[Zope-dev] BUG: ValueError while changing height of the template edit window

[Steve Alexander]

Guido van Rossum wrote:
> Can we get the same patch without the generic "except:", please?

<snipped part about whether there could be database corruption>

> int() happens to raise a bunch of different exceptions, and I think
> an unqualified except: clause is okay here (though it needs a
> comment).

I think this would be a useful note for the Zope3 style guide.


What exceptions can int() raise?

On converting a preexisting value to an int:

   ValueError, OverflowError, TypeError, AttributeError

   (Any others?)

On converting an instance that implements __int__:

   Anything at all.
   It can even return a non-int value.

On evaluating the expression inside the int() brackets:

   Anything at all.


I would suggest that only the four exceptions I listed first are worth 
catching. The other cases are programming errors.
Of those four exceptions, in this situation, I think you only need to 
catch ValueError. The other cases are application logic errors that I 
think it is counterproductive to catch. If you get one, there is a bug 
in some code, or some template, that should be fixed.


Here's how I produced the errors listed in the first category:

 >>> int('xxx')
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
ValueError: invalid literal for int(): xxx

 >>> import sys
 >>> int(sys.maxint+1)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
OverflowError: long int too large to convert to int

 >>> int(int)
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: int() argument must be a string or a number

 >>> int(AttributeError())
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
AttributeError: AttributeError instance has no attribute '__int__'

--
Steve Alexander