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Python – Find the sum of Length of Strings at given indices
  • Last Updated : 02 Dec, 2020

Given the String list, write a Python program to compute sum of lengths of custom indices of list.

Examples:

Input : test_list = [“gfg”, “is”, “best”, “for”, “geeks”], idx_list = [0, 1, 4] 
Output : 10 
Explanation : 3 + 2 + 5 = 10. (Sizes of strings at idx.)
 

Input : test_list = [“gfg”, “is”, “best”, “for”, “geeks”], idx_list = [0, 2, 4] 
Output : 12 
Explanation : 3 + 4 + 5 = 12. 

Method #1 : Using len() + loop 



In this, we iterate for all indices and check if they occur in index list, if yes, increment frequency in summation counter.

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# Python3 code to demonstrate working of
# Length sum of custom indices Strings
# Using len() + loop
  
# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]
  
# printing original lists
print("The original list is : " + str(test_list))
  
# initializing idx list
idx_list = [0, 1, 4]
  
res = 0
for idx, ele in enumerate(test_list):
  
    # adding length if index in idx_list
    if idx in idx_list:
        res += len(ele)
  
# printing result
print("Computed Strings lengths sum : " + str(res))

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Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Computed Strings lengths sum : 10

Method #2 : Using sum() + len() + list comprehension

In this, we perform task of performing summation using sum(), rest all the functionalities are performed as per above method, just as one-liner.

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# Python3 code to demonstrate working of
# Length sum of custom indices Strings
# Using sum() + len() + list comprehension
  
# initializing list
test_list = ["gfg", "is", "best", "for", "geeks"]
  
# printing original lists
print("The original list is : " + str(test_list))
  
# initializing idx list
idx_list = [0, 1, 4]
  
# performing summation using sum()
# len() used to get strings lengths
res = sum([len(ele) for idx, ele in enumerate(test_list) if idx in idx_list])
  
# printing result
print("Computed Strings lengths sum : " + str(res))

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Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeks']
Computed Strings lengths sum : 10

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