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Python | Pair iteration in list
  • Difficulty Level : Medium
  • Last Updated : 22 Jan, 2019

List iteration is common in programming, but sometimes one requires to print the elements in consecutive pairs. This particular problem is quite common and having a solution to it always turns out to be handy. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using list comprehension
List comprehension can be used to print the pairs by accessing current and next element in the list and then printing the same. Care has to be taken while pairing the last element with the first one to form a cyclic pair.




# Python3 code to demonstrate 
# pair iteration in list 
# using list comprehension
from itertools import compress
  
# initializing list  
test_list = [0, 1, 2, 3, 4, 5]
  
# printing original list
print ("The original list is : " + str(test_list))
  
# using list comprehension
# to perform pair iteration in list 
res = [((i), (i + 1) % len(test_list)) 
         for i in range(len(test_list))]
  
# printing result
print ("The pair list is : " + str(res))
Output:
The original list is : [0, 1, 2, 3, 4, 5]
The pair list is : [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 0)]

 
Method #2 : Using zip() + list slicing

zip function can be used to extract pairs over the list and slicing can be used to successively pair the current element with the next one for the efficient pairing.






# Python3 code to demonstrate 
# pair iteration in list 
# using zip() + list slicing 
from itertools import compress
  
# initializing list  
test_list = [0, 1, 2, 3, 4, 5]
  
# printing original list
print ("The original list is : " + str(test_list))
  
# using zip() + list slicing 
# to perform pair iteration in list 
res = list(zip(test_list, test_list[1:] + test_list[:1]))
  
# printing result
print ("The pair list is : " + str(res))
Output:
The original list is : [0, 1, 2, 3, 4, 5]
The pair list is : [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 0)]

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