class - Summing Attribute in a list of Python Objects -

similar "what's concise way in python group , sum list of objects same property", have script in need sum attributes of list of objects. however, issue differs slightly.

i have class of objects attributes v, w, x, y, , z. need sum attribute z iterating through , matching attributes w, x, , y other w, x, , y attributes same. producing new summed value indexed w, x, , y.

here class objects:

class xb(object):     def __init__(self, v, w, x, y, z):        self.v = v        self.w = w        self.x = x        self.y = y        self.z = z  xbs = [xb()] 

my initial thought through series of nested if statements slows processing considerably , i'm sure logic out of whack.

for xb in xbs:     if xb.w == xb.w:           if xb.x == xb.x:               if xb.y == xb.y:                   sum(xb.z) 

any suggestions on appreciated!

you can using defaultdict:

from collections import defaultdict indexed_sums = defaultdict(int) o in xbs:     indexed_sums[(o.w, o.x, o.y)] += o.z 

for instance, if start (using class definition of xb):

xbs = [xb(1, 2, 3, 4, 5),        xb(1, 2, 3, 4, 5),        xb(1, 2, 3, 4, 5),        xb(1, 4, 3, 4, 5),        xb(1, 4, 3, 4, 3),        xb(1, 2, 3, 9, 3)] 

you end with:

print dict(indexed_sums) # {(4, 3, 4): 8, (2, 3, 4): 15, (2, 3, 9): 3} 

thus, sum w, x, y being 2, 3, 4 as:

indexed_sums[(2, 3, 4)] # 15 

---

note defaultdict doing little work here (it's dictionary of counts starts @ 0 default): main thing indexing (o.w, o.x, o.y) tuples in dictionary. have done same thing without defaultdict as:

indexed_sums = {} o in xbs:     if (o.w, o.x, o.y) not in indexed_sums:         indexed_sums[(o.w, o.x, o.y)] = 0     indexed_sums[(o.w, o.x, o.y)] += o.z 

the defaultdict saving 2 lines.