Python: splitting an integer into digits

Question

I'm writing a program which calculates the check digit of an ISBN number. I have to read the user's input (nine digits of an ISBN) into an integer variable, and then multiply the last digit by 2, the second last digit by 3 and so on. How can I "split" the integer into its constituent digits to do this? As this is a basic exercise I am not supposed to use a list.

Answer 1

Just create a string out of it.

myinteger = 212345
number_string = str(myinteger)

That's enough. Now you can iterate over it:

for ch in number_string:
    print ch # will print each digit in order

Or you can slice it:

print number_string[:2] # first two digits
print number_string[-3:] # last three digits
print number_string[3] # forth digit

---

Or better, don't convert the user's input to an integer (the user types a string)

isbn = raw_input()
for pos, ch in enumerate(reversed(isbn)):
    print "%d * %d is %d" % pos + 2, int(ch), int(ch) * (pos + 2)

For more information read a tutorial.

Answer 2

list_of_ints = [int(i) for i in str(ISBN)]

Will give you a sorted list of ints. Of course, given duck typing, you might as well work with str(ISBN).

Edit: As mentioned in the comments, this list isn't sorted in the sense of being ascending or descending, but it does have a defined order (sets, dictionaries, etc in python in theory don't, although in practice the order tends to be fairly reliable). If you want to sort it:

list_of_ints.sort()

is your friend. Note that sort() sorts in place (as in, actually changes the order of the existing list) and doesn't return a new list.

Answer 3

while number:
    digit = number % 10
    # do whatever with digit
    number /= 10

On each iteration of the loop, it removes the last digit from number, assigning it to $digit. It's in reverse, starts from the last digit, finishes with the first

Answer 4

How about a one-liner list of digits...

ldigits = lambda n, l=[]: not n and l or l.insert(0,n%10) or ldigits(n/10,l)

Answer 5

On Older versions of Python...

map(int,str(123))

On New Version 3k

list(map(int,str(123)))