A re-occurring feature request is to add a default to itemgetter and
attrgetter. For example, we might say:
from operator import itemgetter
f = itemgetter(1, 6, default="spam") # proposed feature
f("Hello World!") # returns ('e', 'W')
f("Hello") # returns ('e', 'spam')
Two senior developers have rejected this feature, saying that we should
just use a lambda instead.
I might be slow today, but I cannot see how to write a clear, obvious,
efficient lambda that provides functionality equivalent to itemgetter
with a default value.
Putting aside the case where itemgetter takes multiple indexes, how about
the single index case? How could we get that functionality using a lambda
which is simple and obvious enough to use on the fly as needed, and
reasonably efficient?
Here are the specifications:
* you must use lambda, not def;
* the lambda must take a single function, the sequence you want to
extract an item from;
* you can hard-code the index in the body of the lambda;
* you can hard-code the default value in the body of the lambda;
* if sequence[index] exists, return that value;
* otherwise return the default value;
* it should support both positive and negative indices.
Example: given an index of 2 and a default of "spam":
(lambda seq: ... )("abcd") returns "c"
(lambda seq: ... )("") returns "spam"
I might be missing something horribly obvious, but I can't see how to do
this using a lambda. I tried using slicing:
seq[index:index+1]
which will return either an empty slice or a one-item slice, but that
didn't help me. I feel I'm missing something either obvious, or something
impossible, and I don't know which.
(This isn't a code-golf problem. I care more about being able to do it at
all, than about doing it in the minimum number of characters.)
--
Steve
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