How do you check in python whether a string contains only numbers?

How do you check whether a string contains only numbers?

I've given it a go here. I'd like to see the simplest way to accomplish this.

    import string

    def main():
        isbn = input("Enter your 10 digit ISBN number: ")
        if len(isbn) == 10 and string.digits == True:
            print ("Works")
            print("Error, 10 digit number was not inputted and/or letters were inputted.")

    if __name__ == "__main__":
        input("Press enter to exit: ")

You'll want to use the isdigit method on your str object:

    if len(isbn) == 10 and isbn.isdigit():

From the isdigit documentation:

>     str.isdigit()

Return true if all characters in the string are digits and there is at least one character, false otherwise.

For 8-bit strings, this method is locale-dependent.