Using a while loop over lists in Python

Question

So I have a need to have a while loop that runs so long as the maximum value from list1 is greater than the minimum value from list2. Right now, I have this:

    count=0
    list1= mine
    list2= friend
    while max(list1)>min(list2):
        count+=1
        list1= list1.remove(max(list1))
        list2= list2.remove(min(list2))
    return count

However, the function cannot be called because it says the object is non-iterable. Can someone please tell me how to fix this?

Thank you so very much

lejlot · Accepted Answer · 2013-10-21 21:22:22Z

2

list.remove does not return the list, so once you remove the first value, you assign to the list1 and list2 variables non iterable objects, simply change

list1= list1.remove(max(list1))
list2= list2.remove(min(list2))

to

list1.remove(max(list1))
list2.remove(min(list2))

answered Oct 21, 2013 at 21:22

lejlot

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Comments

Andrew Clark · Accepted Answer · 2013-10-21 21:22:54Z

2

list.remove() modifies the list in place and returns None, so after the first iteration both list1 and list2 will be None. Just remove the assignment from your remove lines:

while max(list1)>min(list2):
    count+=1
    list1.remove(max(list1))
    list2.remove(min(list2))

answered Oct 21, 2013 at 21:22

Andrew Clark

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Comments

alko · Accepted Answer · 2013-10-21 21:56:58Z

Problem is, list.remove returns None. While you can easely solve this by replacing list1=list1.remove(...), may I propose you other solution which

do not modify list1, list2, since this can lead to a buggy code;
is a bit faster, since list.remove is not very effective

Suggested code:

import timeit
from itertools import izip_longest

def via_remove(l1, l2):
    count = 1
    while max(l1)>min(l2):
        count+=1
        l1.remove(max(l1))
        l2.remove(min(l2))
    return count

def with_itertools(l1, l2):
    c = 1
    for l1_max, l2_min in izip_longest(sorted(l1, reverse=True), sorted(l2)):
        if l1_max <= l2_min:
            break
        c += 1
    return c

print timeit.timeit('from __main__ import via_remove; via_remove(range(1000), range(1000))', number=100)
7.82893552113

print timeit.timeit('from __main__ import with_itertools; with_itertools(range(1000), range(1000))', number=100)
0.0196773612289

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