must read to get the string if the length is zero we simply return an empty string otherwisewe attempt to read the specified number of bytes if we don' get any data or if the data is not the size we expected ( it is too little)we raise valueerror exception if we have the right number of bytes we create suitable format string for the struct unpack(functionand we return the string that results from unpacking the data and decoding the bytes as utf- (in theorywe could replace the last two lines with return data decode("utf ")but we prefer to go through the unpacking process since it is possible--though unlikely--that the "sformat performs some transformation on our data which must be reversed when reading back we will now look at the rest of the import_binary(methodbreaking it into two parts for ease of explanation fh none tryfh open(filename"rb"magic fh read(len(gzip_magic)if magic =gzip_magicfh close(fh gzip open(filename"rb"elsefh seek( magic fh read(len(magic)if magic !magicraise valueerror("invalid aib file format"version fh read(len(format_version)if version format_versionraise valueerror("unrecognized aib file version"self clear(the file may or may not be compressedso we use the same technique that we used for reading pickles to open the file using gzip open(or the built-in open(function once the file is open and we are at the beginningwe read the first four bytes (len(magic)if these don' match our magic number we know that it isn' binary aircraft incident data file and so we raise valueerror exception next we read in the -byte version number it is at this point that we would use different reading code depending on the version here we just check that the version isn' later one than this program is able to read if the magic number is correct and the version is one we can handlewe are ready to read in the dataso we begin by clearing out all the existing incidents so that the dictionary is empty