Why should I use operator.itemgetter(x) instead of [x]?

Question

There is a more general question here: In what situation should the built-in operator module be used in python?

The top answer claims that operator.itemgetter(x) is "neater" than, presumably, than lambda a: a[x]. I feel the opposite is true.

Are there any other benefits, like performance?

Answer 1

You shouldn't worry about performance unless your code is in a tight inner loop, and is actually a performance problem. Instead, use code that best expresses your intent. Some people like lambdas, some like itemgetter. Sometimes it's just a matter of taste.

itemgetter is more powerful, for example, if you need to get a number of elements at once. For example:

operator.itemgetter(1,3,5) 

is the same as:

lambda s: (s[1], s[3], s[5]) 

Answer 2

There are benefits in some situations, here is a good example.

>>> data = [('a',3),('b',2),('c',1)]
>>> from operator import itemgetter
>>> sorted(data, key=itemgetter(1))
[('c', 1), ('b', 2), ('a', 3)]

This use of itemgetter is great because it makes everything clear while also being faster as all operations are kept on the C side.

>>> sorted(data, key=lambda x:x[1])
[('c', 1), ('b', 2), ('a', 3)]

Using a lambda is not as clear, it is also slower and it is preferred not to use lambda unless you have to. Eg. list comprehensions are preferred over using map with a lambda.

Answer 3

Performance. It can make a big difference. In the right circumstances, you can get a bunch of stuff done at the C level by using itemgetter.

I think the claim of what is clearer really depends on which you use most often and would be very subjective