Python | Filter a list based on the given list of strings

Last Updated : 25 Jun, 2019

Given a List, the task is to filter elements from list based on another list of strings. These type of problems are quite common while scraping websites.

Examples:

Input:
List_string1 = ['key', 'keys', 'keyword', 'keychain', 'keynote']
List_string2 = ['home/key/1.pdf',
         'home/keys/2.pdf', 
         'home/keyword/3.pdf', 
         'home/keychain/4.pdf',
         'home/Desktop/5.pdf', 
         'home/keynote/6.pdf']
Output:
['home/Desktop/5.pdf']

Explanation: We filter only those element from 
list_string2 that do not have string in list_string1

Below are some ways to achieve the above task.

Method #1: Using Iteration

# Python code to  filter element from list  
# based on another list of string. 
  
# List Initialization 
Input = ['key', 'keys', 'keyword', 'keychain', 'keynote'] 
Input_string = ['home/key/1.pdf', 
         'home/keys/2.pdf',  
         'home/keyword/3.pdf',  
         'home/keychain/4.pdf', 
         'home/Desktop/5.pdf',  
         'home/keynote/6.pdf'] 
   
Output = Input_string.copy() 
temp = [] 
  
# Using iteration 
for elem in Input_string: 
    for n in Input: 
        if n in elem: 
            temp.append(elem) 
  
for elem in temp: 
    if elem in Output: 
        Output.remove(elem) 
  
# Printing 
print("List of keywords are:", Input) 
print("Given list:", Input_string) 
print("filtered list is :", Output) 

Output:

List of keywords are: [‘key’, ‘keys’, ‘keyword’, ‘keychain’, ‘keynote’]
Given list: [‘home/key/1.pdf’, ‘home/keys/2.pdf’, ‘home/keyword/3.pdf’, ‘home/keychain/4.pdf’, ‘home/Desktop/5.pdf’, ‘home/keynote/6.pdf’]
filtered list is : [‘home/Desktop/5.pdf’]

Method #2: Using list comprehension

# Python code to  filter element from list  
# based on another list of string. 
  
# List Initialization 
Input = ['key', 'keys', 'keyword', 'keychain', 'keynote'] 
Input_string = ['home/key/1.pdf', 
         'home/keys/2.pdf',  
         'home/keyword/3.pdf',  
         'home/keychain/4.pdf', 
         'home/Desktop/5.pdf',  
         'home/keynote/6.pdf'] 
  
# Using list comprehension 
Output = [b for b in Input_string if
          all(a not in b for a in Input)] 
  
# Printing 
print("List of keywords are:", Input) 
print("Given list:", Input_string) 
print("filtered list is :", Output) 

Output:

List of keywords are: [‘key’, ‘keys’, ‘keyword’, ‘keychain’, ‘keynote’]
Given list: [‘home/key/1.pdf’, ‘home/keys/2.pdf’, ‘home/keyword/3.pdf’, ‘home/keychain/4.pdf’, ‘home/Desktop/5.pdf’, ‘home/keynote/6.pdf’]
filtered list is : [‘home/Desktop/5.pdf’]

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