I installed python 2.6.3 on windows from .msi installer and get problem
to build ext modules with MinGW compiler.

It seems that Python 2.6.3 does not use compiler specified by user
via --compiler=xxx or setup.cfg on building ext module. Thus, MSVC
compiler is always used or show unreasonable error message
"error: Unable to find vcvarsall.bat" although specifying
--compiler=mingw32.

I found the change of r72594 cause this issue.

  [projects] Diff of
/python/branches/release26-maint/Lib/distutils/command/build_ext.py
 
http://svn.python.org/view/python/branches/release26-maint/Lib/distutils/command/build_ext.py?view=diff&r1=72593&r2=72594

And following patch get the behaviour like before, but I don't 
see why this change is introduced (merged from trunk).

{{{
diff -r 5874f642b473 distutils/command/build_ext.py
--- a/distutils/command/build_ext.py	Tue Oct 06 10:39:34 2009 +0900
+++ b/distutils/command/build_ext.py	Tue Oct 06 10:43:14 2009 +0900
@@ -303,7 +303,7 @@
 
         # Setup the CCompiler object that we'll use to do all the
         # compiling and linking
-        self.compiler = new_compiler(compiler=None,
+        self.compiler = new_compiler(compiler=self.compiler,
                                      verbose=self.verbose,
                                      dry_run=self.dry_run,
                                      force=self.force)

}}}

Is there any changes the way to specifying compiler?

Thanks for reporting this.

It appears that Benjamin tried to undo the .compiler attribute renaming
Tarek had applied and r72586, but forgot to change back line 303 to the
original version:

{{{
        # Setup the CCompiler object that we'll use to do all the
        # compiling and linking
        self.compiler = new_compiler(compiler=self.compiler,
                                     verbose=self.verbose,
                                     dry_run=self.dry_run,
                                     force=self.force)
}}}

Thanks for noticing, I'll rename it in the maintenance branch, but I
need to wait for Barry to give me the green light since the 2.6 branch
is frozen right now.

Tarek, please commit this fix before 2.6.4rc1 (i.e. asap :)

Done in r75269. Thanks Shun-ichi and Marc-André