Python | Append suffix/prefix to strings in list (original) (raw)

Last Updated : 03 May, 2023

Sometimes, while working with Python, we can a problem in which we need to pad strings in lists at trailing or leading position. This kind of problem is quite common and can occur in day-day programming or web development. Let’s discuss a way in which this task can be performed.

Method #1: Using + operator + list comprehension In this task, we just append the string at rear or front position using + operator and list comprehension is used to iterate through all the elements.

Python3

test_list = [ 'a' , 'b' , 'c' , 'd' ]

print ( "The original list : " + str (test_list))

append_str = 'gfg'

pre_res = [append_str + sub for sub in test_list]

suf_res = [sub + append_str for sub in test_list]

print ( "list after prefix addition : " + str (pre_res))

print ( "list after suffix addition : " + str (suf_res))

Output :

The original list : ['a', 'b', 'c', 'd'] list after prefix addition : ['gfga', 'gfgb', 'gfgc', 'gfgd'] list after suffix addition : ['agfg', 'bgfg', 'cgfg', 'dgfg']

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #2: Using itertools.starmap(): The python library itertools provides a function called “starmap()” which can be used to apply the same function to multiple inputs from an iterable, in this case, it can be used to append the suffix/prefix to each string in the list, this approach would have a time complexity of O(n) and auxiliary space of O(n) as well.

Python3

import itertools

test_list = [ 'a' , 'b' , 'c' , 'd' ]

print ( "The original list :" , test_list)

append_str = 'gfg'

pre_res = list (itertools.starmap( lambda s: append_str + s, test_list))

suf_res = list (itertools.starmap( lambda s: s + append_str, test_list))

print ( "list after prefix addition :" , pre_res)

print ( "list after suffix addition :" , suf_res)

Output

The original list : ['a', 'b', 'c', 'd'] list after prefix addition : ['gfga', 'gfgb', 'gfgc', 'gfgd'] list after suffix addition : ['agfg', 'bgfg', 'cgfg', 'dgfg']

Method #3: Using map and lambda functions

Python3

def add_prefix_suffix(lst, prefix, suffix):

`` pre_res = list ( map ( lambda x: prefix + x, lst))

`` suf_res = list ( map ( lambda x: x + suffix, lst))

`` return pre_res, suf_res

test_list = [ 'a' , 'b' , 'c' , 'd' ]

print ( "The original list :" , test_list)

pre_res, suf_res = add_prefix_suffix(test_list, 'gfg' , 'gfg' )

print ( "list after prefix addition :" , pre_res)

print ( "list after suffix addition :" , suf_res)

Output

The original list : ['a', 'b', 'c', 'd'] list after prefix addition : ['gfga', 'gfgb', 'gfgc', 'gfgd'] list after suffix addition : ['agfg', 'bgfg', 'cgfg', 'dgfg']

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #4: Using For loop.

Python3

test_list = [ 'a' , 'b' , 'c' , 'd' ]

prefix,suffix = 'gfg' , 'gfg'

print ( "The original list :" , test_list)

pre_res = []

suf_res = []

for item in test_list:

`` pre_res.append(prefix + item)

`` suf_res.append(item + suffix)

print ( "list after prefix addition :" , pre_res)

print ( "list after suffix addition :" , suf_res)

Output

The original list : ['a', 'b', 'c', 'd'] list after prefix addition : ['gfga', 'gfgb', 'gfgc', 'gfgd'] list after suffix addition : ['agfg', 'bgfg', 'cgfg', 'dgfg']

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #5: Using numpy module:

Step-by-step approach:

• Initialize an empty list to store the result of prefix addition and another empty list to store the result of suffix addition.
• Iterate through the original list, and for each element, append the prefix to the beginning of the element and append the result to the prefix addition list.
• Similarly, append the suffix to the end of the element and append the result to the suffix addition list.
• Print the original list, prefix addition list, and suffix addition list.

Python3

import numpy as np

test_list = [ 'a' , 'b' , 'c' , 'd' ]

prefix,suffix = 'gfg' , 'gfg'

pre_res = np.char.add(prefix, test_list)

suf_res = np.char.add(test_list, suffix)

print ( "The original list :" , test_list)

print ( "list after prefix addition :" , pre_res)

print ( "list after suffix addition :" , suf_res)

Output:

The original list : ['a', 'b', 'c', 'd'] list after prefix addition : ['gfga' 'gfgb' 'gfgc' 'gfgd'] list after suffix addition : ['agfg' 'bgfg' 'cgfg' 'dgfg']

Time complexity: O(n), where n is the number of elements in the input list. This is because we iterate through each element once to perform the prefix and suffix addition.
Auxiliary Space: O(n), where n is the number of elements in the input list. This is because we create two lists of size n to store the results of the prefix and suffix addition

Method #6: Using the reduce() function from the functools module

Step-by-step approach:

• Import the reduce() function from the functools module.
• Create a test_list of strings.
• Create two variables prefix and suffix with the desired string values.
• Use the reduce() function with a lambda expression to iterate through each element item in test_list, concatenate prefix to it, and append the result to pre_res.
• Use the reduce() function with a lambda expression to iterate through each element item in test_list, concatenate suffix to it, and append the result to suf_res.
• Print the original list, test_list, the list after prefix addition, pre_res, and the list after suffix addition, suf_res.

Python3

from functools import reduce

test_list = [ 'a' , 'b' , 'c' , 'd' ]

prefix, suffix = 'gfg' , 'gfg'

pre_res = reduce ( lambda res, item: res + [prefix + item], test_list, [])

suf_res = reduce ( lambda res, item: res + [item + suffix], test_list, [])

print ( "The original list :" , test_list)

print ( "List after prefix addition :" , pre_res)

print ( "List after suffix addition :" , suf_res)

Output

The original list : ['a', 'b', 'c', 'd'] List after prefix addition : ['gfga', 'gfgb', 'gfgc', 'gfgd'] List after suffix addition : ['agfg', 'bgfg', 'cgfg', 'dgfg']

Time complexity: O(n), where n is the length of test_list.
Auxiliary space: O(n), where n is the length of test_list.