Python: Find the index of a given string at which a given substring starts

Last update on December 21 2024 07:47:01 (UTC/GMT +8 hours)

Index of substring or "Not found".

Write a Python program to determine the index of a given string at which a certain substring starts. If the substring is not found in the given string return 'Not found'.

Sample Solution:

Python Code:

# Function to find index of substring
def find_Index(str1, pos):
  # Check if pos longer than str1
  if len(pos) > len(str1):
    return 'Not found'
  # Iterate through str1
  for i in range(len(str1)):
    # Iterate through pos
    for j in range(len(pos)):
      # If match found, return index
      if str1[i + j] == pos[j] and j == len(pos) - 1:
        return i
      # Break if mismatch
      elif str1[i + j] != pos[j]:
        break
  return 'Not found'
# Test cases
print(find_Index("Python Exercises", "Ex"))
print(find_Index("Python Exercises", "yt"))
print(find_Index("Python Exercises", "PY"))

Sample Output:

7
1
Not found

Flowchart:

Python Code Editor:

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