Python - Conditional Prefix in List

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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