python-matplotlib fails to build with Python 3.9.0a2.

Error report:

=================================== FAILURES ===================================
_____________________________ test_pil_kwargs_tiff _____________________________
[gw2] linux -- Python 3.9.0 /usr/bin/python3

    def test_pil_kwargs_tiff():
        Image = pytest.importorskip("PIL.Image")
        from PIL.TiffTags import TAGS_V2 as TAGS
        buf = io.BytesIO()
        pil_kwargs = {"description": "test image"}
>       plt.figure().savefig(buf, format="tiff", pil_kwargs=pil_kwargs)

../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/tests/test_agg.py:260: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/figure.py:2180: in savefig
    self.canvas.print_figure(fname, **kwargs)
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/backend_bases.py:2021: in print_figure
    canvas = self._get_output_canvas(format)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <matplotlib.backends.backend_agg.FigureCanvasAgg object at 0x7f342dfa04f0>
fmt = 'tiff'

    def _get_output_canvas(self, fmt):
        """
        Return a canvas suitable for saving figures to a specified file format.
    
        If necessary, this function will switch to a registered backend that
        supports the format.
        """
        # Return the current canvas if it supports the requested format.
        if hasattr(self, 'print_{}'.format(fmt)):
            return self
        # Return a default canvas for the requested format, if it exists.
        canvas_class = get_registered_canvas_class(fmt)
        if canvas_class:
            return self.switch_backends(canvas_class)
        # Else report error for unsupported format.
>       raise ValueError(
            "Format {!r} is not supported (supported formats: {})"
            .format(fmt, ", ".join(sorted(self.get_supported_filetypes()))))
E       ValueError: Format 'tiff' is not supported (supported formats: eps, pdf, pgf, png, ps, raw, rgba, svg, svgz)

../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/backend_bases.py:1961: ValueError
________________________________ test_jpeg_dpi _________________________________
[gw0] linux -- Python 3.9.0 /usr/bin/python3

    @pytest.mark.backend('Agg')
    def test_jpeg_dpi():
        Image = pytest.importorskip("PIL.Image")
        # Check that dpi is set correctly in jpg files.
        plt.plot([0, 1, 2], [0, 1, 0])
        buf = io.BytesIO()
>       plt.savefig(buf, format="jpg", dpi=200)

../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/tests/test_agg.py:239: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/pyplot.py:722: in savefig
    res = fig.savefig(*args, **kwargs)
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/figure.py:2180: in savefig
    self.canvas.print_figure(fname, **kwargs)
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/backend_bases.py:2021: in print_figure
    canvas = self._get_output_canvas(format)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <matplotlib.backends.backend_agg.FigureCanvasAgg object at 0x7f51b8384520>
fmt = 'jpg'

    def _get_output_canvas(self, fmt):
        """
        Return a canvas suitable for saving figures to a specified file format.
    
        If necessary, this function will switch to a registered backend that
        supports the format.
        """
        # Return the current canvas if it supports the requested format.
        if hasattr(self, 'print_{}'.format(fmt)):
            return self
        # Return a default canvas for the requested format, if it exists.
        canvas_class = get_registered_canvas_class(fmt)
        if canvas_class:
            return self.switch_backends(canvas_class)
        # Else report error for unsupported format.
>       raise ValueError(
            "Format {!r} is not supported (supported formats: {})"
            .format(fmt, ", ".join(sorted(self.get_supported_filetypes()))))
E       ValueError: Format 'jpg' is not supported (supported formats: eps, pdf, pgf, png, ps, raw, rgba, svg, svgz)

../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/backend_bases.py:1961: ValueError
_______________________________ test_jpeg_alpha ________________________________
[gw1] linux -- Python 3.9.0 /usr/bin/python3

    def test_jpeg_alpha():
        Image = pytest.importorskip('PIL.Image')
    
        plt.figure(figsize=(1, 1), dpi=300)
        # Create an image that is all black, with a gradient from 0-1 in
        # the alpha channel from left to right.
        im = np.zeros((300, 300, 4), dtype=float)
        im[..., 3] = np.linspace(0.0, 1.0, 300)
    
        plt.figimage(im)
    
        buff = io.BytesIO()
        with rc_context({'savefig.facecolor': 'red'}):
>           plt.savefig(buff, transparent=True, format='jpg', dpi=300)

../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/tests/test_image.py:573: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/pyplot.py:722: in savefig
    res = fig.savefig(*args, **kwargs)
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/figure.py:2180: in savefig
    self.canvas.print_figure(fname, **kwargs)
../../BUILDROOT/python-matplotlib-3.1.2-1.fc32.x86_64/usr/lib64/python3.9/site-packages/matplotlib/backend_bases.py:2021: in print_figure
    canvas = self._get_output_canvas(format)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <matplotlib.backends.backend_agg.FigureCanvasAgg object at 0x7f9c07a06610>
fmt = 'jpg'

    def _get_output_canvas(self, fmt):
        """
        Return a canvas suitable for saving figures to a specified file format.
    
        If necessary, this function will switch to a registered backend that
        supports the format.
        """
        # Return the current canvas if it supports the requested format.
        if hasattr(self, 'print_{}'.format(fmt)):
            return self
        # Return a default canvas for the requested format, if it exists.
        canvas_class = get_registered_canvas_class(fmt)
        if canvas_class:
            return self.switch_backends(canvas_class)
        # Else report error for unsupported format.
>       raise ValueError(
            "Format {!r} is not supported (supported formats: {})"
            .format(fmt, ", ".join(sorted(self.get_supported_filetypes()))))
E       ValueError: Format 'jpg' is not supported (supported formats: eps, pdf, pgf, png, ps, raw, rgba, svg, svgz)

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01142555-python-matplotlib/

For all our attempts to build python-matplotlib with Python 3.9, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/package/python-matplotlib/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.9:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/

Let us know here if you have any questions.

Python 3.9 will be included in Fedora 33, but the initial bootstrapping has already started.
A build failure this early in the bootstrap sequence blocks us very much.