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Turn "How to use Matplotlib in a web application server" into a sphinx-gallery example
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‎doc/faq/howto_faq.rst

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You may be able to work on separate figures from separate threads. However,
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you must in that case use a *non-interactive backend* (typically Agg), because
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most GUI backends *require* being run from the main thread as well.
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.. _howto-webapp:
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How to use Matplotlib in a web application server
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=================================================
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In general, the simplest solution when using Matplotlib in a web server is
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to completely avoid using pyplot (pyplot maintains references to the opened
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figures to make `~.matplotlib.pyplot.show` work, but this will cause memory
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leaks unless the figures are properly closed). Since Matplotlib 3.1, one
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can directly create figures using the `.Figure` constructor and save them to
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in-memory buffers. The following example uses Flask_, but other frameworks
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work similarly::
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import base64
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from io import BytesIO
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from flask import Flask
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from matplotlib.figure import Figure
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app = Flask(__name__)
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@app.route("/")
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def hello():
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# Generate the figure **without using pyplot**.
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fig = Figure()
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ax = fig.subplots()
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ax.plot([1, 2])
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# Save it to a temporary buffer.
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buf = BytesIO()
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fig.savefig(buf, format="png")
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# Embed the result in the html output.
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data = base64.b64encode(buf.getbuffer()).decode("ascii")
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return f"<img src='data:image/png;base64,{data}'/>"
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.. _Flask: http://flask.pocoo.org/
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When using Matplotlib versions older than 3.1, it is necessary to explicitly
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instantiate an Agg canvas; see e.g. :doc:`/gallery/user_interfaces/canvasagg`.
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.. _howto-click-maps:
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Clickable images for HTML
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-------------------------
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Andrew Dalke of `Dalke Scientific <http://www.dalkescientific.com>`_
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has written a nice `article
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<http://www.dalkescientific.com/writings/diary/archive/2005/04/24/interactive_html.html>`_
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on how to make html click maps with Matplotlib agg PNGs. We would
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also like to add this functionality to SVG. If you are interested in
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contributing to these efforts that would be great.

‎examples/user_interfaces/web_application_server_sgskip.py

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"""
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.. _howto-webapp:
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=================================================
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How to use Matplotlib in a web application server
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=================================================
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In general, the simplest solution when using Matplotlib in a web server is
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to completely avoid using pyplot (pyplot maintains references to the opened
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figures to make `~.matplotlib.pyplot.show` work, but this will cause memory
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leaks unless the figures are properly closed). Since Matplotlib 3.1, one
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can directly create figures using the `.Figure` constructor and save them to
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in-memory buffers. The following example uses Flask_, but other frameworks
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work similarly:
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.. _Flask: http://flask.pocoo.org/
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"""
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import base64
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from io import BytesIO
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from flask import Flask
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from matplotlib.figure import Figure
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app = Flask(__name__)
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@app.route("/")
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def hello():
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# Generate the figure **without using pyplot**.
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fig = Figure()
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ax = fig.subplots()
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ax.plot([1, 2])
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# Save it to a temporary buffer.
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buf = BytesIO()
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fig.savefig(buf, format="png")
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# Embed the result in the html output.
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data = base64.b64encode(buf.getbuffer()).decode("ascii")
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return f"<img src='data:image/png;base64,{data}'/>"
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# %%
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# When using Matplotlib versions older than 3.1, it is necessary to explicitly
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# instantiate an Agg canvas; see e.g. :doc:`/gallery/user_interfaces/canvasagg`.
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#
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# .. _howto-click-maps:
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#
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# Clickable images for HTML
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# -------------------------
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#
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# Andrew Dalke of `Dalke Scientific <http://www.dalkescientific.com>`_
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# has written a nice `article
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# <http://www.dalkescientific.com/writings/diary/archive/2005/04/24/interactive_html.html>`_
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# on how to make html click maps with Matplotlib agg PNGs. We would
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# also like to add this functionality to SVG. If you are interested in
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# contributing to these efforts that would be great.

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