itemgetter with default arguments

[Peter Otten]

Antoon Pardon wrote:

> On 05-05-18 09:33, Peter Otten wrote:
>> I think you have established that there is no straight-forward way to
>> write this as a lambda. But is adding a default to itemgetter the right
>> conclusion?
>>
>> If there were an exception-catching decorator you could write
>>
>> f = catch(IndexError, "spam")(itemgetter(2))
> 
> I think your catch function would be a usefull addition, but I don't see
> it solving this problem once we use itemgetter te get multiple entries.

Good catch()

;)

The obvious way, expressing the n-tuple case in terms of the solution for 
scalars

>>> f = lambda items: tuple(catch(IndexError, "spam")(itemgetter(i))(items) 
for i in (2, 1, 5))
>>> >>> f("abc")
('c', 'b', 'spam')

is a bit too complex to inline -- and also inefficient. You'd be tempted to 
factor out the repetetive parts

>>> f = lambda items, gets=[catch(IndexError, "spam")(itemgetter(i)) for i 
in (2, 1, 5)]: tuple(get(items) for get in gets)
>>> f("abc")
('c', 'b', 'spam')

and thus make it even less readable.

That said -- grepping my code I'm a bit surprised to find only

17 itemgetter(0)
 9 itemgetter(1)
 1 itemgetter(1, 0)
 1 itemgetter(*indices)

Checking /usr/lib/python3/dist-packages it looks like the situation is 
similar. I conclude that the most useful addition to the operator module 
would be

first = itemgetter(0)
second = itemgetter(1)