legend.get_window_extent() fails

[durack1]

Bug summary

It seems a bug has crept in with points_to_pixels not available as a function called by get_window_extent

Code for reproduction

(Pdb) leg2 = plt.legend(loc='upper left', ncol=2, fontsize=8)
(Pdb) leg2.get_window_extent()
*** AttributeError: 'NoneType' object has no attribute 'points_to_pixels'
(Pdb) print(matplotlib.__version__)
3.4.2
(Pdb) print(matplotlib.get_backend())
MacOSX
(Pdb) import sys; print(sys.version_info)
sys.version_info(major=3, minor=9, micro=6, releaselevel='final', serial=0)
$ jupyter --version
jupyter core     : 4.7.1
jupyter-notebook : 6.4.0
qtconsole        : 5.1.1
ipython          : 7.25.0
ipykernel        : 6.0.1
jupyter client   : 6.1.12
jupyter lab      : not installed
nbconvert        : 6.1.0
ipywidgets       : 7.6.3
nbformat         : 5.1.3
traitlets        : 5.0.5

Actual outcome

Error, as above

Expected outcome

I expected to get coords

Operating system

MacOS 11.6

Matplotlib Version

3.4.2

Matplotlib Backend

MacOSX

Python version

3.9.6

Jupyter version

core 4.7.1; notebook 6.4.0

Other libraries

No response

Installation

conda

Conda channel

conda-forge

[jklymak]

get_window_extent has a renderer argument. Its optional for some methods and required by others. If it is set to None it uses the cached renderer, but that requires a draw to have been executed first. In this case you have no draw, so the call fails.

I'm skeptical this ever worked. If so, can you tell us what version? Maybe the renderer cache has changed in some way.

In the meantime, it is safest to call leg2.get_window_extent(fig.canvas.get_renderer()).

[QuLogic]

I believe this was fixed by #22745.