Python | All occurrences of substring in string

Many times while working with strings, we have problems dealing with substrings. This may include the problem of finding all positions of a particular substrings in a string. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using list comprehension + startswith()
This task can be performed using the two functionalities. The startswith function primarily performs the task of getting the starting indices of substring and list comprehension is used to iterate through the whole target string.

# Python3 code to demonstrate working of 
# All occurrences of substring in string 
# Using list comprehension + startswith() 
  
# initializing string  
test_str = "GeeksforGeeks is best for Geeks"
  
# initializing substring 
test_sub = "Geeks"
  
# printing original string  
print("The original string is : " + test_str) 
  
# printing substring  
print("The substring to find : " + test_sub) 
  
# using list comprehension + startswith() 
# All occurrences of substring in string  
res = [i for i in range(len(test_str)) if test_str.startswith(test_sub, i)] 
  
# printing result  
print("The start indices of the substrings are : " + str(res)) 

Output :

The original string is : GeeksforGeeks is best for Geeks
The substring to find : Geeks
The start indices of the substrings are : [0, 8, 26]

Method #2 : Using re.finditer()
The finditer function of the regex library can help us perform the task of finding the occurrences of the substring in the target string and the start function can return the resultant index of each of them.

# Python3 code to demonstrate working of 
# All occurrences of substring in string 
# Using re.finditer() 
import re 
  
# initializing string  
test_str = "GeeksforGeeks is best for Geeks"
  
# initializing substring 
test_sub = "Geeks"
  
# printing original string  
print("The original string is : " + test_str) 
  
# printing substring  
print("The substring to find : " + test_sub) 
  
# using re.finditer() 
# All occurrences of substring in string  
res = [i.start() for i in re.finditer(test_sub, test_str)] 
  
# printing result  
print("The start indices of the substrings are : " + str(res)) 

Output :

The original string is : GeeksforGeeks is best for Geeks
The substring to find : Geeks
The start indices of the substrings are : [0, 8, 26]

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