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.. cmd2 documentation for application and command lifecycle and the hooks which are available
cmd2 Application Lifecyle 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.Cmd.preloop
.. automethod:: cmd2.Cmd.postloop
Application Lifecycle Attributes
--------------------------------
There are numerous attributes (member variables of the ``cmd2.Cmd``) which have a signficiant effect on the applicaiton
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 applicatoin 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.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
applicaiton-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.Cmd.preparse
.. automethod:: cmd2.Cmd.postparse
.. automethod:: cmd2.Cmd.postparsing_precmd
.. automethod:: cmd2.Cmd.precmd
.. automethod:: cmd2.Cmd.postcmd
.. automethod:: cmd2.Cmd.postparsing_postcmd
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