221 views
Python | Ways to find nth Occurrence of Substring in a String
You can find the nth occurrence of a substring in a string in Python using various approaches, depending on your requirements and the complexity of the problem. Here are a few methods to achieve this:
Method 1: Using a Loop
Python
def find_nth_occurrence(input_string, substring, n):
start = input_string.find(substring)
while start >= 0 and n > 1:
start = input_string.find(substring, start + 1)
n -= 1
return start
input_string = "Python is a powerful programming language. Python is easy to learn."
substring = "Python"
n = 2
result = find_nth_occurrence(input_string, substring, n)
print(f"The {n}nd occurrence of '{substring}' starts at index {result}")Method 2: Using Regular Expressions
Python
import re
def find_nth_occurrence(input_string, substring, n):
pattern = re.compile(f"((?:.*?{re.escape(substring)}){{{n - 1}}}(.*?{re.escape(substring)}))")
match = pattern.search(input_string)
if match:
return match.start(2)
else:
return -1
input_string = "Python is a powerful programming language. Python is easy to learn."
substring = "Python"
n = 2
result = find_nth_occurrence(input_string, substring, n)
print(f"The {n}nd occurrence of '{substring}' starts at index {result}")Method 3: Using str.split()
Python
def find_nth_occurrence(input_string, substring, n):
parts = input_string.split(substring, n)
if len(parts) < n:
return -1
return len(input_string) - len(parts[-1]) - len(substring)
input_string = "Python is a powerful programming language. Python is easy to learn."
substring = "Python"
n = 2
result = find_nth_occurrence(input_string, substring, n)
print(f"The {n}nd occurrence of '{substring}' starts at index {result}")Method 4: Using a List Comprehension (Advanced)
Python
def find_nth_occurrence(input_string, substring, n):
indices = [i for i, c in enumerate(input_string) if input_string[i:i + len(substring)] == substring]
if len(indices) >= n:
return indices[n - 1]
return -1
input_string = "Python is a powerful programming language. Python is easy to learn."
substring = "Python"
n = 2
result = find_nth_occurrence(input_string, substring, n)
print(f"The {n}nd occurrence of '{substring}' starts at index {result}")Choose the method that best suits your needs and coding style. Method 1 and Method 2 are straightforward and recommended for most use cases.