Python | Extract length of longest string in list

Sometimes, while working with a lot of data, we can have a problem in which we need to extract the maximum length of all the strings in list. This kind of problem can have application in many domains. Let’s discuss certain ways in which this task can be performed. 

Method #1 : Using max() + generator expression, The combination of above functionalities can be used to perform this task. In this, we extract all the list lengths using generator expression and return maximum of them using max(). 

Python3

# Python3 code to demonstrate working of
# Extracting length of longest string in list
# using max() + generator expression

# initialize list
test_list = ['gfg', 'is', 'best']

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

# Extracting length of longest string in list
# using max() + generator expression
res = max(len(ele) for ele in test_list)

# printing result
print("Length of maximum string is : " + str(res))

Output : 

The original list : ['gfg', 'is', 'best']
Length of maximum string is : 4

Time Complexity: O(n), where n is the length of the input list. This is because we’re using max() + generator expression which has a time complexity of O(n) in the worst case.
Auxiliary Space: O(1), as we’re using constant additional space.

Method #2 : Using len() + key argument + max() The combination of above functions can be used to perform this task. In this, we extract the maximum length using len() and max(). It is faster than above method as it performs more task built in rather than overhead by generator expression. 

Python3

# Python3 code to demonstrate working of
# Extracting length of longest string in list
# using len() + key argument + max()

# initialize list
test_list = ['gfg', 'is', 'best']

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

# Extracting length of longest string in list
# using len() + key argument + max()
res = len(max(test_list, key = len))

# printing result
print("Length of maximum string is : " + str(res))

Output : 

The original list : ['gfg', 'is', 'best']
Length of maximum string is : 4

Time Complexity: O(n), where n is the length of the list test_list 
Auxiliary Space: O(1) constant additional space required

Method 3: Alternative method

Python3

lst=['gfg', 'is', 'best']
max_length,longest_element = max([(len(x),x) for x in (lst)])
print("max length is: ",max_length)
print("longest string is: ", longest_element)

Output

max length is:  4
longest string is:  best

Method 4: Using the enumerate function

Python3

lst=['gfg', 'is', 'best']
max_length,longest_element = max([(len(x),x) for a,x in enumerate(lst)])
print("max length is: ",max_length)
print("longest string is: ", longest_element)

Output

max length is:  4
longest string is:  best

Method 5: Using the reduce function

One unique approach to extract the maximum length of all strings in a list is using the built-in function “reduce” from the “functools” module. The reduce function applies a function cumulatively to the elements of an iterable and returns a single output. In this case, we can use the function “max” as the cumulative function and the iterable is a list of the lengths of each string in the original list.

Here is an example of how to use the reduce function to extract the maximum length of all strings in a list:

Python3

from functools import reduce

# initialize list
test_list = ['gfg', 'is', 'best']

# Extracting length of longest string in list using reduce function
res = reduce(lambda x, y: max(x, y), map(len, test_list))

# printing result
print("Length of maximum string is : " + str(res))
#this code is contributed by edula vinay kumar reddy

Output

Length of maximum string is : 4

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

Method 6: Using the list comprehension:

Python3

# Initialize the list of strings
test_list = ['gfg', 'is', 'best']

# Use a list comprehension to calculate the length of each string
# in the list and store the results in a new list
string_lengths = [len(i) for i in test_list]

# Find the maximum length from the list of string lengths
max_length = max(string_lengths)

# Print the result
print("Length of maximum string is :", max_length)

Output

Length of maximum string is : 4

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