On 2012/07/20 9:34 AM, Ryan May wrote:
> Hi,
>
> I'm here at the SciPy sprints trying to fix switching inline/gui for
> the ipython notebook. I've noticed something weird about
> matplotlib.use() :
>
> if 'matplotlib.backends' in sys.modules:
> if warn: warnings.warn(_use_error_msg)
> return
> if arg.startswith('module://'):
> name = arg
> else:
> # Lowercase only non-module backend names (modules are
> case-sensitive)
> arg = arg.lower()
> name = validate_backend(arg)
> rcParams['backend'] = name
>
> Notice the return if it finds the module loaded. This return basically
> makes it impossible to make use() have any effect one backends has
> been loaded. However, matplotlib.pyplot.switch_backend(). Eric added
> this in 2008 as a bug fix, but no more detail than that. Does anyone
> have a problem putting the return with the warning? Therefore if you
> pass warn=False, you can actually make the setting take effect, but
> the average user won't accidentally shoot their foot off. Something
> like:
>
> if 'matplotlib.backends' in sys.modules:
> if warn:
> warnings.warn(_use_error_msg)
> return
This would be defeating the basic idea: use() is *only* designed to take
effect *once*. If you need to switch backends, it takes more than what
use() does, hence the need for switch_backend(). (But see below.)
The warn=False invocation of use, with the return statement were it is
now, is for the case where you may have a script or module that
specifies a backend (in case it is the first or only import of
matplotlib), but that may itself be imported or called by something else
that has already imported matplotlib and set the backend. In this case
we want the warning to be suppressed, which is all the warn=False flag
is supposed to do. I use this myself.
So it looks like the problem is that switch_backends is broken because
what it needs matplotlib.use to do is go ahead and make the switch. This
could be done by adding a force=True kwarg (default would be False) to
matplotlib.use, or by deleting the reference to the backends module from
sys.modules in switch_backends before calling matplotlib.use. A
variation would be to use the force kwarg and to include the
switch_backends logic, or at least the reload line, in matplotlib.use.
That probably makes sense: add the force kwarg, and when the module is
replaced, reload it immediately within matplotlib.use. Then
pyplot.switch_backends only needs to do the pyplot-specific operations.
I think that is the cleanest solution.
Eric
>
>
> Ryan
>
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