Python CGI checklist: Difference between revisions
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"Internal server error" got you down... no problem, just check the following | "Internal server error" got you down... no problem, just check the following | ||
== | == Use extension ".cgi" == | ||
The default extension for CGI on a web server is .cgi. | |||
== She-Bang! == | == She-Bang! == | ||
The very first line of the file should be the "shebang" telling the system (Apache) how to run the script (in other words which language it is). | |||
<source lang="python"> | |||
#!/usr/bin/python | |||
</source> | |||
Even better, you could use the "env" trick (finds whatever python is available) + also specify a text encoding while you're at it (in case your code has special characters in it) | |||
<source lang="python"> | |||
#!/usr/bin/env python | |||
#-*- coding:utf-8 -*- | |||
</source> | |||
== chmod +x == | |||
Permissions must be set to "world-executable". You can maybe set this via an (s)ftp program, but the simplest / most failsafe way is directly via the shell: | |||
chmod +x myscript.cgi | chmod +x myscript.cgi | ||
| Line 35: | Line 30: | ||
chmod 755 myscript.cgi | chmod 755 myscript.cgi | ||
== | == Print the Content-type first! == | ||
The '''first output''' of your script must be the "HTTP headers", which at the very least should be a Content-type (with optional character set) '''followed by a blank line''' (which terminates the headers section). After that, all output is considered the "contents" of the document. | |||
<source lang="python"> | <source lang="python"> | ||
print "Content-type: text/html;charset=utf-8" | |||
print | |||
</source> | </source> | ||
== | == Troubleshooting == | ||
=== Make sure you are viewing the script through HTTP / a web server (and not as a local file) === | |||
It's the web server that actually performs a CGI script -- not the browser, so make sure you're looking at the script ''via a webserver'' rather than directly opening the script in your browser. (This would be one reason you might be seeing the raw source code of the script rather than it's output). In any case the URL (in the browser) should start with "http:" not "file:". | |||
http://localhost/cgi-bin/script.cgi | |||
http://pzwart3.wdka.hro.nl/~YOU/cgi-bin/script.cgi | |||
''not'' | |||
file:///this/can't/be/right/script.cgi | |||
See [[Serve.py]] for a tip on how to run a simple local CGI-capable webserver with a simple python command. | |||
=== Display python errors in the browser === | |||
Once the script is actually running, there might of course be something wrong in the code of the program itself. By default, if a python exception occurs, you will see either an Internal Server Error or (worse) a blank page. The ''cgitb'' module (CGI Trackback) will make python errors appear, and even formats them for a browser. | |||
<source lang="python"> | <source lang="python"> | ||
import cgitb; cgitb.enable() | |||
</source> | </source> | ||
== Check the webserver's error log == | === Check the webserver's error log === | ||
Use a shell on the server machine (so ssh to pzwart if that's where you're running) and: | |||
tail /var/log/ | tail /var/log/apache2/error.log | ||
Latest revision as of 11:34, 12 February 2014
"Internal server error" got you down... no problem, just check the following
Use extension ".cgi"
The default extension for CGI on a web server is .cgi.
She-Bang!
The very first line of the file should be the "shebang" telling the system (Apache) how to run the script (in other words which language it is).
#!/usr/bin/python
Even better, you could use the "env" trick (finds whatever python is available) + also specify a text encoding while you're at it (in case your code has special characters in it)
#!/usr/bin/env python
#-*- coding:utf-8 -*-
chmod +x
Permissions must be set to "world-executable". You can maybe set this via an (s)ftp program, but the simplest / most failsafe way is directly via the shell:
chmod +x myscript.cgi
or
chmod 755 myscript.cgi
Print the Content-type first!
The first output of your script must be the "HTTP headers", which at the very least should be a Content-type (with optional character set) followed by a blank line (which terminates the headers section). After that, all output is considered the "contents" of the document.
print "Content-type: text/html;charset=utf-8"
print
Troubleshooting
Make sure you are viewing the script through HTTP / a web server (and not as a local file)
It's the web server that actually performs a CGI script -- not the browser, so make sure you're looking at the script via a webserver rather than directly opening the script in your browser. (This would be one reason you might be seeing the raw source code of the script rather than it's output). In any case the URL (in the browser) should start with "http:" not "file:".
http://localhost/cgi-bin/script.cgi http://pzwart3.wdka.hro.nl/~YOU/cgi-bin/script.cgi
not
file:///this/can't/be/right/script.cgi
See Serve.py for a tip on how to run a simple local CGI-capable webserver with a simple python command.
Display python errors in the browser
Once the script is actually running, there might of course be something wrong in the code of the program itself. By default, if a python exception occurs, you will see either an Internal Server Error or (worse) a blank page. The cgitb module (CGI Trackback) will make python errors appear, and even formats them for a browser.
import cgitb; cgitb.enable()
Check the webserver's error log
Use a shell on the server machine (so ssh to pzwart if that's where you're running) and:
tail /var/log/apache2/error.log