Add credit card string validator

strings/cc_validator.py

@@ -0,0 +1,68 @@
+def validate_initial_digits(credit_card_number: str) -> bool:
+    first_digit = int(credit_card_number[0])
+    if first_digit == 4 or first_digit == 5 or first_digit == 6:
+        return True
+    elif first_digit == 3:
+        second_digit = int(credit_card_number[1])
+        if second_digit == 7 or second_digit == 4 or second_digit == 5:
+            return True
+        else:
+            return False
+    return False
+
+
+def luhn_validation(credit_card_number: str) -> bool:
+    cc_number = credit_card_number
+    total = 0
+    half_len = len(cc_number) - 2
+    for i in range(half_len, -1, -2):
+        #  double the value of every second digit
+        digit = int(cc_number[i])
+        digit *= 2
+        # If doubling of a number results in a two digit number
+        # i.e greater than 9(e.g., 6 × 2 = 12),
+        # then add the digits of the product (e.g., 12: 1 + 2 = 3, 15: 1 + 5 = 6),
+        # to get a single digit number.
+        if digit > 9:
+            digit %= 10
+            digit += 1
+        cc_number = cc_number[:i] + str(digit) + cc_number[i + 1 :]
+        total += digit
+
+    # Sum up the remaining digits
+    for i in range(len(cc_number) - 1, -1, -2):
+        total += int(cc_number[i])
+
+    if total % 10 == 0:
+        return True
+
+    return False
+
+
+def validate_credit_card_number(number: str):
+    """
+    Function to validate the given credit card number
+    """
+    credit_card_number = str(number)
+    if credit_card_number.isdigit():
+        credit_card_number_length = len(credit_card_number)
+        if credit_card_number_length >= 13 and credit_card_number_length <= 16:
+            if validate_initial_digits(credit_card_number):
+                if luhn_validation(credit_card_number):
+                    print(f"Given number({number}) is Valid")
+                else:
+                    print(f"Invalid number({number}) given: Invalid Number")
+            else:
+                print(f"Invalid number({number}) given: Check starting number")
+        else:
+            print(f"Invalid number({number}) given: Check number length")
+    else:
+        print(
+            f"Invalid number({number}) given: Contains alphabets or special characters"
+        )
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()