Construct A Circular Loop In Python

I want to loop a list over a cycle. ex: I have three elements in the array L = [1,2,3] I want to get the output as L[0],L[1] L[1],L[2] L[2],L[0] Is there a easy way get the slight

Solution 1:

Using modulus operator

>>> a = [1,2,3]
>>> for x inrange(10):
        print a[x % len(a)]

Using itertools.cycle

>>> iterator = cycle(a)
>>> for _ inrange(10):
        printnext(iterator)

As for your output, you could just do this.

>>> for x inrange(10):
        print'{0}, {1}'.format(a[x % len(a)], a[(x+1) % len(a)])

>>> 1, 2>>> 2, 3>>> 3, 1... etc etc

Solution 2:

You can just use increasing index, and use modulo (remainder of division)

myList = [1,2,3]
for i in xrange(len(myList)):
    myTuple = (myList[i],myList[(i+1)%len(myList)])
    print myTuple

will produce:

(1,2)
(2,3)
(3,1)

Solution 3:

You could try something like

L = [1,2,3]
length = len(L)
for i in xrange(length):
        print L[i % length], L[(i+1) % length]

Output

1 2
2 3
3 1

This way, you can do something like xrange(10) and still have it cycle:

1 2
2 3
3 1
1 2
2 3
3 1
1 2
2 3
3 1
1 2

Solution 4:

l = [0,1,2,3]
for i in xrange(0, len(l)):
    print l[i], l[(i+1) % len(l)]


01122330

Solution 5:

There is a recipe in the itertools documentation that you can use:

import itertools
defpairwise(iterable):
    a, b = itertools.tee(iterable)
    next(b, None)
    return itertools.izip(a, b)

Call this with itertools.cycle(L) and you're good to go:

L = [1, 2, 3]
for pair in pairwise(itertools.cycle(L)):
    print pair
# (1, 2)# (2, 3)# (3, 1)# (1, 2)# ...