subfigures missing bbox_inches attribute in inline backend

[story645]

Bug report

Trying to add subplots to subfigures when using the jupyter inline backend triggers a missing bbox error. Specifically this code,

%matplotlib inline
import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True, figsize=(10, 4))
subfigs = fig.subfigures(2, wspace=0.07)
axsLeft = subfigs[0].subplots()

where the backend complains AttributeError: 'SubFigure' object has no attribute 'bbox_inches'

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
~\Anaconda3\envs\mplrelease\lib\site-packages\IPython\core\formatters.py in __call__(self, obj)
    339                 pass
    340             else:
--> 341                 return printer(obj)
    342             # Finally look for special method names
    343             method = get_real_method(obj, self.print_method)

~\Anaconda3\envs\mplrelease\lib\site-packages\IPython\core\pylabtools.py in <lambda>(fig)
    246 
    247     if 'png' in formats:
--> 248         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    249     if 'retina' in formats or 'png2x' in formats:
    250         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))

~\Anaconda3\envs\mplrelease\lib\site-packages\IPython\core\pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    130         FigureCanvasBase(fig)
    131 
--> 132     fig.canvas.print_figure(bytes_io, **kw)
    133     data = bytes_io.getvalue()
    134     if fmt == 'svg':

~\Anaconda3\envs\mplrelease\lib\site-packages\matplotlib\backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
   2232             if bbox_inches:
   2233                 if bbox_inches == "tight":
-> 2234                     bbox_inches = self.figure.get_tightbbox(
   2235                         renderer, bbox_extra_artists=bbox_extra_artists)
   2236                     if pad_inches is None:

~\Anaconda3\envs\mplrelease\lib\site-packages\matplotlib\figure.py in get_tightbbox(self, renderer, bbox_extra_artists)
   1634 
   1635         for a in artists:
-> 1636             bbox = a.get_tightbbox(renderer)
   1637             if bbox is not None and (bbox.width != 0 or bbox.height != 0):
   1638                 bb.append(bbox)

~\Anaconda3\envs\mplrelease\lib\site-packages\matplotlib\figure.py in get_tightbbox(self, renderer, bbox_extra_artists)
   1653 
   1654         if len(bb) == 0:
-> 1655             return self.bbox_inches
   1656 
   1657         _bbox = Bbox.union(bb)

AttributeError: 'SubFigure' object has no attribute 'bbox_inches'

<Figure size 720x288 with 1 Axes>

[jklymak]

Just to keep ipython out of it:

import matplotlib.pyplot as plt

fig = plt.figure(constrained_layout=True, figsize=(10, 4))
subfigs = fig.subfigures(2, 1)
axsLeft = subfigs[0].subplots()
fig.savefig('Boo.png', bbox_inches='tight')

also triggers this error.

[jklymak]

Oh, humm, this is an interesting problem. bbox_inches='tight' is supposed to expand the figure to encompass all the artists. However, what does that mean for a subfigure? If I have a label or legend that overspills the subfigure, is the parent supposed to get larger to make room?

That seems too complicated, and I suspect for now the bbox should just be the hard bbox that is a fixed size.