Create List Of Object Attributes In Python

I have a list of objects: [Object_1, Object_2, Object_3] Each object has an attribute: time: Object_1.time = 20 Object_2.time = 30 Object_3.time = 40 I want to create a list of t

Solution 1:

List comprehension is what you're after:

list_of_objects = [Object_1, Object_2, Object_3]
[x.time for x in list_of_objects]

Solution 2:

from operator import attrgetter
items = map(attrgetter('time'), objects)

Solution 3:

The fastest (and easiest to understand) is with a list comprehension.

See the timing:

import timeit
import random
c=10000classSomeObj:
    def__init__(self, i):
        self.attr=i

defloopCR():
    l=[]
    for i inrange(c):
        l.append(SomeObj(random.random()))

    return l 

defcompCR():
    return [SomeObj(random.random()) for i inrange(c)]   

defloopAc():
    lAttr=[]
    for e in l:
        lAttr.append(e.attr)

    return lAttr

defcompAc():
    return [e.attr for e in l]             

t1=timeit.Timer(loopCR).timeit(10)
t2=timeit.Timer(compCR).timeit(10)
print"loop create:", t1,"secs"print"comprehension create:", t2,"secs"print'Faster of those is', 100.0*abs(t1-t2) / max(t1,t2), '% faster'print 

l=compCR()

t1=timeit.Timer(loopAc).timeit(10)
t2=timeit.Timer(compAc).timeit(10)
print"loop access:", t1,"secs"print"comprehension access:", t2,"secs"print'Faster of those is', 100.0*abs(t1-t2) / max(t1,t2), '% faster'

Prints:

loop create: 0.103852987289 secs
comprehension create: 0.0848100185394 secs
Faster of those is18.3364670069 % faster

loop access: 0.0206878185272 secs
comprehension access: 0.00913000106812 secs
Faster of those is55.8677438315 % faster

So list comprehension is both faster to write and faster to execute.