added function to convert number to indian comma system

strings/indian_number_comma.py

@@ -0,0 +1,28 @@
+def indian_number_comma(number: str) -> str:
+    """
+    Returns the string with comma separated as per indian number system
+    :param number:
+    :return: number_with_comma
+    >>> indian_number_comma("6789")
+    6,789
+    >>> indian_number_comma("789")
+    789
+    >>> indian_number_comma("7980999")
+    79,80,999
+    """
+    last_3_digits = number[-3:]
+    # store the numbers before 3 digits
+    before_3 = number[:-3]
+    # converts the string into of 2-2 characters
+    split_list = [before_3[i : i + 2] for i in range(0, len(before_3), 2)]
+    # add the separated last digits to the list
+    split_list.append(last_3_digits)
+    # join the whole list around ,
+    result = ",".join(split_list)
+    return result
+
+
+if __name__ == "__main__":
+    assert indian_number_comma("6789"), "6,789"
+    assert indian_number_comma("789"), "789"
+    assert indian_number_comma("7980999"), "79,80,999"