Question

I want to maintain a list of strings and keep checking for different variables if they are in the list.

What I’m doing is :

li=[one,two,three]
for x in different_x_values:
  if(x in li):
    print 'yes'

Is there a faster way than using x in li that checks if a some string is in some other collection of strings?

Answer 1

I am sure you already got your answer, this is for the sake of completeness. Out of curiosity I ran the tests for the methods mentioned I got following results.

Size=size of main list
setopttime: the one that uses s1&s2
setintersectiontime: the one using intersection operation
bruteforcetime:burte force time

Size=1000
setoptime:0:00:00.001000
setintersectiontime:0:00:00.001000
bruteforcetime:0:00:00.005000

Size=10000
setoptime:0:00:00.001000
setintersectiontime:0:00:00.010000
bruteforcetime:0:00:00.367000

Size=100000
setoptime:0:00:00.001000
setintersectiontime:0:00:00.115000
bruteforcetime:0:00:35.444000

Method 1 (setopttime) wins hands down. Here is the code if you want to check.

import timeit
import datetime
def getList(size):
    s=[]
    for i in range(size):
        s.append(str(i))
    return s

def getSubList(size):
    s=[]
    for i in range(size/2):
        s.append(str(i))
    return s

def testSet(size):
    s=set(getList(size))
    sublist=set(getSubList(size))
    list(s&sublist)


def testIntersection(size):
    s=set(getList(size))
    sublist=set(getSubList(size))
    list(s.intersection(sublist))

def bruteForce(size):
    s=getList(size)
    sublist=getSubList(size)
    final=[]
    for elem in sublist:
        try:
            if s.index(elem)!=-1:
                final.append(elem)
        except ValueError:
            pass
currentsize=1000
for i in range(3):
    t1=datetime.datetime.now()
    testSet(1000)
    t2=datetime.datetime.now()
    testIntersection(currentsize)
    t3=datetime.datetime.now()
    bruteForce(currentsize)
    t4=datetime.datetime.now()
    print "Size="+str(currentsize)
    print "setoptime:"+str(t2-t1)
    print "setintersectiontime:"+str(t3-t2)
    print "bruteforcetime:"+str(t4-t3)
    currentsize=currentsize*10