Update a list of tuples using another list in Python

When it is required to update a list of tuple using another list, the 'defaultdict' can be used.

Defaultdict is a container similar to dictionaries which is present in 'collections' module. It is a sub-class of the 'dict' class. It returns a dictionary-like object. The 'defaultdict' doesn't raise a KeyError ever. It provides a default value for the key which doesn't exist.

Below is a demonstration for the same −


Live Demo

from collections import defaultdict
def merge_vals(list_1, list_2):
   my_dict = defaultdict(list)
   for i, j in list_1 + list_2:
   return sorted([(i, max(j)) for i, j in my_dict.items()],
   key = lambda x:x[0])

my_list_1 = [('v', 1), ('q', 2), ('o', 0)]
my_list_2 = [('q', 5), ('o', 3)]

print("The first list of tuple is : ")
print("The second list of tuple is : ")
print("After merging, it becomes : ")
print(merge_vals(my_list_1, my_list_2))


The first list of tuple is :
[('v', 1), ('q', 2), ('o', 0)]
The second list of tuple is :
[('q', 5), ('o', 3)]
After merging, it becomes :
[('o', 3), ('q', 5), ('v', 1)]


  • The required libraries are imported.
  • A method named 'merge_vals' is defined, that takes two lists as arguments. A defaultdict is created.
  • The elements in the lists are iterated, and the element of the first list is taken as index, and the element from second index is appended to the dictionary.
  • This dictionary is sorted and returned.
  • Two lists of tuples are created, and displayed on the console.
  • The 'merge_vals' method is called by passing these two list of tuples as parameters.
  • This is displayed on the console as output.