I'm trying to save an Altair Chart in .png howether I get the error below. Could you please help me, I don't know what I'm doing wrong.
For information I manage to save the graph in .html and .json format, but nether .png, .jpeg, .svg aren't working. I already tried to insall altair_saver that returns me Requirement already satisfied.
Thank you for your help.
>>> plot.save('src/modality.png')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/app/installer/envPySpark/lib/python3.6/site-packages/altair/vegalite/v4/api.py", line 476, in save
result = save(**kwds)
File "/app/installer/envPySpark/lib/python3.6/site-packages/altair/utils/save.py", line 121, in save
**kwargs,
File "/app/installer/envPySpark/lib/python3.6/site-packages/altair/utils/mimebundle.py", line 60, in spec_to_mimebundle
return altair_saver.render(spec, format, mode=mode, **kwargs)
File "/app/installer/envPySpark/lib/python3.6/site-packages/altair_saver/_core.py", line 255, in render
Saver = _select_saver(method, mode=mode, fmt=fmt)
File "/app/installer/envPySpark/lib/python3.6/site-packages/altair_saver/_core.py", line 69, in _select_saver
raise ValueError(f"No enabled saver found that supports format={fmt!r}")
ValueError: No enabled saver found that supports format='png'
Update
After running this command line with my conda env
$ conda install -c conda-forge altair_saver
A new error appear :
>>> plot.save('src/modality.png')
TypeError: Cannot read property 'getContext' of null
at resize (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-scenegraph/build/vega-scenegraph.js:3377:26)
at CanvasRenderer.prototype$6.resize (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-scenegraph/build/vega-scenegraph.js:3427:5)
at CanvasRenderer.prototype$4.initialize (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-scenegraph/build/vega-scenegraph.js:2989:17)
at CanvasRenderer.prototype$6.initialize (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-scenegraph/build/vega-scenegraph.js:3422:28)
at initializeRenderer (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-view/build/vega-view.js:630:8)
at renderHeadless (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-view/build/vega-view.js:736:12)
at processTicksAndRejections (internal/process/task_queues.js:93:5)
at async View.renderToCanvas [as toCanvas] (/export/home/cgilles/.user_conda/miniconda/envs/metrologie/lib/vega-cli/node_modules/vega-view/build/vega-view.js:771:15)