issue computing repr of `Figure`

Tái hiện traceback trong một notebook bằng %matplotlib widget, sau đó kiểm tra đường dẫn repr của Figure trong figure.py quanh các dòng 403-408, lambda formatter của IPython pylabtools và backend_webagg_core.py quanh set_cursor và send_event. Được xem là hoàn tất khi fig được hiển thị sau khi việc vẽ hoàn tất mà không xảy ra AttributeError liên quan đến manager trong quá trình render.

Due to https://github.com/matplotlib/matplotlib/pull/10292 during a save operation we temporarily remove the manager

%matplotlib widget
import matplotlib.pyplot as plt
plt.plot(range(5))
fig = plt.gcf()

## new cell
fig

and you will get a traceback that looks like:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
~/.virtualenvs/bleeding/lib/python3.9/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)

~/.virtualenvs/bleeding/lib/python3.9/site-packages/IPython/core/pylabtools.py in <lambda>(fig)
    242 
    243     if 'png' in formats:
--> 244         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    245     if 'retina' in formats or 'png2x' in formats:
    246         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))

~/.virtualenvs/bleeding/lib/python3.9/site-packages/IPython/core/pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    126 
    127     bytes_io = BytesIO()
--> 128     fig.canvas.print_figure(bytes_io, **kw)
    129     data = bytes_io.getvalue()
    130     if fmt == 'svg':

~/source/p/mpl-master/lib/matplotlib/backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, **kwargs)
   2058             if bbox_inches:
   2059                 if bbox_inches == "tight":
-> 2060                     renderer = _get_renderer(
   2061                         self.figure,
   2062                         functools.partial(

~/source/p/mpl-master/lib/matplotlib/backend_bases.py in _get_renderer(figure, print_method)
   1546     with cbook._setattr_cm(figure, draw=_draw):
   1547         try:
-> 1548             print_method(io.BytesIO())
   1549         except Done as exc:
   1550             figure._cachedRenderer, = exc.args

~/source/p/mpl-master/lib/matplotlib/backends/backend_agg.py in print_png(self, filename_or_obj, metadata, pil_kwargs, *args, **kwargs)
    533 
    534         else:
--> 535             FigureCanvasAgg.draw(self)
    536             renderer = self.get_renderer()
    537             with cbook._setattr_cm(renderer, dpi=self.figure.dpi), \

~/source/p/mpl-master/lib/matplotlib/backends/backend_agg.py in draw(self)
    391         self.renderer = self.get_renderer(cleared=True)
    392         # Acquire a lock on the shared font cache.
--> 393         with RendererAgg.lock, \
    394              (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
    395               else nullcontext()):

~/source/other_source/cpython/Lib/contextlib.py in __enter__(self)
    111         del self.args, self.kwds, self.func
    112         try:
--> 113             return next(self.gen)
    114         except StopIteration:
    115             raise RuntimeError("generator didn't yield") from None

~/source/p/mpl-master/lib/matplotlib/backend_bases.py in _wait_cursor_for_draw_cm(self)
   2732         if self._draw_time - last_draw_time > 1:
   2733             try:
-> 2734                 self.set_cursor(cursors.WAIT)
   2735                 yield
   2736             finally:

~/source/p/mpl-master/lib/matplotlib/backends/backend_webagg_core.py in set_cursor(self, cursor)
    379     def set_cursor(self, cursor):
    380         if cursor != self.cursor:
--> 381             self.canvas.send_event("cursor", cursor=cursor)
    382         self.cursor = cursor
    383 

~/source/p/mpl-master/lib/matplotlib/backends/backend_webagg_core.py in send_event(self, event_type, **kwargs)
    344 
    345     def send_event(self, event_type, **kwargs):
--> 346         self.manager._send_event(event_type, **kwargs)
    347 
    348 

AttributeError: 'NoneType' object has no attribute '_send_event'

I thought we should be going through https://github.com/matplotlib/matplotlib/blob/59b5e0e873dd3420758498c90b15f7f70cb007da/lib/matplotlib/figure.py#L403-L408 but it looks like we are going trough a lambda from IPython core....

I think this could legitimately go against IPython, Matplotlib, or here. Leaving here as the "middle ground" ;)