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.. cmd2 documentation for application and command lifecycle and the hooks which are available
cmd2 Application Lifecycle and Hooks
====================================
The typical way of starting a cmd2 application is as follows::
from cmd2 import Cmd
class App(Cmd):
# customized attributes and methods here
app = App()
app.cmdloop()
There are several pre-existing methods and attributes which you can tweak to control the overall behavior of your
application before, during, and after the main loop.
Application Lifecycle Hook Methods
----------------------------------
The ``preloop`` and ``postloop`` methods run before and after the main loop, respectively.
.. automethod:: cmd2.cmd2.Cmd.preloop
.. automethod:: cmd2.cmd2.Cmd.postloop
Application Lifecycle Attributes
--------------------------------
There are numerous attributes (member variables of the ``cmd2.Cmd``) which have a significant effect on the application
behavior upon entering or during the main loop. A partial list of some of the more important ones is presented here:
- **intro**: *str* - if provided this serves as the intro banner printed once at start of application, after ``preloop`` runs
- **allow_cli_args**: *bool* - if True (default), then searches for -t or --test at command line to invoke transcript testing mode instead of a normal main loop
and also processes any commands provided as arguments on the command line just prior to entering the main loop
- **echo**: *bool* - if True, then the command line entered is echoed to the screen (most useful when running scripts)
- **prompt**: *str* - sets the prompt which is displayed, can be dynamically changed based on application state and/or
command results
Command Processing Hooks
------------------------
Inside the main loop, every time the user hits <Enter> the line is processed by the ``onecmd_plus_hooks`` method.
.. automethod:: cmd2.cmd2.Cmd.onecmd_plus_hooks
As the ``onecmd_plus_hooks`` name implies, there are a number of *hook* methods that can be defined in order to inject
application-specific behavior at various points during the processing of a line of text entered by the user. ``cmd2``
increases the 2 hooks provided by ``cmd`` (**precmd** and **postcmd**) to 6 for greater flexibility. Here are
the various hook methods, presented in chronological order starting with the ones called earliest in the process.
.. automethod:: cmd2.cmd2.Cmd.preparse
.. automethod:: cmd2.cmd2.Cmd.postparse
.. automethod:: cmd2.cmd2.Cmd.postparsing_precmd
.. automethod:: cmd2.cmd2.Cmd.precmd
.. automethod:: cmd2.cmd2.Cmd.postcmd
.. automethod:: cmd2.cmd2.Cmd.postparsing_postcmd
Registering hooks
-----------------
As an alternative to overriding one of the hook methods, you can register any number of functions
to be called when the hook is processed. These registered functions are called before any overridden
method.
This method of registering and calling multiple hooks allows plugins to tap into the hook mechanism
without interfering with each other or with your code.
register_preloop_hook
register_postloop_hook
register_preparsing_hook
register_postparsing_hook
register_precmd_hook
register_postcmd_hook
register_cmdcompleted_hook
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