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# Python | Nth tuple index Subtraction by K

• Last Updated : 17 Dec, 2019

Many times, while working with records, we can have a problem in which we need to change the value of tuple elements. This is a common problem while working with tuples. Let’s discuss certain ways in which K can be subtracted to Nth element of tuple in list.

Method #1 : Using loop
Using loops this task can be performed. In this, we just iterate the list to change the Nth element by predefined value K in code.

 `# Python3 code to demonstrate working of``# Nth tuple element Subtraction by K``# Using loop`` ` `# Initializing list``test_list ``=` `[(``4``, ``5``, ``6``), (``7``, ``4``, ``2``), (``9``, ``10``, ``11``)]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Initializing N ``N ``=` `1`` ` `# Initializing K ``K ``=` `3`` ` `# Nth tuple element Subtraction by K``# Using loop``res ``=` `[]``for` `i ``in` `range``(``0``, ``len``(test_list)):``    ``res.append((test_list[i][``0``], test_list[i][N] ``-` `K, test_list[i][``2``]))`` ` `# printing result``print``(``"The tuple after removing K from Nth element : "` `+` `str``(res))`
Output :
```The original list is : [(4, 5, 6), (7, 4, 2), (9, 10, 11)]
The tuple after removing K from Nth element : [(4, 2, 6), (7, 1, 2), (9, 7, 11)]
```

Method #2 : Using list comprehension
This method is having the same approach as the above method, just reduces lines of code using list comprehension functionality to make code compact by size.

 `# Python3 code to demonstrate working of``# Nth tuple element Subtraction by K``# Using list comprehension`` ` `# Initializing list``test_list ``=` `[(``4``, ``5``, ``6``), (``7``, ``4``, ``2``), (``9``, ``10``, ``11``)]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Initializing N ``N ``=` `1`` ` `# Initializing K ``K ``=` `3`` ` `# Nth tuple element Subtraction by K``# Using list comprehension``res ``=` `[(a, b ``-` `K, c) ``for` `a, b, c ``in` `test_list]`` ` `# printing result``print``(``"The tuple after removing K from Nth element : "` `+` `str``(res))`
Output :
```The original list is : [(4, 5, 6), (7, 4, 2), (9, 10, 11)]
The tuple after removing K from Nth element : [(4, 2, 6), (7, 1, 2), (9, 7, 11)]
```

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