[IPython-dev] Extensible pretty-printing

Mark Voorhies mark.voorhies at ucsf.edu
Thu Oct 28 19:54:06 EDT 2010

On Thursday, October 28, 2010 04:11:18 pm Fernando Perez wrote:
> On Thu, Oct 28, 2010 at 4:00 PM, Robert Kern <robert.kern at gmail.com> wrote:
> > I recommend exactly what I did in ipwx. The DisplayTrap is configured with a
> > list of DisplayFormatters. Each DisplayFormatter gets a chance to decorate the
> > return messaged with an additional entry, keyed by the type of the
> > DisplayFormatter (probably something like 'string', 'html', 'image', etc. but
> > also perhaps 'repr', 'pretty', 'mathtext'; needs some more thought).

Would it make sense to use DisplayFormatter class names as keys?  That would
avoid name collisions.  Clients wanting more abstract/semantic formatting names
could use an auxiliary hierarchy of general->specific->formatter strings (e.g.,
provided by the pretty module) to find the best match to a target formatting
in the message (e.g., like resolving fonts in CSS).

> If the latter, I'm not sure I like the approach of passing a dict
> through and letting each formatter modify it.

Given that the outputs should be independent (i.e., shouldn't be modifying each
other), it seems like the main advantage of chaining the formatters would be to
avoid duplicating work (e.g., the html formatter could work off of the string result).
This could also be done by linking the formatters directly (e.g., passing a result-caching
string formatter to the html formatter's constructor) as long as we know the order that
they will be called in.


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