[Python-Dev] tally (and other accumulators) (original) (raw)

Georg Brandl g.brandl at gmx.net
Tue Apr 4 19:35:50 CEST 2006

Alex Martelli wrote:

On Apr 4, 2006, at 8:01 AM, Jeremy Hylton wrote:

On 4/4/06, Alex Martelli <aleaxit at gmail.com> wrote: import collections def tally(seq): d = collections.defaultdict(int) for item in seq: d[item] += 1 return dict(d) ... Putting it somewhere in collections seems like a great idea. defaultdict is a bit odd, because the functionality doesn't have anything to do with defaults, just dicts. maybe a classmethod on regular dicts would make more sense? Good points: it should probably be a classmethod on dict, or a function in module collections. I write this function regularly, so I'd be happy to have it available directly. Heh, same here -- soon as I saw it proposed on c.l.py I recognized an old friend and it struck me that, simple but widely used, it should be somewhere in the standard library.

Why not make it collections.bag, like the following:

class bag(dict): def init(self, iterable=None): dict.init(self) if iterable: self.update(iterable)

def update(self, iterable):
    for item in iterable:
        self.add(item)

def add(self, item):
    self[item] = self.get(item, 0) + 1

def remove(self, item):
    if self[item] == 1:
        del self[item]
    else:
        self[item] -= 1

def count(self, item):
    return self[item]

(etc.)

Georg

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