Author: Maciej Fijalkowski <fij...@gmail.com>
Branch: extradoc
Changeset: r3973:f6959a758880
Date: 2011-12-09 00:14 +0200
http://bitbucket.org/pypy/extradoc/changeset/f6959a758880/
Log: a draft
diff --git a/blog/draft/matplotlib.rst b/blog/draft/matplotlib.rst
new file mode 100644
--- /dev/null
+++ b/blog/draft/matplotlib.rst
@@ -0,0 +1,80 @@
+===================================
+Plotting using matplotlib from PyPy
+===================================
+
+**Big fat warning** This is just a proof of concept. It actually barely works.
+There are missing pieces left and right there were replaced with hacks so
+I can get this to run and show it's possible. Don't try that at home,
+especially your home. You have been warned.
+
+There was a lot of talking about PyPy not integrating well with the current
+scientific python ecosystem and numpypy (a numpy reimplementation on top
+of pypy) was dubbed "a fancy array library". I'm going to show it is possible.
+
+First, `the demo`_::
+
+ #!/usr/bin/env pypy
+
+ # numpy, pypy version
+ import numpypy as numpy
+ # DRAGONS LIVE THERE (fortunately hidden)
+ from embed.emb import import_mod
+
+ pylab = import_mod('matplotlib.pylab')
+
+ if __name__ == '__main__':
+ a = numpy.arange(100, dtype=int)
+ b = numpy.sin(a)
+ pylab.plot(a, b)
+ pylab.show()
+
+And you get:
+
+ XXX pic
+
+Now, how to reproduce it:
+
+* You need a PyPy without cpyext, I did not find a linker that would support
+ overriding symbols. Right now there are no nightlies like this, so you have
+ to compile it yourself, like::
+
+ ./translate.py -Ojit targetpypystandalone.py --withoutmod-cpyext
+
+ That would give you a PyPy that's unable to load some libraries like PIL, but
+ perfectly working otherwise.
+
+* Speaking of which, you need a reasonably recent PyPy.
+
+* The approach is generally portable, however the implementation is not. Works
+ on 64bit linux, would not bet for anything else.
+
+* You need to install python2.6, python2.6 development headers and have numpy
+ and matplotlib installed on that python.
+
+* You need a checkout of my `hacks directory`_ and put embedded on your
+ ``PYTHONPATH``, pypy checkout also has to be on the ``PYTHONPATH``.
+
+Er wait, what happened?
+-----------------------
+
+What didn't happen is we did not reimplement matplotlib on top of PyPy. What
+did happen is we run a CPython instance in PyPy using ctypes. We instantiate
+it and nicely follow `embedding`_ tutorial for CPython. Since numpy arrays
+are not movable, we're able to pass around an integer that's a pointer to array
+data and reconstruct it in the embedded interpreter. Hence with a relatively
+little effort we managed to reuse the sama array data on both sides to
+plot at array. Easy, no?
+
+This approach can be extended to support anything that's not too tied with
+python objects. SciPy and matplotlib both fall into the same category
+but probably the same strategy can be applied to anything, like GTK or QT.
+It's just a matter of extending a hack into a working library.
+
+To summarize, while we're busy making numpypy better and faster, it seems
+that all heavy lifting on the C side can be done using an embedded Python
+interpreter with relatively little effort. To get to that point, I spent
+a day and a half to learn how to embed CPython, with very little prior
+experience in the CPython APIs.
+
+Cheers,
+fijal
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