Various functions for use with barcodes.
Calculates the check digit for a UPC-style barcode, and returns it.
Expands upce (which is assumed to be a valid UPC-E barcode) into its full UPC-A equivalent. The return value will have either 11 or 12 digits, depending on include_check_digit.
Returns a dictionary whose keys are the barcodes held in CAM32, and whose values are lists of item numbers associated with each barcode.