Add credit card string validator

strings/credit_card_validator.py

@@ -0,0 +1,97 @@
+def validate_initial_digits(credit_card_number: str) -> bool:
+    """
+    Function to validate initial digits of a given credit card number.
+    >>> valid = "4111111111111111 41111111111111 34 35 37 412345 523456 634567"
+    >>> all(validate_initial_digits(cc) for cc in valid.split())
+    True
+    >>> invalid = "32323 36111111111111"
+     >>> all(validate_initial_digits(cc) is False for cc in invalid.split())
+    True
+    """
+    first_digit = int(credit_card_number[0])
+    if first_digit in (4, 5, 6):
+        return True
+    elif first_digit == 3:
+        second_digit = int(credit_card_number[1])
+        return second_digit in (4, 5, 7)
+
+    return False
+
+
+def luhn_validation(credit_card_number: str) -> bool:
+    """
+    Function to luhn algorithm validation for a given credit card number.
+    >>> luhn_validation('4111111111111111')
+    True
+    >>> luhn_validation('36111111111111')
+    True
+    >>> luhn_validation('41111111111111')
+    False
+    """
+    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])
+
+    return total % 10 == 0
+
+
+def validate_credit_card_number(number: str) -> bool:
+    """
+    Function to validate the given credit card number.
+    >>> validate_credit_card_number('4111111111111111')
+    Given number(4111111111111111) is Valid
+    >>> validate_credit_card_number('helloworld$')
+    Invalid number(helloworld$) given: Contains alphabets or special characters
+    >>> validate_credit_card_number('32323')
+    Invalid number(32323) given: Check number length
+    >>> validate_credit_card_number('32323323233232332323')
+    Invalid number(32323323233232332323) given: Check number length
+    >>> validate_credit_card_number('36111111111111')
+    Invalid number(36111111111111) given: Check starting number
+    >>> validate_credit_card_number('41111111111111')
+    Invalid number(41111111111111) given: Invalid Number
+    """
+    error_message = f"Invalid number({number}) given: "
+    credit_card_number = str(number)
+    if not credit_card_number.isdigit():
+        print(error_message + "Contains alphabets or special characters")
+        return False
+
+    credit_card_number_length = len(credit_card_number)
+    if credit_card_number_length < 13 and credit_card_number_length > 16:
+        print(error_message + "Check number length")
+        return False
+
+    if not validate_initial_digits(credit_card_number):
+        print(error_message + "Check starting number")
+        return False
+
+    if not luhn_validation(credit_card_number):
+        print(error_message + "Invalid Number")
+        return False
+
+    print(f"Given number({number}) is Valid")
+    return True
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()