[Numpy-discussion] [ANN] Cell magics in IPython master

Fernando Perez fperez.net at gmail.com
Sun May 27 03:08:35 EDT 2012

Hi folks,

[ Sorry for the slightly off-topic post, but I know that a number of
people on this list have long wanted more seamless ways to integrate
with tools like Cython and R, and you may not necessarily follow the
ipython lists...]

I'm excited to report that we now have cell magics in IPython... PR
1732 [1] has just been merged [2], which implements the design
discussed in IPEP 1 [3]. This is probably one of the largest PRs we've
had so far, with over 100 commits, over 100 comments and a diff that's
almost 11000 lines long (a lot of it moving code around, obviously
it's not all new code).  But it brings two very important thigns:

1) a refactor of the magic system to finally remove the old mixin
class we'd had since the very first days of IPython in 2001.  This is
a cleanup I've been wanting to do for over 10 years!  The new setup
makes the magic system have  a very clean api, that is easy to use
both for the implementation of core features and for users to create
their own magics.

2) the new concept of cell magics: these are magics that get not only
the line they're on, but the entire cell body as well.  And while
these are most naturally used in the notebook, as you would expect
we've built them at the core of IPython, so you can use them with all
the clients (terminal, qt console, notebook).  For example, this is a
Cython magic that Brian just prototyped out (we'll have a production
version of it soon included).  Note that this was copied *from a
regular text terminal*, not from the notebook:

In [3]: from IPython.core.magic import register_line_cell_magic

In [4]: @register_line_cell_magic
   ...: def cython(line, cell):
   ...:     """Compile and import a cell as a .pyx file."""
   ...:     import sys
   ...:     from importlib import import_module
   ...:     module = line.strip()
   ...:     fname = module + '.pyx'
   ...:     with open(fname,'w') as f:
   ...:         f.write(cell)
   ...:     if 'pyximport' not in sys.modules:
   ...:         import pyximport
   ...:         pyximport.install(reload_support=True)
   ...:     globals()[module] = import_module(module)

In [5]: %%cython bam
   ...: def f(x):
   ...:     return 2.0*x

In [6]: bam.f(10)
Out[6]: 20.0

In a similar spirit, Jonathan Taylor recently created one to call R
transparently in the notebook:


This one hasn't been fully updated to the final API, but the core code
is there and now it should be a trivial matter to update it.

I want to thank everyone who pitched in with ideas during the
discussion and review period, and I hope you'll all enjoy this and
come up with great ways to use the system.  For now, you can see how
the system works by playing with %%timeit and %%prun, the only two
builtins that I extended to work also as cell magics.

For more details, see the documentation where we've added also a long
new section with details and examples of how to create your own [4].



[1] https://github.com/ipython/ipython/pull/1732
[2] https://github.com/ipython/ipython/commit/61eb2ffeebb91a94fe9befe2c30e7839781ddc52
[2] https://github.com/ipython/ipython/issues/1611
[3] http://ipython.org/ipython-doc/dev/interactive/reference.html#magic-command-system

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