tuple type which we then return to the caller (main())which inserts the user into the users dictionaryready for printing if we had not created suitable constants to hold the index positionswe would be reduced to using numeric indexesfor exampleuser user(usernamefields[ ]fields[ ]fields[ ]fields[ ]although this is certainly shorterit is poor practice first it isn' clear to future maintainers what each field isand second it is vulnerable to data file format changes--if the order or number of fields in record changesthis code will break everywhere it is used but by using named constants in the face of changes to the record struturewe would have to change only the values of the constantsand all uses of the constants would continue to work def generate_username(fieldsusernames)username ((fields[forename][ fields[middlename][: fields[surname]replace("-"""replace("'""")username original_name username[: lower(count while username in usernamesusername "{ }{ }format(original_namecountcount + usernames add(usernamereturn username we make first attempt at creating username by concatenating the first letter of the forenamethe first letter of the middle nameand the whole surnameand deleting any hyphens or single quotes from the resultant string the code for getting the first letter of the middle name is quite subtle if we had used fields[middlename][ we would get an indexerror exception for empty middle names but by using slice we get the first letter if there is oneor an empty string otherwise next we make the username lowercase and no more than eight characters long if the username is in use ( it is in the usernames set)we try the username with " tacked on at the endand if that is in use we try with " "and so on until we get one that isn' in use then we add the username to the set of usernames and return the username to the caller def print_users(users)namewidth usernamewidth print("{ :<{nw}{ :^ { :{uw}}format"name""id""username"nw=namewidthuw=usernamewidth)print("{ :-<{nw}{ :-< { :-<{uw}}format""nw=namewidthuw=usernamewidth)