Terry Reedy wrote:
On 7/31/2012 4:49 PM, Chris Kaynor wrote:
On Tue, Jul 31, 2012 at 1:21 PM, Terry Reedy wrote:
Another example: KeyError and IndexError are both subscript errors,
but there is no SubscriptError superclass, even though both work
thru the same mechanism -- __getitem__. The reason is that there is
no need for one. In 'x[y]', x is usually intented to be either a
sequence or mapping, but not possibly both. In the rare cases when
one wants to catch both errors, one can easily enough. To continue
the example above, popping an empty list and empty set produce
IndexError and KeyError respectively:
try:
while True:
process(pop())
except (KeyError, IndexError):
pass # empty collection means we are done
There is a base type for KeyError and IndexError: LookupError.
http://docs.python.org/library/exceptions.html#exception-hierarchy
Oh, so there is. Added in 1.5 strictly as a never-directly-raised base
class for the above pair, now also directly raised in codecs.lookup. I
have not decided if I want to replace the tuple in the code in my book.
I think I'd stick with the tuple -- LookupError could just as easily
encompass NameError and AttributeError.
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