Python | Ways to merge strings into list

Given n strings, the task is to merge all strings into a single list. While developing an application, there come many scenarios when we need to operate on the string and convert it as some mutable data structure, say list. There are multiple ways we can convert strings into list based on the requirement. Let's understand it better with help of examples. 

Method #1: Using ast 

# Python code to merge all strings into a single list.

# Importing
import ast

# Initialization of strings
str1 ="'Geeks', 'for', 'Geeks'"
str2 ="'paras.j', 'jain.l'"
str3 ="'india'"


# Initialization of list
list = []

# Extending into single list
for x in (str1, str2, str3):
    list.extend(ast.literal_eval(x))

# printing output
print(list)

['Geeks', 'for', 'Geeks', 'paras.j', 'jain.l', 'i', 'n', 'd', 'i', 'a']

Time Complexity: O(n), where n is the length of the list
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list 

Method #2: Using eval 

# Python code to merge all strings into a single list.

# Initialization of strings
str1 ="['Geeks', 'for', 'Geeks']"
str2 ="['paras.j', 'jain.l']"
str3 ="['india']"


out = [str1, str2, str3]

out = eval('+'.join(out))

# printing output
print(out)

['Geeks', 'for', 'Geeks', 'paras.j', 'jain.l', 'india']

# Python code to merge all strings into a single list.

# Initialization of strings
str1 ="'Geeks', 'for', 'Geeks'"
str2 = "'121', '142'"
str3 ="'extend', 'India'"


out = [str1, str2, str3]

out = eval('+'.join(out))

# printing output
print(list(out))

['Geeks', 'for', 'Geeks121', '142extend', 'India']

Method #4: Using replace

#Initialization of strings
str1 = "'Geeks', 'for', 'Geeks'"
str2 = "'paras.j', 'jain.l'"
str3 = "'india'"

#Split each string by the comma character and remove the single quotes
list1 = [element.replace("'", "") for element in str1.split(",")]
list2 = [element.replace("'", "") for element in str2.split(",")]
list3 = [element.replace("'", "") for element in str3.split(",")]

#Merge the lists into a single list
merged_list = list1 + list2 + list3

#Print the merged list
print(merged_list)
#This code is contributed by Edula Vinay Kumar Reddy

['Geeks', ' for', ' Geeks', 'paras.j', ' jain.l', 'india']

The code above is defining three strings, each representing a list of strings separated by a comma. The lists are then split by the comma character and the single quotes are removed from each element. Finally, the lists are merged into a single list.

To split the strings, the split() method is used. This method takes a delimiter as input and returns a list of the elements in the string, separated by that delimiter.

To remove the single quotes from the elements, the replace() method is used. This method takes two arguments: the string to be replaced, and the string to replace it with. In this case, the single quotes are replaced with an empty string, effectively removing them from the element.

The lists are then merged using the + operator.

The time complexity of this code is O(n), where n is the total number of elements in the lists. This is because each element in the lists is processed only once. The space complexity is also O(n), since a new list is created which is the size of the sum of the original lists.

Method#5: Using loop and split.

Algorithm:

1. Initialize an empty list called "merged".
2. For each string in the input list "out":
   a. Remove the brackets from the string using string slicing (i.e. from index 1 to second last index).
   b. Split the resulting string at comma and store the resulting list of words in a variable called "words".
   c. Extend the "merged" list with the "words" list.
3. Print the "merged" list.

# Initialization of strings
str1 = "['Geeks', 'for', 'Geeks']"
str2 = "['paras.j', 'jain.l']"
str3 = "['india']"

out = [str1, str2, str3]

merged = []
for s in out:
    # Removing the brackets and splitting the string at comma
    words = s[1:-1].split(', ')
    merged.extend(words)

# Printing output
print(merged)
#this code contributed by tvsk

["'Geeks'", "'for'", "'Geeks'", "'paras.j'", "'jain.l'", "'india'"]

Time complexity: O(nm), where "n" is the length of the input list "out" and "m" is the maximum length of the individual strings in "out".
Auxiliary space complexity: O(nm), to store the "merged" list.

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