Creating a legend when `"legend.facecolor"` is set to `"inherit"` raises an error

[spencerkclark]

Description

I initially made a comment in #272, but this issue appears to be much more general. It seems that when using the default matplotlib style, and proplot axes that creating a legend raises an error.

Steps to reproduce

A "Minimal, Complete and Verifiable Example" will make it much easier for maintainers to help you.

import proplot
proplot.config.use_style("default")  # This line is key for the error
fig, ax = proplot.subplots(ncols=1, nrows=1)

ax.plot([0, 1], [0, 1], label="a")
ax.legend()

Expected behavior: [What you expected to happen]

No error.

Actual behavior: [What actually happened]

This error is raised:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-8-cd17e0d9dde1> in <module>
      4 
      5 ax.plot([0, 1], [0, 1], label="a")
----> 6 ax.legend()

~/proplot/proplot/axes/base.py in legend(self, handles, labels, loc, location, queue, **kwargs)
   2908             self._register_guide('legend', (handles, labels), loc, **kwargs)
   2909         else:
-> 2910             leg = self._draw_legend(handles, labels, loc=loc, **kwargs)
   2911             return leg
   2912 

~/proplot/proplot/axes/base.py in _draw_legend(self, handles, labels, loc, width, pad, space, align, frame, frameon, ncol, ncols, alphabetize, center, order, label, title, fontsize, fontweight, fontcolor, titlefontsize, titlefontweight, titlefontcolor, handle_kw, handler_map, **kwargs)
   2814             kwargs.update({key: kw_frame.pop(key) for key in ('shadow', 'fancybox')})
   2815             objs = [lax._parse_ordinary_legend(pairs, ncol=ncol, order=order, **kwargs)]
-> 2816             objs[0].legendPatch.update(kw_frame)
   2817         for obj in objs:
   2818             if hasattr(lax, 'legend_') and lax.legend_ is None:

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/artist.py in update(self, props)
   1004 
   1005         with cbook._setattr_cm(self, eventson=False):
-> 1006             ret = [_update_property(self, k, v) for k, v in props.items()]
   1007 
   1008         if len(ret):

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/artist.py in <listcomp>(.0)
   1004 
   1005         with cbook._setattr_cm(self, eventson=False):
-> 1006             ret = [_update_property(self, k, v) for k, v in props.items()]
   1007 
   1008         if len(ret):

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/artist.py in _update_property(self, k, v)
   1001                     raise AttributeError('{!r} object has no property {!r}'
   1002                                          .format(type(self).__name__, k))
-> 1003                 return func(v)
   1004 
   1005         with cbook._setattr_cm(self, eventson=False):

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/patches.py in set_facecolor(self, color)
    355         """
    356         self._original_facecolor = color
--> 357         self._set_facecolor(color)
    358 
    359     def set_color(self, c):

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/patches.py in _set_facecolor(self, color)
    343             color = mpl.rcParams['patch.facecolor']
    344         alpha = self._alpha if self._fill else 0
--> 345         self._facecolor = colors.to_rgba(color, alpha)
    346         self.stale = True
    347 

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/colors.py in to_rgba(c, alpha)
    183         rgba = None
    184     if rgba is None:  # Suppress exception chaining of cache lookup failure.
--> 185         rgba = _to_rgba_no_colorcycle(c, alpha)
    186         try:
    187             _colors_full_map.cache[c, alpha] = rgba

~/miniconda3/envs/fv3net/lib/python3.7/site-packages/matplotlib/colors.py in _to_rgba_no_colorcycle(c, alpha)
    259                     f"Value must be within 0-1 range")
    260             return c, c, c, alpha if alpha is not None else 1.
--> 261         raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
    262     # tuple color.
    263     c = np.array(c)

ValueError: Invalid RGBA argument: 'inherit'

Equivalent steps in matplotlib

Please make sure this bug is related to a specific proplot feature. If you're not sure, try to replicate it with the native matplotlib API. Matplotlib bugs belong on the matplotlib github page.

fig, ax = plt.subplots(1, 1)
ax.plot([0, 1], [0, 1], label="a")
ax.legend()

Proplot version

Paste the results of import matplotlib; print(matplotlib.__version__); import proplot; print(proplot.version)here.

3.2.2
0.9.5.post1

[spencerkclark]

A workaround for this is to explicitly set the "legend.facecolor" style parameter after setting the default matplotlib style:

import proplot
proplot.config.use_style("default")
proplot.rc["legend.facecolor"] = "white"
fig, ax = proplot.subplots(ncols=1, nrows=1)

ax.plot([0, 1], [0, 1], label="a")
ax.legend()

[danieldjewell]

@spencerkclark

I can confirm that this workaround works. FWIW, I'm also getting this error when using styles other than default...

e.g.

pplt.rc.reset()
pplt.rc.update({'style': 'seaborn-notebook'})
pplt.rc.update({'figure.dpi': 300,
               'meta.linewidth': 0.25, 
               'font.largesize': 8.0, 
               'font.smallsize': 6.0,
               'font.sans-serif': 'Noto Sans'})

[spencerkclark]

@danieldjewell indeed I think it will occur for any style that sets "legend.facecolor" to "inherit" rather than a specific color.

[lukelbd]

Thanks for the report! This was a very quick fix (now on master). A similar issue cropped up a while back when users tried making plots with rc['axes.titlecolor'] set to 'auto',

[spencerkclark]

Very nice, thanks!