If PythonDebug is Off and an uncaught exception occurs in Python, the details of that exception will be logged in the Apache error log file. At the same time a 500 (HTTP_INTERNAL_SERVER_ERROR) response is returned to the client with whatever the configured default 500 error response message is for Apache.
If PythonDebug is On, the details are still logged to the error log, but the details of the exception will also be formatted and returned in the response to the client. In returning this response though, the HTTP status code is being returned as 200 (HTTP_OK) rather than the more correct 500 (HTTP_INTERNAL_SERVER_ERROR).
By wrongly returning 200 rather than 500, one could theoretically run up against problems like the response being cached, or if client was a non interactive application, it may think it was an entirely valid response and not flag in some way that it was actually an error.
The change to fix this in the code are as details in following patch. Note that returning 500 will still result in the message being displayed in a web browser, so for its intended purpose of displaying a traceback to a client, it will still work as required.
— lib/python/mod_python/apache.py (revision 396453)
+++ lib/python/mod_python/apache.py (working copy)
@@ -533,6 +533,7 @@
- write to client
+ req.status = HTTP_INTERNAL_SERVER_ERROR
req.content_type = 'text/html'
s = '\n<pre>\nMod_python error: "%s %s"\n\n' % (phase, hname)