Python CGI

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Sample code

Hello World

print ("Content-type: text/html;charset=utf-8\n")
print ("Hello world!")

Dump the env!

#!/usr/bin/env python
#-*- coding:utf-8 -*-

import cgi

Receive some text from a form

#!/usr/bin/env python3
#-*- coding:utf-8 -*-

import cgitb; cgitb.enable()
import cgi

q = cgi.FieldStorage()
text = q.getvalue("text", "")
print ("Content-type: text/html;charset=utf-8\n")

# Print any received text in a purple box
print ("""<h1>Hello</h1>""")
if text:
    print ("""<div style="border: 5px solid purple">""")
    print (text)
    print ("""</div>""")

# Print the form
print ("""<form method="get" action="">
<textarea name="text"></textarea>
<input type="submit" />


Python has a CGI module that takes care of many things like working with values posted form a form or handling an uploaded file.

Python CGI Checklist

Python 3

Mini server

python3 -m http.server --cgi 8000

Unicode issue with Apache

An unfortunate side-effect of python3 getting "smarter" about text encoding is that it depends on the enclosing environment to "do the right thing", that is, pick the right text encoding to use when you print stuff. In Apache unfortunately the default cgi environment has no encoding set, so python defaults back to ASCII (and often makes your cgi silently fail in the browser). The solution is to make sure Apache passes on the "LANG" environment variable from the system to the script. This is achieved by two small steps:

  • Add PassEnv LANG to your site settings (sites-available/000-default.conf inside the <VirtualHost> or to the end of your /etc/apache2/apache2.conf or .htaccess).
  • Uncomment . /etc/default/locale line in /etc/apache2/envvars.

Finally: make sure line similar to LANG="en_US.UTF-8" is present in /etc/default/locale (if it's not, you may need to reconfigure your shell environment to use utf-8).

A simple test CGI...

#!/usr/bin/env python3
import sys
import cgitb; cgitb.enable()

print('Content-Type: text/html; charset=utf-8')
print('<html><body><pre>' + sys.stdout.encoding + '</pre>h€lló wörld<body></html>')