String loops in Python

Question

I have two pools of strings and I would like to do a loop over both. For example, if I want to put two labeled apples in one plate I'll write:

basket1 = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
    for fruit1 in basket1:

       basket2 = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
       for fruit2 in basket2:

            if fruit1 == fruit2:
                print 'Oops!'

            else:
                print "New Plate = %s and %s" % (fruit1, fruit2)

However, I don't want order to matter -- for example I am considering apple#1-apple#2 equivalent to apple#2-apple#1. What's the easiest way to code this?

I'm thinking about making a counter in the second loop to track the second basket and not starting from the point-zero in the second loop every time.

I don't see oranges in your above code.

roippi
– roippi

2013-11-01 15:30:03 +00:00
Commented Nov 1, 2013 at 15:30 — roippi
– roippi, Commented Nov 1, 2013 at 15:30
Sorry about that, I edited it!

Rotail
– Rotail

2013-11-01 15:31:49 +00:00
Commented Nov 1, 2013 at 15:31 — Rotail
– Rotail, Commented Nov 1, 2013 at 15:31

wrhall · Accepted Answer · 2013-11-01 15:50:20Z

3

If you change inequality (!=) to less than (<), and your lists (baskets) are sorted and the same, you won't get (b,a) once you have (a,b).

So

fruits = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
[(f1, f2) for f1 in fruits for f2 in fruits if f1 != f2]

becomes

fruits = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
[(f1, f2) for f1 in fruits for f2 in fruits if f1 < f2]

If, however, you have two distinct lists,

fruits1 = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
fruits2 = ['apple#1', 'apple#2', 'apple#3', 'apple#4', 'orange#1', 'orange#2']

You could still use the technique from above with a slight modification:

[(f1, f2) for f1 in fruits1 for f2 in fruits2 if f1 < f2]

edited Nov 1, 2013 at 15:50

wrhall

1,3081 gold badge12 silver badges26 bronze badges

answered Nov 1, 2013 at 15:35

Squidly

2,71719 silver badges44 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

wrhall Over a year ago

Nice solution -- you could generalize in case there are actually two different lists.

roippi · Accepted Answer · 2013-11-01 15:35:06Z

2

Easiest way is to just use itertools.combinations:

from itertools import combinations

for tup in combinations(basket1,2):
    print 'New Plate = {} and {}'.format(*tup)

New Plate = apple#1 and apple#2
New Plate = apple#1 and apple#3
New Plate = apple#1 and apple#4
New Plate = apple#2 and apple#3
New Plate = apple#2 and apple#4
New Plate = apple#3 and apple#4

answered Nov 1, 2013 at 15:35

roippi

26k4 gold badges52 silver badges75 bronze badges

1 Comment

DSM Over a year ago

No need to materialize the combinations with list().

Will Hunter · Accepted Answer · 2013-11-01 16:20:49Z

If, you have two distinct lists or you cannot compare with one fruit to another.

from itertools import product

basket1 = ['apple#1', 'apple#2', 'apple#3', 'apple#4']
basket2 = ['apple#3', 'apple#4', 'apple#5', 'apple#6']

result = []

for tup in product(basket1, basket2):
    if (tup[0] != tup[1]) and (set(tup) not in result):
        result.append(set(tup))
        print "New Plate = %s and %s" % (tup[0], tup[1])

New Plate = apple#1 and apple#3
New Plate = apple#1 and apple#4
New Plate = apple#1 and apple#5
New Plate = apple#1 and apple#6
New Plate = apple#2 and apple#3
New Plate = apple#2 and apple#4
New Plate = apple#2 and apple#5
New Plate = apple#2 and apple#6
New Plate = apple#3 and apple#4
New Plate = apple#3 and apple#5
New Plate = apple#3 and apple#6
New Plate = apple#4 and apple#5
New Plate = apple#4 and apple#6

Collectives™ on Stack Overflow

String loops in Python

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related