Showing a plot overwrites matplotlib global options

[mmezzarobba]

sage: from matplotlib import rcParams
sage: rcParams['font.family'] = 'serif'
sage: p = plot(sin, 0, 1)
sage: rcParams['font.family']
[u'serif']
sage: p.show() # or save(), or matplotlib()
Launched png viewer for Graphics object consisting of 1 graphics primitive
sage: rcParams['font.family']
[u'sans-serif']

I think this is because Graphics.matplotlib() always loads a matplotlib stylesheet—usually 'classic'—, but I'm not sure what the right thing to do would be.

[strogdon]

Probably any of the defaults in matplotlib/mpl-data/stylelib/classic.mplstyle if changed through rcParams[] will be overwritten if matplotlib is called. I don't know what would have happened prior to the matplotlib upgrade.

[strogdon]

Yes, prior to commit ​d109b7593e user changes via rcParams[] were not altered after calls to matplotlib.

[fbissey]

I had not tested that particular scenario I must say. I thought it would work, there may be an ordering issue. One of the issue that lead to the inclusion of that style in matplotlib calls is that the default style changed between 1.5.x and 2.1.x. I got comments that plots after the upgrade to 2.1.x were not looking very good.

Including the style restored the default of 1.5.x and restored the general quality of the plots.

In effect I have been torn between importing a style sheet before every graphics call and documenting it somewhere that you needed it for nice plots (how many graphics calls for the documentation? A few hundreds probably). Or just applying it blindly.

Anyway, I'll have to dig that code again to see what is the right thing to do to over-ride style sheet options. I added the option to change the style sheet but you want something more fine grained than that.

[mmezzarobba]

I really like the option to specify a style sheet, it is a great way to give more control to the user on the appearance of the plots at a low development effort and without duplicating the functionality of matplotlib. And it could be enough to document prominently that this is the recommended way to set matplotlib options in sage (at the moment, there are several answers on ask.sage that suggest using matplotlib.rc or similar).

[strogdon]

We could keep track of user changes. Something like

src/sage/plot/graphics.py

@@ -2527 +2527 @@
         if not isinstance(ticks, (list, tuple)):
             ticks = (ticks, None)
 
+        from matplotlib import rcParams, style
+
+        #  save rcParams changed by the user
+        userdefaults = rcParams.items()
+        style.use('default')
+        l = []
+        for i in range(0, len(userdefaults)):
+            if userdefaults[i] != rcParams.items()[i]:
+                l.append(userdefaults[i])
+
         import matplotlib.pyplot as plt
         if stylesheet not in plt.style.available:
             stylesheet = 'classic'
         plt.style.use(stylesheet)
+        #  add user changed rcParams to current stylesheet
+        for i in range(0, len(l)):
+            rcParams[l[i][0]] = l[i][1]
 
         from sage.symbolic.ring import SR
         if not isinstance(tick_formatter, (list, tuple)):  # make sure both formatters typeset or both don't
@@ -3005 +3018 @@
         for g in self._objects:
             g.set_options(old_opts[g])
 
+        #  switch to the 'default' stylesheet and add back user changed rcParams
+        style.use('default')
+        for i in range(0, len(l)):
+            rcParams[l[i][0]] = l[i][1]
+
         return figure
 
     def save_image(self, filename=None, *args, **kwds):

I'm not sure it is robust enough, particularly with how the user changes are added in. And it will increase overhead if there are a lot of user changes. Before the patch

sage: from matplotlib import rcParams
sage: rcParams['font.size']
10.0
sage: p = plot(sin, 0, 1)
sage: p.matplotlib()
<matplotlib.figure.Figure object at 0x7f76037d2490>
sage: rcParams['font.size']
12.0

and after the patch

sage: from matplotlib import rcParams
sage: rcParams['font.size']
10.0
sage: p = plot(sin, 0, 1)
sage: p.matplotlib()
<matplotlib.figure.Figure object at 0x7f1928dff410>
sage: rcParams['font.size']
10.0

[strogdon]

This

rcParams[l[i][0]] = l[i][1]

is not correct in all cases, in particular the l[i][1]. But at the least we should restore the defaults.

[strogdon]

Well, may better than I thought

sage: from matplotlib import rcParams, rc
sage: rc('font', size=9.0, family='serif')
sage: rcParams['font.family']
[u'serif']
sage: rcParams['font.size']
9.0
sage: p = plot(sin, 0, 1)
sage: p.matplotlib()
<matplotlib.figure.Figure object at 0x7f7ff24a2350>
sage: rcParams['font.family']
[u'serif']
sage: rcParams['font.size']
9.0