In [186]:

    

def credit():
    print "Please enter Visa or Amex credit card: "
    card=raw_input()
    card_rev=card[::-1]
    total = 0
    
    for i in card_rev[1::2]:
        #print "Printing i %s"  %i
        x= int(i)*2
        if len(str(x)) == 2:
            for a in str(x):
                #print "Printing a %s" %a
                total += int(a)
                #print "Printing subtotal %s" %total
        else:
            total +=int(x)
            #print "Printing total %s" %total
    #print total
    
    for i in card_rev[::2]:
        total += int(i)
        #print total
    
    
    #print total
    
    if ((len(card) == 16 or len(card) == 13 ) and int(card[0]) == 4 and (total  % 10 == 0 )) or \
            (len(card) == 15 and (int(card[:2]) == 34 or int(card[:2]) == 37) and (total % 10 == 0 )):
            
        print "This is a valid Credit Card"
        
    else:
        print "Invalid credit card"


    

In [187]:

    

credit()


    

    




Please enter Visa or Amex credit card: 
4111111111111111
This is a valid Credit Card

In [126]:

    

test='4111111111111111'


    

In [139]:

    

test[::-1][1::2]


    

    
Out[139]:





'0241687'

In [183]:

    

test_2='371449635398431'


    

In [162]:

    

test_2[::-1][::2]


    

    
Out[162]:





'40555093'

In [167]:

    

test_2[::-1][1::2]


    

    
Out[167]:





'0241687'

In [ ]: