itemgetter with default arguments

Fri May 4 11:17:14 EDT 2018

On Fri, May 4, 2018 at 7:01 AM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> Here are the specifications:
>> * you must use lambda, not def;

Why? This seems like an arbitrary constraint.
> * 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"

def itemgetter2(*items, default):
 return lambda seq: tuple(get_default(seq, item, default) for item in items)
def get_default(seq, item, default):
 try:
 return seq[item]
 except (IndexError, KeyError):
 return default
py> f = itemgetter2(1, 6, default="spam")
py> f("Hello World!")
('e', 'W')
py> f("Hello!")
('e', 'spam')