S10 (UPU standard)

The UPU S10 standard defines a system for assigning 13-character identifiers to international postal items for the purpose of tracking and tracing them during shipping.

With increased liberalization and the possibility of multiple postal services operating in the same country, the use of country codes to designate the postal service is a problem. To solve this, each country has a designated postal service that controls all S10 identifiers from that country; any competing postal services will have to cooperate with the designated owner. The organization assigned by the UPU member country shall manage the issue and use of S10 identifiers, among all the operators under the authority of that UPU member country, in such a way as to ensure that no S10 identifier is reused within a period of 12 calendar months. A period of 24 calendar months, or longer, is recommended.

Format
The identifiers consist of a two-letter service indicator code, an eight-digit serial number (in the range 00000000 to 99999999), a single check-digit, and a two-letter ISO country code identifying the issuing postal administration's country.

Service indicator codes
Service codes are generally assigned and administered within each issuing country, but certain types of service and code ranges are used for all countries as listed here.

Check-digit calculation

 * 1) Ignore the service indicator code and country code.
 * 2) Assign the weights 8, 6, 4, 2, 3, 5, 9, 7 to the 8 digits, from left to right.
 * 3) Calculate S, the sum of each digit multiplied by its weight.
 * 4) * For example, for the number 47312482: S = 4×8 + 7×6 + 3×4 + 1×2 + 2×3 + 4×5 + 8×9 + 2×7 = 200.
 * 5) Calculate the check digit C = 11 − (S mod 11).
 * 6) * If C = 10, change to C = 0.
 * 7) * If C = 11, change to C = 5.
 * 8) * For the example 47312482, C = 11 − (200 mod 11) = 11 − 2 = 9.

Python code for check-digit calculation
For Python 3.6 or later: