All the numpy python code has been imported into lib_pypy/numpy, from a random version of numpy (git version fd15162 to be exact). pypy has a builtin module called _numpypy that provides things like ndarray, dtypes, ufuncs, and binfuncs. The branch will be complete when it is possible to run pypy -c 'import numpy;numpy.test()' and most tests pass. The strategy for completing the branch is: 1. Set up pypy and cpython 2. Find missing functionality or a failing test 3. Fix and test Currently, 'import numpy' fails, since we are missing the c-level multiarray module. So what we need in the short-term is to implement a python version of multiarray, work has been begun and it lives in lib_pypy/numpypy/multiarray.py And in more detail: 1a. Get a recent trunk version of numpy 1a. Install numpy into python, for extra points use virtualenv, by running 'python setup.py install' in the numpy trunk 1c. Get the source tree for this branch of pypy 1d. Download a nightly build of pypy and put the binary into the source tree, preferably at pypy/translator/goal/pypy. Alternatively, translate pypy 2a. Run 'pypy/translator/goal/pypy -c 'import numpy;numpy.test()' 2b. Something will fail. Poke around to see what the missing function or import is supposed to do. Hint: try http://docs.scipy.org/doc/numpy/reference/index.html 2c. Let us know you are planning to work on this, usually a note on IRC will be sufficient. 2c. Write a test for the missing functionality. For instance, tests for multiarray live in lib_pypy/numpypy/test/test_multiarray.py Try to think of corner cases: inappropriate arguments, missing defaults, and other wierd combination of arguments. 3a. Try to find where numpy implemented it and stare at that till it makes sense. 3b. Write some code 3c. Test under pypy, python, and then think again about the tests, did you miss a corner case? Testing is done by: pypy/translator/pypy pytest.py lib_pypy/numpypy/test as well as python pytest.py lib_pypy/numpypy/test 3d. Rerun 2a to make sure you accomplished what you set out to do 3e. Commit and push your changes, if you are working on a fork let us know what you have done.