[IPython-dev] Architecting interactive matplotlib figures in the IPython notebook

Phil Elson pelson.pub@gmail....
Thu Apr 18 11:41:31 CDT 2013

You may be aware that as of matplotlib v1.3 there will be a "WebAgg"
backend which allows figures created on the server-side to be interacted
with on a client-side web browser.

Specifically calling *plt.show()* with the "WebAgg" backend starts a
tornado http server which serves up the open figures in PNG form. When the
client connects to the server, the current state of the figure is sent to
the browser, and any client mouse or keyboard interactions are captured and
sent back to the server via web sockets. Anything which result in a change
to the draw state are re-rendered, and the resulting PNG is sent back to
the client. This process works well for everything that we've tested,
including Pickers and Animations (I'd definitely encourage you to have a

So the obvious question is, can we use this technology to achieve
interactive figures in live IPython notebook environments?

Unfortunately I don't have enough knowledge of IPython's internals to make
the informed decisions necessary to get out of the blocks, so I'm hoping
the mailing list can help me out.
The first step towards this goal involves deciding *where* a (or multiple?)
WebAgg server(s) would sit. A couple of my thoughts on this (some of which
are mutually exclusive):

   - It'd be great to make use of the same twisted server as the Notebook
   client, so that we can piggy-back on the IPython notebook configuration
   (port, certificate etc.)
      - This would mean that this is a Notebook only feature (without this,
      there is no reason that other clients couldn't have implemented the
      necessary interface to achieve inline interactive figures (e.g., the Qt
      - This would also give the WebAgg the necessary blocking IOLoop to
      handle events and timers.
      - As of matplotlib v1.2 there has been experimental pickle support,
      - we are not bound to use the kernel that generated a figure in the
      first instance, as we can pass figures (albeit slowly) across processes
      - we could store the figure in the notebook format to be restored
      when a notebook is reconnected to a kernel (does this happen for other
      Display elements?)
      - As it stands, the WebAgg backend does not copy figure instances per
   client, so any interactions that one user does, is shown in every other
   client's browser. Is this a desirable feature for the Notebook? What about
   figures which are shown more than once in the same notebook?

I'm keen to work through these design decisions and am more than willing to
get my hands dirty - there is a matplotlib release scheduled for the end of
May, and myself and some of the other members of the matplotlib development
team are planning to attend SciPy with interactive figures for the Notebook
high on the wishlist.

Any thoughts on where you think the Agg server should sit and its expected
behaviour would be really valuable.

Thanks in advance,

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