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# Python – Tuple key detection from value list

• Last Updated : 12 Mar, 2020

Sometimes, while working with record data, we can have a problem in which we need to extract the key which has matching value of K from its value list. This kind of problem can occur in domains that are linked to data. Lets discuss certain ways in which this task can be performed.

Method #1 : Using List comprehension
This task can be performed using List comprehension. In this, we iterate through each records and test it’s value list for K. If found we return that key.

 `# Python3 code to demonstrate ``# Tuple key detection from value list``# using List comprehension`` ` `# Initializing list``test_list ``=` `[(``'Gfg'``, [``1``, ``3``, ``4``]), (``'is'``, [``5``, ``8``, ``10``]), (``'best'``, [``11``, ``9``, ``2``])]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Initializing K ``K ``=` `4`` ` `# Tuple key detection from value list``# using List comprehension``res ``=` `[sub[``0``] ``for` `sub ``in` `test_list ``if` `K ``in` `sub[``1``]]``             ` `# printing result ``print` `(``"The required key of list values : "` `+` `str``(res))`
Output :
```The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The required key of list values : ['Gfg']
```

Method #2 : Using `filter()` + lambda
The combination of above functions can also be used to perform this task. In this, filter() is used to check for existance in list and extract the required key with help of lambda.

 `# Python3 code to demonstrate ``# Tuple key detection from value list``# using filter() + lambda`` ` `# Initializing list``test_list ``=` `[(``'Gfg'``, [``1``, ``3``, ``4``]), (``'is'``, [``5``, ``8``, ``10``]), (``'best'``, [``11``, ``9``, ``2``])]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Initializing K ``K ``=` `4`` ` `# Tuple key detection from value list``# using filter() + lambda``res ``=` `list``(``filter``(``lambda` `sub, ele ``=` `K : ele ``in` `sub[``1``], test_list))``             ` `# printing result ``print` `(``"The required key of list values : "` `+` `str``(res[``0``][``0``]))`
Output :
```The original list is : [('Gfg', [1, 3, 4]), ('is', [5, 8, 10]), ('best', [11, 9, 2])]
The required key of list values : Gfg
```

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