Credit Card Validator done

Author: Karan Goel

Numbers/credit_card_validator.py

@@ -0,0 +1,41 @@
+"""
+Credit Card Validator - Takes in a credit card number from a
+common credit card vendor (Visa, MasterCard, American Express,
+Discoverer) and validates it to make sure that it is a valid
+number (look into how credit cards use a checksum).
+
+This program works with *most* credit card numbers.
+
+Uses Luhn Algorithm (http://en.wikipedia.org/wiki/Luhn_algorithm).
+
+1. From the rightmost digit, which is the check digit, moving
+left, double the value of every second digit; if product of this
+doubling operation is greater than 9 (e.g., 7 * 2 = 14), then
+sum the digits of the products (e.g., 10: 1 + 0 = 1, 14: 1 + 4 = 5).
+
+2. Add together doubled digits with the undoubled digits from the
+original number.
+
+3. If the total modulo 10 is equal to 0 (if the total ends in zero)
+then the number is valid according to the Luhn formula; else it is
+not valid.
+"""
+
+if __name__ == '__main__':
+    number = raw_input('Enter the credit card number of check: ').replace(' ', '')
+    #if not number.isdigit():
+    #    raise Exception('Invalid credit card number. Make sure it\'s all digits (with optional spaces in between).'
+
+    digits = [int(char) for char in number]
+
+    # double alternate digits (step 1)
+    doubled = [(digit * 2) if (i % 2 == 0) else digit \
+           for (i, digit) in enumerate(digits)] # i <3 python
+    # sum digits of number > 10 (step 2)
+    summed = [num if num < 10 else sum([int(dig) for dig in str(num)]) \
+              for num in doubled] # i <3 python ** 2
+    # step 3
+    if sum(summed) % 10 == 0:
+        print 'The number is valid'
+    else:
+        print 'The number is invalid'