Python in a Nutshell, 2nd Edition

Interactive Command Sessions

The cmd module offers a simple way to handle interactive sessions of commands. Each command is a line of text. The first word of each command is a verb defining the requested action. The rest of the line is passed as an argument to the method that implements the verb’s action.

Module cmd supplies class Cmd to use as a base class, and you define your own subclass of cmd.Cmd. Your subclass supplies methods with names starting with do_ and help_, and may optionally override some of Cmd’s methods. When the user enters a command line such as verb and the rest, as long as your subclass defines a method named do_verb, Cmd.onecmd calls:

self.do_verb('and the rest')

Similarly, as long as your subclass defines a method named help_verb, Cmd.do_help calls the method when the command line starts with 'help verb' or '?verb'. Cmd, by default, shows suitable error messages if the user tries to use, or asks for help about, a verb for which the subclass does not define the needed method.

Initializing a Cmd Instance

Your subclass of cmd.Cmd, if it defines its own _ _init_ _ special method, must call the base class’s _ _init_ _, whose signature is as follows.

_ _init_ _

Cmd._ _init_ _(self, completekey='Tab', stdin=sys.stdin, stdout=sys.stdout) Initializes instance self with specified or default values for completekey (name of the key to use for command completion with the readline module; pass None to disable command completion), stdin (file object to get input from), and stdout ...