Dynamically serving a matplotlib image to the web using python

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You should

  • first write to a cStringIO object
  • then write the HTTP header
  • then write the content of the cStringIO to stdout

Thus, if an error in savefig occured, you could still return something else, even another header. Some errors won’t be recognized earlier, e.g., some problems with texts, too large image dimensions etc.

You need to tell savefig where to write the output. You can do:

format = "png"
sio = cStringIO.StringIO()
pyplot.savefig(sio, format=format)
print "Content-Type: image/%s\n" % format
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY) # Needed this on windows, IIS
sys.stdout.write(sio.getvalue())

If you want to embed the image into HTML: 

print "Content-Type: text/html\n"
print """<html><body>
...a bunch of text and html here...
<img src="data:image/png;base64,%s"/>
...more text and html...
</body></html>""" % sio.getvalue().encode("base64").strip()

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