# Python | Truncate a list

Sometimes there is a requirement to restrict the list size to a particular number and remove all the elements from list which occur after a certain number as decided as list size. This is a useful utility for web development using Python. Let’s discuss certain ways in which this can be performed.

Method #1 : Using pop()
pop function can be repeated a number of times till size of the list reaches the threshold required as the size of the list. This uses a whole loop and hence is comparatively tedious.

 # Python3 code to demonstrate  # to truncate list using pop()    # initializing list   test_list = [1, 4, 5, 6, 7, 3, 8, 9, 10]    # printing original list print ("The original list is : " + str(test_list))    # size desired k = 5    # using pop() # to truncate list  n = len(test_list) for i in range(0, n - k ):     test_list.pop()    # printing result print ("The truncated list is : " +  str(test_list))

Output:

The original list is : [1, 4, 5, 6, 7, 3, 8, 9, 10]
The truncated list is : [1, 4, 5, 6, 7]

Method #2 : Using del + list slice
del operator can be used to delete all the elements that appear after the specific index, which is handled by the list slicing technique.

 # Python3 code to demonstrate  # to truncate list  # using del + list slicing    # initializing list   test_list = [1, 4, 5, 6, 7, 3, 8, 9, 10]    # printing original list print ("The original list is : " + str(test_list))    # size desired k = 5    # using del + list slicing # to truncate list  del test_list[5:]    # printing result print ("The truncated list is : " +  str(test_list))

Output:

The original list is : [1, 4, 5, 6, 7, 3, 8, 9, 10]
The truncated list is : [1, 4, 5, 6, 7]

Method #3 : Using list slicing
In this method, we just slice the first K elements and ignore all the elements that occur after K elements. This is most pythonic and recommended method to perform this task.

 # Python3 code to demonstrate  # to truncate list  # using list slicing    # initializing list   test_list = [1, 4, 5, 6, 7, 3, 8, 9, 10]    # printing original list print ("The original list is : " + str(test_list))    # size desired k = 5    # using list slicing # to truncate list  res = test_list[0 : 5]    # printing result print ("The truncated list is : " +  str(res))

Output:

The original list is : [1, 4, 5, 6, 7, 3, 8, 9, 10]
The truncated list is : [1, 4, 5, 6, 7]

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