[Python-Dev] operator.itemgetter with a callback method (original) (raw)

Alexandre Fiori fiorix at gmail.com
Sun Jan 11 17:02:17 CET 2009

hello

i was thinking about a possible improvement for the itemgetter the documentation page shows simple examples like sorting a dictionary by its integer values, like this:

inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)] getcount = itemgetter(1) map(getcount, inventory) [3, 2, 5, 1] sorted(inventory, key=getcount) [('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]

let's suppose i have dictionary where items are lists (instead of integers), and i want to sort it by the size of each list:

friends = { ... 'alex': ['bob', 'jane'], ... 'mary': ['steve', 'linda', 'foo bar'], ... 'john': ['max'] ... } sorted(friends.items(), key=itemgetter(1)) [('alex', ['bob', 'jane']), ('john', ['max']), ('mary', ['steve', 'linda', 'foo bar'])]

that doesn't work since itemgetter(1) will return a list, and that's not useful for sorting.

i didn't look at the code, but i suppose itemgetter is something like this:

class itemgetter: def init(self, index): self.index = index

def __call__(self, item):
    return tem[self.index]

in order for that sort (and possibly a lot of other things) to work properly, we could add a callback method for itemgetter, like this:

class itemgetter: def init(self, index, callback=None): self.index = index self.callback = callback

def __call__(self, item):
    return self.callback and self.callback(item[self.index]) or

item[self.index]

so, we could easly sort by the amount of data in each list, like this:

sorted(friends.items(), key=itemgetter(1, callback=len)) [('john', ['max']), ('alex', ['bob', 'jane']), ('foo', ['bar', 'steve', 'linda'])]

what do you guys think about it? please correct me if i'm wrong.

-- Ship ahoy! Hast seen the While Whale?

More information about the Python-Dev mailing list