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Python supports various looping techniques by certain inbuilt functions, in various sequential containers. These methods are primarily verya useful in competitive programming and also in various project which require a specific technique with loops maintaining the overall structure of code.

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Where they are used ?

Different looping techniques are primarily useful in the places where we don’t need to actually manipulate the structure and ordering of overall container, rather only print the elements for a single use instance, no inplace change occurs in the container. This can also be used in instances to save time.

Different looping techniques using Python data structures are:

  • Using enumerate():  enumerate() is used to loop through the containers printing the index number along with the value present in that particular index.
  • Using zip(): zip() is used to combine 2 similar containers(list-list or dict-dict) printing the values sequentially. The loop exists only till the smaller container ends. The detailed explanation of zip() and enumerate() can be found here.
  • Using iteritem(): iteritems() is used to loop through the dictionary printing the dictionary key-value pair sequentially.
  • Using items():  items() performs the similar task on dictionary as iteritems() but have certain disadvantages when compared with iteritems().
    • It is very time consuming. Calling it on large dictionaries consumes quite a lot of time.
    • It takes a lot of memory. Sometimes takes double the memory when called on dictionary.

python - Sample - python code :

# Python code to demonstrate working of iteritems(),items()
 
d = { "wikitechy" : "worlds best", "e-learning" : "website" }
 
# using iteritems to print the dictionary key-value pair
print ("The key value pair using iteritems is : ")
for i,j in d.iteritems():
    print i,j
     
# using items to print the dictionary key-value pair
print ("The key value pair using items is : ")
for i,j in d.items():
    print i,j

python tutorial - Output :

The key value pair using iteritems is : 
wikitechy worlds best
e-learning website
The key value pair using items is : 
wikitechy worlds best
e-learning website
  • Using sorted():  sorted() is used to print the container is sorted order. It doesn’t sort the container, but just prints the container in sorted order for 1 instance. Use of set() can be combined to remove duplicate occurrences.

python - Sample - python code :

# Python code to demonstrate working of sorted()
 
# initializing list
lis = [ 1 , 3, 5, 6, 2, 1, 3 ]
 
# using sorted() to print the list in sorted order
print ("The list in sorted order is : ")
for i in sorted(lis) :
    print (i,end=" ")
     
print ("\r")
     
# using sorted() and set() to print the list in sorted order
# use of set() removes duplicates.
print ("The list in sorted order (without duplicates) is : ")
for i in sorted(set(lis)) :
    print (i,end=" ")

python tutorial - Output :

The list in sorted order is : 
1 1 2 3 3 5 6 
The list in sorted order (without duplicates) is : 
1 2 3 5 6 
  • Using reversed(): reversed() is used to print the values of container in the descending order as declared.

python - Sample - python code :

# Python code to demonstrate working of reversed()
 
# initializing list
lis = [ 1 , 3, 5, 6, 2, 1, 3 ]
 
 
# using revered() to print the list in reversed order
print ("The list in reversed order is : ")
for i in reversed(lis) :
    print (i,end=" ")

python tutorial - Output :

The list in reversed order is : 
3 1 2 6 5 3 1 

Advantage of using above techniques over for, while loop

  • These techniques are quick to use and reduces coding effort. for, while loops needs the entire structure of container to be changed.
  • These Looping techniques  do not require any structural changes to container. They have keywords which present the exact purpose of usage. Whereas, no pre-predictions or guesses can be made in for, while loop i.e not easily understandable the purpose at a glance.
  • Looping technique make the code more concise than using for, while loopings.


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