> sandbox that has all the necessary changes done, so people won't have to redo
> the porting over and over.

That's what I had in mind.

[Earlier post]
> 1. what is the availability of the compiler during the testing phase,
>    and what will it be immediately after the testing ends (where
>    traditionally people would have to buy licenses, or wait for VS
>    Express to be released)?

It's freely available now as part of Visual Studio, and all the pre-release releases will include everything. The last release (RC or whatever they decide to call it this time) should have a go-live license, though it will also be time bombed. I believe Express will be released at the same time as the paid versions.

> 2. what is the risk of installing a beta compiler on what might
>    otherwise be a "production" developer system? In particular, could
>    it interfere with other VS installations, and could it require a
>    complete system reinstall when the final release of VC 14 is
>    available?

Answered above. It's as risky as it always is, though as I mentioned, VC 14 may well be fine against VC 10.

Build-to-build upgrades may not be supported between pre-release versions, but typically RC to RTM upgrades are supported.

> 3. what is the chance of the final release being delayed beyond
>    the planned release date of Python 3.5? Microsoft has a bad
>    track record of meeting release dates (or the tradition of not
>    announcing any for that reason); the blog says that it will
>    be available "sometime in 2015". Now, Python 3.5 might appear
>    November 2015, so what do we do if VS 2015 is not released
>    by the time 3.5b1 is planned?

We keep the VS 2010 files around and make sure they keep working. This is the biggest risk of the whole plan, but I believe that there's enough of a gap between when VS 14 is planned to release (which I know, but can't share) and when Python 3.5 is planned (which I don't know, but have a semi-informed guess).

Is Python 3.5b1 being built with VS 14 RC (hypothetically) a blocking issue? Do we need to resolve that now or can it wait until it happens?

> Regards,
> Martin

Cheers,
Steve