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Date: Wed, 22 Jul 2015 20:11:47 -0600
From: Michael Torrie <torriem@gmail.com>
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Subject: Re: Integers with leading zeroes
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On 07/22/2015 07:51 AM, Grant Edwards wrote:
> On 2015-07-22, Ben Finney <ben+python@benfinney.id.au> wrote:
>> Laura Creighton <lac@openend.se> writes:
>>
>>> The biggest use I have for decimal numbers that begin with 0 is in
>>> credit card numbers, account numbers and the like where the first
>>> check you do is 'does this thing have the correct number of digits'.
>>
>> The following are examples of types from the real world that people
>> think of, and casually discuss, as “numbers”.
>>
>> * Postal code
>> * Credit card number
>> * Telephone number
>> * Car registration plate number
>> * Personal Identification Number (PIN)
> 
> Those are all strings.  Not numbers.

That depends.  A credit card number is indeed a number, and there are
mathematical formulas for determining if a particular number is a valid
(as in well-formed) credit card number, and possibly to identify what
kind of card it is.