matplotlib-devel

[matplotlib-devel] matplotlib.use()

[Ryan M. <rm...@gm...>]

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


Ryan

-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma

Re: [matplotlib-devel] matplotlib.use()

[Eric F. <ef...@ha...>]

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
>

Re: [matplotlib-devel] matplotlib.use()

[Benjamin R. <ben...@ou...>]

On Fri, Jul 20, 2012 at 3:20 PM, Eric Firing <ef...@ha...> wrote:

> 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
>
>
I like the "force" idea very much.  It means exactly what it says.

Ben Root

Re: [matplotlib-devel] matplotlib.use()

[Ryan M. <rm...@gm...>]

On Fri, Jul 20, 2012 at 3:20 PM, Eric Firing <ef...@ha...> wrote:
> 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.

I agree, this is a better way to go. (And occurred to me as well after
the initial PR.)

Glad I asked rather than doing my 2-line fix. The updated PR is at
https://github.com/matplotlib/matplotlib/pull/1028

Ryan

--
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma