unboundlocalerror with cgi module

[Kent Johnson]

Tim Hochberg wrote:
> Kent Johnson wrote:
>> David Bear wrote:
>>
>>> I'm attempting to use the cgi module with code like this:
>>>
>>> import cgi
>>> fo = cgi.FieldStorage()
>>> # form field names are in the form if 'name:part'
>>> keys = fo.keys()
>>> for i in keys:
>>>        try:
>>>                item,value=i.split(':')
>>>        except NameError, UnboundLocalError:
>>>                print "exception..."
>>>                item,value=(None,None)
>>> return(item,value)
>>>
>>> However, the except block does not seem to catch the exception and an
>>> unboundlocalerror is thrown anyway. What am I missing?
>>>        
>> I don't know why you would get an UnboundLocalError from the above code, 
>> but the correct syntax is
>>    except (NameError, UnboundLocalError):
> 
> One possibility is that there are no keys. Then the loop finishes 
> without ever setting item or values. This would give an unbound local 
> error. I assume that the OP would have noticed that in the traceback, 
> but perhaps he missed it.

I think that would be a NameError for the code shown because item and 
value are global variables. But anyway you raise a good point that 
perhaps the reason the exception is not being caught is because it is 
raised by code outside the scope of the try.

Also UnboundLocalError is a subclass of NameError so catching NameError 
should catch UnboundLocalError as well.

Kent