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Python – Conditional Prefix in List
• Last Updated : 01 Aug, 2020

Given a list of elements, attach different prefix according to condition.

Input : test_list = [45, 53, 76, 86, 3, 49], pref_1 = “LOSE-“, pref_2 = “WIN-”
Output : [‘LOSE-45’, ‘WIN-53’, ‘WIN-76’, ‘WIN-86’, ‘LOSE-3’, ‘LOSE-49’]
Explanation : All 50+ are prefixed as “WIN-” and others as “LOSE-“.

Input : test_list = [78, 53, 76, 86, 83, 69], pref_1 = “LOSE-“, pref_2 = “WIN-”
Output : [‘WIN-78’, ‘WIN-53’, ‘WIN-76’, ‘WIN-86’, ‘WIN-83’, ‘WIN-69’]
Explanation : All are 50+ hence prefixed “WIN-“.

Method #1 : Using loop

This brute way in which this task can be performed. In this, we perform the task of attatching the prefix by using conditionary operator and loop.

## Python3

 `# Python3 code to demonstrate working of ``# Conditional Prefix in List``# Using loop`` ` `# initializing list``test_list ``=` `[``45``, ``53``, ``76``, ``86``, ``3``, ``49``]`` ` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing pref 1``pref_1 ``=` `"LOW-"`` ` `# initializing pref 2``pref_2 ``=` `"HIGH-"`` ` `res ``=` `[]``for` `ele ``in` `test_list:``     ` `    ``# appending prefix on greater than 50 check``    ``if` `ele >``=` `50``:``        ``res.append(pref_2 ``+` `str``(ele))``    ``else` `:``        ``res.append(pref_1 ``+` `str``(ele))``         ` `# printing result ``print``(``"The prefixed elements : "` `+` `str``(res))`
Output
```The original list : [45, 53, 76, 86, 3, 49]
The prefixed elements : ['LOW-45', 'HIGH-53', 'HIGH-76', 'HIGH-86', 'LOW-3', 'LOW-49']
```

Method #2 : Using list comprehension

This is one of the ways in which this task can be performed. In this, we perform the similar task as above as one liner using list comprehension.

## Python3

 `# Python3 code to demonstrate working of ``# Conditional Prefix in List``# Using list comprehension`` ` `# initializing list``test_list ``=` `[``45``, ``53``, ``76``, ``86``, ``3``, ``49``]`` ` `# printing original list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing pref 1``pref_1 ``=` `"LOW-"`` ` `# initializing pref 2``pref_2 ``=` `"HIGH-"`` ` `# solution encapsulated as one-liner and conditional checks``res ``=` `[pref_2 ``+` `str``(ele) ``if` `ele >``=` `50` `else` `pref_1 ``+` `str``(ele) ``for` `ele ``in` `test_list]``         ` `# printing result ``print``(``"The prefixed elements : "` `+` `str``(res))`
Output
```The original list : [45, 53, 76, 86, 3, 49]
The prefixed elements : ['LOW-45', 'HIGH-53', 'HIGH-76', 'HIGH-86', 'LOW-3', 'LOW-49']
```

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