I tried to build some extensions with python 2.6 (built from sources
with VS 2008 express), and got some errors in the function
query_vcvarsall. The offending lines are:

if len(result) != len(interesting):
    raise ValueError(str(list(result.keys())))

I got a value error here. After some investigation, I realized that it
was because I did not install the SDK. I think the error message could
be isgnificantly improved if installing the SDK was suggested in the
exception message.

Does it mean you won't get the settings for "include", "lib", "libpath"
and "path" when you call vcvarsall.bat *only* of the SDK is not
installed, or can't we have other cases ?

If the latter is true, maybe a better formatted Error message where
we list founded values and the list of missing values.

Hi tarek,

I can't say for sure about the only part. My experience on windows is
that there are so many possible combinations that getting it right is
difficult.

But in any case, the raised exception is not helpful. I am a developer
and familiar with distutils, and I could not make any sense of the
message. If the cause cannot be determined, at least a message like
"Unexpected result while detecting MS toolchain (str(result) vs
str(interesting)" would be helpful I think.

Also, but I am not 100 % sure about this, I believe any exception raised
within distutils should be inherited from DistutilsError

Improved msg per discussion.

I don't see how to test this without messing with the windows registry. I am deeply reluctant to do that.

( Upstreamed from Pip https://github.com/pypa/pip/issues/942 )

There are lot of Python users on Windows. If they succeed in installing a package manager (a struggle), this is typically their first experience with it

    $ pip install numpy

    blah blah blah

    Error: Unable to find vcvarsall.bat

The misery is compounded by the cryptic error message. They don't know whether the problem with their computer, the specific package, or pip generally. Let alone how to fix it.

You and I know this happens because the package install involves building some C code from source and the user doesn't have a C compiler installed. The fix is to install mingw32 (or Visual Studio) and edit distutils.cfg to specify to use that compiler. 

Thus, it would be really helpful to print a message after 'error: unable to find vcvarsall.bat' such as

> Installing this package requires a C compiler. To fix this error, follow http://stackoverflow.com/q/2817869/284795

For comparison, Ruby ships with a package manager, Gem. If a user tries to install a package with C extensions, they are given this user-friendly message:

> Please update your PATH to include build tools or download the DevKit from 'http://rubyinstaller.org/downloads' and follow the instructions at 'http://github.com/oneclick/rubyinstaller/wiki/Development-Kit'

How about "Error: vcvarsall.bat not found - VC++ not installed or wrong version" ?

On Python 3.3.3 it is even worse.
I am using Python 3.3.3 (32bit) on Windows 7 (64bit).
Visual Studio C++ 2008 Express Edition is properly installed.

Note: I use Python 32bit because Visual Studio C++ 2008 Express Edition includes only the 32bit compiler.

Using Google I did find the instructions on http://stackoverflow.com/q/2817869/284795
But they were of no help.

There are two problems that are not addressed.

Problem #1:
distutils/msvc9compiler.py decides to look for the 32bit registry key (because it is a 32bit Python) but it should look for the 64bit registry key (because it is a 64bit Windows).

Problem #2:
distutils/msvc9compiler.py decides to look for VERSION=10
I did some reverse engineering on the module to find this information.
Why is this not documented?

After setting VS100COMNTOOLS=%VS90COMNTOOLS% everything worked fine.

+1 vote for fixing this problem. Matt Hickford said it very well... the error message is very cryptic, not giving the user a clue as to what domain the problem lies in.

@Steve could this be included with the work you're doing with the Windows installers?

I can certainly improve this for 3.5 as part of the move to VC14 (which will require changes to distutils anyway). The installer won't touch it.

For earlier Python versions, I'd quite like to see setuptools take over detection from distutils and provide the better error message. I have some other work going on (currently, mostly, still in secret) that may help here, so I may be the one to contribute it to setuptools too if things go well.

error message should contain more details about what went wrong and why

please fix spent half a day to understand I need C compiler

The vsvarsall.bat message should direct to https://wiki.python.org/moin/WindowsCompilers rather than some 3rd-party site (even more so, one with user-generated content like SO).

E.g.: "Unable to find vcvarsall.bat. A required version of MS VC++ compilers is not installed or used improperly. See https://wiki.python.org/moin/WindowsCompilers for instructions."

I cannot understand the cryptic message could you please change it to something meaningful for "Unable to find vcvarsall.bat"

Idea: add a link to this article:
https://aka.ms/vcpython
or full link: https://blogs.msdn.microsoft.com/pythonengineering/2016/04/11/unable-to-find-vcvarsall-bat/

Related tweet from Steve Dower:
https://twitter.com/zooba/status/791032320006328320

@haypo, as I said, it's undesirable to link to a 3rd party site in a built-in error message because its availability and content are outside the dev team's control.

Maybe we can add an entry to the Python FAQ, use this link and then add a
link to the Microsoft article.

What's wrong with the Python wiki link in msg263206 above? It is supposed to be _the_ guide for setting up compilers in Windows, isn't it?

Ideally, this should be a link to `distutils' docs - because, you know, the wiki isn't carved in stone, either, while the docs for the specific version are bundled with it.

Actually, `distutils' does have an entry on `distutils.msvccompiler': https://docs.python.org/2/distutils/apiref.html#module-distutils.msvccompiler . It even documents the use of DUSTUTILS_USE_SDK variable!
The wording could use some clarification and maybe a link to wiki, but that's for another ticket.

Distutils is now deprecated (see PEP 632) and all tagged issues are being closed. From now until removal, only release blocking issues will be considered for distutils.

If this issue does not relate to distutils, please remove the component and reopen it. If you believe it still requires a fix, most likely the issue should be re-reported at https://github.com/pypa/setuptools