Translating on Windows

RPython is supported on Windows platforms, starting with Windows 2000. The following text gives some hints about how to translate a interpreter written in RPython, using PyPy as an example.

To build pypy-c you need a working python environment, and a C compiler. It is possible to translate with a CPython 2.6 or 2.7, but this is not the preferred way, because it will take a lot longer to run – depending on your architecture, between two and three times as long. So head to our downloads and get the latest stable version.

Microsoft Visual Studio is preferred as a compiler, but there are reports of success with the mingw32 port of gcc.

What Compiler to use and How to find it?

The first stumbling block when building something for Python on windows is how to discover the path to the compiler, headers, and libraries. One can install many versions of the MSVC compiler tools, from stand-alone build tools to full blown Visual Studio IDE installations. Each of these use cases put the compiler at different locations, and the layout changes from time to time.

The distutils package, located in the stdlib, is the natural place to put this discovery code, but it is frozen by the python version. The pip- installable setuptools can move faster to adapt to new tools. So the first thing that will happen after building PyPy is it will install pip and download setuptools, then it will build the cffi modules used in stdlib. PyPy has a chicken and egg problem: in order to compile something we need setuptools, but in order to get setuptools we need pip which requires _ssl, and _ssl must be compiled. So PyPy vendors in a copy of in rpython/tools/

PyPy will prefer to compile with the latest MSVC compiler it can find, which is a departure from CPython’s desire to compile with the compiler used to compile the exe in use.

Translating PyPy with Visual Studio

We routinely test translation of PyPy using Visual Studio 2019, MSVC160. Other configurations may work as well. You must use at least Visual Studio 2012.

The translation scripts will set up the appropriate environment variables for the compiler, so you do not need to run vcvars before translation. They will pick the most recent Visual Studio compiler they can find. In addition, the target architecture (32 bits, 64 bits) is automatically selected. A 32 bit build can only be built using a 32 bit Python and vice versa. By default the interpreter is built using the Multi-threaded DLL (/MD) runtime environment.

If you wish to override this detection method to use a different compiler (mingw or a different version of MSVC):

  • set up the PATH and other environment variables as needed
  • set the CC environment variable to compiler exe to be used, for a different version of MSVC SET CC=cl.exe.

Note: The RPython translator requires a special 64 bit Python, see below

Python and a C compiler are all you need to build pypy, but it will miss some modules that relies on third-party libraries. See below how to get and build them.

Please see the non-windows instructions for more information, especially note that translation is RAM-hungry. A standard translation requires around 4GB, so special preparations are necessary, or you may want to use the following method to reduce memory usage at the price of a slower translation:

pypy --jit loop_longevity=300 ../../rpython/bin/rpython -Ojit targetpypystandalone
# This is done as part of translation
PYTHONPATH=../.. ./pypy-c ../../lib_pypy/pypy_tools/

Preparing Windows for the large build

Normally 32bit programs are limited to 2GB of memory on Windows. It is possible to raise this limit to almost 4GB on Windows 64bit.

You need to execute:

editbin /largeaddressaware translator.exe

where translator.exe is the pypy.exe or cpython.exe you will use to translate with. This is done by default during PyPy translation, so it should Just Work.

Installing external packages

We uses a subrepository inside pypy to hold binary compiled versions of the build dependencies for windows. As part of the rpython setup stage, environment variables will be set to use these dependencies. The repository has a README file on how to replicate, and a branch for each supported platform. You may run the utility to checkout the proper branch for your platform and PyPy version.

Using the mingw compiler

You can compile an RPython program with the mingw compiler, using the –cc=mingw32 option; gcc.exe must be on the PATH. If the -cc flag does not begin with “ming”, it should be the name of a valid gcc-derivative compiler, i.e. x86_64-w64-mingw32-gcc for the 64 bit compiler creating a 64 bit target.

You probably want to set the CPATH, LIBRARY_PATH, and PATH environment variables to the header files, lib or dlls, and dlls respectively of the locally installed packages if they are not in the mingw directory heirarchy.

libffi for the mingw compiler

To enable the _rawffi (and ctypes) module, you need to compile a mingw version of libffi. Here is one way to do this, wich should allow you to try to build for win64 or win32:

  1. Download and unzip a mingw32 build or mingw64 build, say into c:mingw

  2. If you do not use cygwin, you will need msys to provide make, autoconf tools and other goodies.

    1. Download and unzip a msys for mingw, say into c:msys
    2. Edit the c:msysetcfstab file to mount c:mingw
  3. Download and unzip the libffi source files, and extract them in the base directory.

  4. Run c:msysmsys.bat or a cygwin shell which should make you feel better since it is a shell prompt with shell tools.

  5. From inside the shell, cd to the libffi directory and do:

    sh ./configure
    cp .libs/libffi-5.dll <somewhere on the PATH>

If you can’t find the dll, and the libtool issued a warning about “undefined symbols not allowed”, you will need to edit the libffi Makefile in the toplevel directory. Add the flag -no-undefined to the definition of libffi_la_LDFLAGS

If you wish to experiment with win64, you must run configure with flags:

sh ./configure --build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32

or such, depending on your mingw64 download.

Hacking on PyPy with the mingw compiler

Since hacking on PyPy means running tests, you will need a way to specify the mingw compiler when hacking (as opposed to translating). As of March 2012, –cc is not a valid option for However if you set an environment variable CC to the compiler exe, testing will use it.

What is missing for a full 64-bit translation

This is a placeholder for old links to this topic. We have solved the 64-bit translation problems and there are nightly builds of 64-bit windows.