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))
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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)
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OutputThe 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)
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OutputThe 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)
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OutputThe 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)
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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)
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OutputThe 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.