mlflow log altair figure

mlflow log_figure only supports matplotlib or plotly. We can save an altair chart (or other library that saves .png) to a tempfile and use pillow Image to open the image, which is compatible with mlflow.log_image().

def save_altair_chart_to_mlflow(chart: alt.Chart, artifact_file: str) -> None:
	with tempfile.NamedTemporaryFile(suffix=".png", delete=False) as tmpfile:
		temp_filename = tmpfile.name
 
	try:
		chart.save(temp_filename)
		img = Image.open(temp_filename)
		mlflow.log_image(img, artifact_file)
 
	finally:
		# ensure the temporary file is removed
		os.unlink(temp_filename)