Added function to get nth occurrence of a string in another string.

text.py

@@ -111,5 +111,29 @@ def rsap(old: str, replace: str, position: int):
     return old[:position] + replace + old[position + 1:]
 
 
+def find_nth_occurrence(string: str, substring: str, n: int):
+    """
+    Find the nth occurrence of a substring in a string.
+    :param int n: 0 is the first occurrence
+    :return: -1 when the substring was not found, 0 is the first character.
+    """
+
+    if len(substring) == 1:  # make sure the replace string is not the substring (in rare cases, it might not work)
+        if substring == "a":
+            rep = "b"
+
+        else:
+            rep = "a"
+
+    else:
+        if not substring in "a" * len(substring):
+            rep = "a" * len(substring)
+
+        else:
+            rep = "b" * len(substring)
+
+    return string.replace(substring, rep, n - 1).find(substring)
+
+
 if __name__ == "__main__":
     example()