Python | Prefix extraction depending on size

Last Updated : 26 Mar, 2020

Sometimes, while working with Python, we can have a problem in which we need to extract prefix from a string. This can be conditional sometimes, and we just need to extract specific length substring if size of string is larger than some N. Lets discuss certain ways in which this task can be performed.

Method #1 : Using loop
This is brute force way to perform this task, in which we extract the string according to size using a loop.

# Python3 code to demonstrate 
# Prefix extraction depending on size
# using loop
  
# Initializing list
test_list = ['geeksforgeeks', 'is', 'best', 'for', 'geeks']
  
# Initializing K 
K = 2
  
# Initializing N 
N = 4
  
# printing original list
print("The original list is : " + str(test_list))
  
# Prefix extraction depending on size
# using loop
res = []
for idx in test_list:
    if len(idx) >= N:
        res.append(idx[:K])
       
# printing result 
print ("List after prefix extraction : " + str(res))

Output :

The original list is : ['geeksforgeeks', 'is', 'best', 'for', 'geeks']
List after prefix extraction : ['ge', 'be', 'ge']

Method #2 : Using filter() + lambda
This task can also be performed using combination of above functions. In this, we perform the task of checking using filter(), and extraction is done in shorter way using list comprehension.

# Python3 code to demonstrate 
# Prefix extraction depending on size
# using filter() + lambda
  
# Initializing list
test_list = ['geeksforgeeks', 'is', 'best', 'for', 'geeks']
  
# Initializing K 
K = 2
  
# Initializing N 
N = 4
  
# printing original list
print("The original list is : " + str(test_list))
  
# Prefix extraction depending on size
# using filter() + lambda
res = [sub[:K] for sub in filter(lambda ele : len(ele) >= N, test_list)]
      
# printing result 
print ("List after prefix extraction : " + str(res))

Output :

The original list is : ['geeksforgeeks', 'is', 'best', 'for', 'geeks']
List after prefix extraction : ['ge', 'be', 'ge']

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Python | Prefix extraction depending on size