This code is a software for reading data from a Symbol CS1504 barcode scanner. It uses the pyserial library to communicate with the scanner via a serial connection. The code also includes functions for formatting ISBN codes and expanding certain barcode symbols. The supported barcode symbols and their corresponding codes are specified in the symbologies dictionary. When a barcode is scanned, the code will determine the symbology based on the code returned by the scanner and, if necessary, expand the code to the full ISBN format or perform any other necessary formatting. The format_isbn function is used to calculate and add the ISBN check digit. The expand function is used to determine if the barcode should be expanded and, if necessary, perform the expansion.