[Python-Dev] Status of C compilers for Python on Windows

Nathaniel Smith njs at pobox.com
Fri Oct 10 02:53:42 CEST 2014

On Fri, Oct 10, 2014 at 1:29 AM, Victor Stinner
<victor.stinner at gmail.com> wrote:
> Hi,
> Windows is not the primary target of Python developers, probably
> because most of them work on Linux. Official Python binaries are
> currently built by Microsoft Visual Studio. Even if Python developers
> get free licenses thanks for Microsoft, I would prefer to use an open
> source compiler if it would be possible. So *anyone* can build Python
> from scatch. I don't like the requirement of having a license to build
> Python. The free version (Visual Studio Express) only supports 32-bit
> and doesn't support PGO build (Profile-Guided Optimizations, which are
> disabled if I remember correctly because of compiler bugs).
> I know that it's hard to replace Visual Studio. I don't want to do it
> right now, but I would like to discuss that with you.
> === Open Watcom
> Jeffrey Armstrong is working on the Python support of OpenWatcom(v2), see:
> http://lightningpython.org/
> https://bitbucket.org/ArmstrongJ/lightning-python
> This compiler was initially written on MS-DOS in 32-bit, but it now
> supports Windows and Linux as well. The 64-bit mode is new and
> experimental. The Open Watcom "v2" project is actively developed at:
> https://github.com/open-watcom/open-watcom-v2/
> On Linux, Open Watcom don't support dynamic linking. On Windows, it
> uses its own C library. I'm not sure that Open Watcom is the best
> choice to build Python on Windows.
> === MinGW
> Some people tried to compile Python. See for example:
> https://bitbucket.org/puqing/python-mingw
> We even got some patches:
> http://bugs.python.org/issue3871 (rejected)
> See also:
> https://stackoverflow.com/questions/15365249/build-python-with-mingw-and-gcc
> MinGW reuses the Microsoft C library and it is based on GCC which is
> very stable, actively developed, supports a lot of archiectures, etc.
> I guess that it should be possible to reuse third party GCC tools like
> the famous GDB debugger?

You may want to get in touch with Carl Kleffner -- he's done a bunch
of work lately on getting a mingw-based toolchain to the point where
it can build numpy and scipy. (This is pretty urgent for us because
(a) numerical work requires a BLAS library and the main competitive
open-source one -- OpenBLAS -- cannot be built by msvc because of asm
syntax issues, (b) msvc's fortran support is even worse than its C99
support.) Getting this working is non-trivial, since by default
mingw-compiled code depends on the GCC runtime libraries, the default
ABI doesn't match msvc, etc. But apparently these issues are all

General info:

The built toolchains etc.:


The patch to the numpy sources -- this in particular includes the
various distutils hacks needed to enable the crucial ABI-compatibility

(Unfortunately he doesn't seem to have posted the build recipe for the
toolchain itself -- I'm sure he'd be happy to if you asked though.)

AFAICT the end result is a single free compiler toolchain that can
spit out 32- and 64-bit binaries using whichever MSVC runtime you


Nathaniel J. Smith
Postdoctoral researcher - Informatics - University of Edinburgh

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