The change in revision 42515 checks if MSSdk is
defined, and if so it will "Assume that the SDK set up
everything alright." The problem is that the SDK may be
set up for a different version of cl.exe than is
expected. In my case I have VC6 and VC7.1 installed and
the SDK is set up for VC6. When building extensions for
Python 2.5a2, distutils tries to use VC6 in my case.

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I don't understand the problem. MSSdk gets defined by
opening a specific SDK build environment. Just don't open
that build environment, but open a regular cmd.exe window,
and it should work fine.

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There is an option when installing VC (or at least there
used to be, I haven't checked lately) to set the environment
variables to take effect system wide. This is useful in that
the build environment is always available at any command
line (and they are also set when I build from my editor
which is not VS). I've left mine pointed at VC6 as I
typically do standalone DLLs using VC6 so they are easier to
redistribute. Distutils has always selected the right
version so it hasn't been an issue for me when working on
Python things before.

The issue wouldn't be as difficult if the resulting behavior
were more obvious. Unfortunately the initial errors in my
case were syntax errors arising from macro definitions that
changed between VC6 and VC7.1. Most of the time I spent
updating py2exe to work with 2.5 was spent on diagnosing
this. It wasn’t helped by the fact that I had a blind spot
regarding the compiler version. I use a batch file to build
py2exe for 2.3, then 2.4, and finally 2.5. Since 2.3 and 2.4
were building fine I didn’t even consider the idea of the
wrong compiler version being used for quite a while.

For now I just do "set MSSDK=" before building and then
everything works just fine.

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Here is a proposed patch: in addition to requiring MSSdk to
be set, distutils would also require DISTUTILS_USE_SDK to be
set.

Neal, can you please approve this new feature before beta 2?

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Martin, this looks fine if you think it's important.  Don't
forget to add a Misc/NEWS entry.

There are some typos in the doc:

chose -> choose

"most be both set" -> "must both be set"

Should the last distutils in the doc be:  \module{distutils}?

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Committed as r50509