Using matplotlib in Python 3 CGI

Question

I've been trying to run matplotlib on CGI scripts with little success. I'm using Python3.5.

Most of the references I found online show functionality for Python2.x.

#!/usr/bin/python
import os,sys
import cgi
import cgitb
cgitb.enable()

import matplotlib
import matplotlib.pyplot as plt
import pylab

matplotlib.use('Agg')

plt.figure()
plt.plot([1,2,3])

import io
imgData = io.BytesIO()

pylab.savefig(imgData, format='png')

imgData.seek(0)

print("Content-type: image/png")
print()

print(imgData.read())

I am running Apache 2.4.18 on Arch Linux, and I get the following error:

The server encountered an internal error and was unable to complete your request.

Error message:
End of script output before headers: index.py

If you think this is a server error, please contact the webmaster.

My script has all required permissions to execute.

Any help will be appreciated.

UPDATE: I moved matplotlib.use('Agg') right beneath import matplotlib and now it gets past the server header error. The backend was getting declared earlier, hence the statement above has no effect. However, now I get the error:

The image 'http://localhost' cannot be displayed since it contains errors.

How can I correctly render images?

While you're absolutely correct, that doesn't seem to be the primary problem here since it isn't working even on changing it to 'image/png'. — doberoi96
– doberoi96, Commented Jan 12, 2016 at 11:58
Did you run this in a terminal? Instead of using print at the end, write the data to a file and then open it in the browser. See if that is okay. — jpcgt
– jpcgt, Commented Jan 12, 2016 at 14:42

doberoi96 · Accepted Answer · 2016-01-12 22:25:41Z

1

Solved my problem.

The following is working for me:

#!/usr/bin/python
import os,sys
import cgi
import cgitb
cgitb.enable()

import matplotlib
matplotlib.use('Agg')

os.environ['HOME'] = '/tmp'

import matplotlib.pyplot as plt

plt.plot([1,2,3])

print("Content-type: image/png")
print()

plt.savefig(sys.stdout, format='png')

answered Jan 12, 2016 at 22:25

doberoi96

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