[Zope-dev] Stumped about handling this particular exception...

[skip@mojam.com (Skip Montanaro)]

I asked this question in a different form before but got only silence from
the list.  I'll give it another try...

I'm using ZServer and a snapshot of the Zope CVS directory.  When a user of
the web site fails to input a required form element, ZServer spits out

    Server Error: exceptions.ValueError, No input for required field<p>:
    file: /home/dolphin/skip/src/Zope/lib/python/ZPublisher/Converters.py line: 114

on the controlling terminal and the user sees

    Error response

    Error code 500. 

    Message: Internal Server Error. 

instead of a useful message that will help the user figure out what they did
wrong.  This makes them think my web site is broken, when it's actually
their input that's broken...

I've tried tracing the control flow back from Converters.py.  I manually
figured out the following call chain:

    HTTPRequest.py, line 246
    Publish.py, line 252

The three levels of try statement nesting in Publish.py made it unlikely
that I would figure out precisely what happens from the failed Request().  I
tried adding a little traceback printing to the field2required function:

    def field2required(v):
	if hasattr(v,'read'): v=v.read()
	else: v=str(v)
	if strip(v): return v
	try:
	    raise ValueError, 'No input for required field<p>'
	except:
	    import sys, traceback
	    ty, va, tb = sys.exc_info()
	    f = open("/tmp/traceback", "a")
	    f.write("\n\n---- %s, %s ----\n" % (ty, va))
	    traceback.print_tb(tb, None, f)
	    f.write("\n")
	    f.close()
	    raise

but all it dumps in /tmp/traceback is information for a single line:

    ---- exceptions.ValueError, No input for required field performers<p> ----
      File "/home/killer-whale/skip/src/Zope/lib/python/ZPublisher/Converters.py", line 115, in field2required
	raise ValueError, 'No input for required field %s<p>' % k

Any reason why it won't show me more of the execution stack?

I'm really flummoxed.  Any feedback on this problem would be much
appreciated.

Skip Montanaro	| Mojam: "Uniting the World of Music" http://www.mojam.com/
skip@mojam.com  | Musi-Cal: http://www.musi-cal.com/
518-372-5583