Settings
========

Settings provide a mechanism for a user to control the behavior of a ``cmd2``
based application. A setting is stored in an instance attribute on your
subclass of :class:`cmd2.Cmd` and must also appear in the
:attr:`cmd2.Cmd.settable` dictionary. Developers may set default values
for these settings and users can modify them at runtime using the
:ref:`features/builtin_commands:set` command. Developers can
:ref:`features/settings:Create New Settings` and can also
:ref:`features/settings:Hide Builtin Settings` from the user.


Builtin Settings
-----------------

``cmd2`` has a number of builtin settings. These settings control the behavior
of certain application features and :ref:`features/builtin_commands:Builtin
Commands`. Users can use the :ref:`features/builtin_commands:set` command to
show all settings and to modify the value of any setting.


allow_style
~~~~~~~~~~~

Output generated by ``cmd2`` programs may contain ANSI escape seqences which
instruct the terminal to apply colors or text styling (i.e. bold) to the
output. The ``allow_style`` setting controls the behavior of these escape
sequences in output generated with any of the following methods:

- :meth:`cmd2.Cmd.poutput`
- :meth:`cmd2.Cmd.perror`
- :meth:`cmd2.Cmd.pwarning`
- :meth:`cmd2.Cmd.pexcept`
- :meth:`cmd2.Cmd.pfeedback`
- :meth:`cmd2.Cmd.ppaged`

This setting can be one of three values:

- ``Never`` - all ANSI escape sequences which instruct the terminal to style
  output are stripped from the output.

- ``Terminal`` - (the default value) pass through ANSI escape sequences when
  the output is being sent to the terminal, but if the output is redirected to
  a pipe or a file the escape sequences are stripped.

- ``Always`` - ANSI escape sequences are always passed through to the output


debug
~~~~~

The default value of this setting is ``False``, which causes the
:meth:`~cmd2.Cmd.pexcept` method to only display the message from an
exception. However, if the debug setting is ``True``, then the entire stack
trace will be printed.


echo
~~~~

If ``True``, each command the user issues will be repeated to the screen
before it is executed. This is particularly useful when running scripts.
This behavior does not occur when running a command at the prompt.


editor
~~~~~~

Similar to the ``EDITOR`` shell variable, this setting contains the name of the
program which should be run by the :ref:`features/builtin_commands:edit`
command.


feedback_to_output
~~~~~~~~~~~~~~~~~~

Controls whether feedback generated with the :meth:`~cmd2.Cmd.pfeedback`
method is sent to ``sys.stdout`` or ``sys.stderr``. If ``False`` the output
will be sent to ``sys.stderr``

If ``True`` the output is sent to ``stdout`` (which is often the screen but may
be :ref:`redirected <features/redirection:Output Redirection and Pipes>`). The
feedback output will be mixed in with and indistinguishable from output
generated with :meth:`~cmd2.Cmd.poutput`.


max_completion_items
~~~~~~~~~~~~~~~~~~~~

Maximum number of CompletionItems to display during tab completion. A
CompletionItem is a special kind of tab completion hint which displays both a
value and description and uses one line for each hint. Tab complete the ``set``
command for an example.

If the number of tab completion hints exceeds ``max_completion_items``, then
they will be displayed in the typical columnized format and will not include
the description text of the CompletionItem.


quiet
~~~~~

If ``True``, output generated by calling :meth:`~cmd2.Cmd.pfeedback` is
suppressed. If ``False``, the :ref:`features/settings:feedback_to_output`
setting controls where the output is sent.


timing
~~~~~~

If ``True``, the elapsed time is reported for each command executed.


Create New Settings
-------------------

Your application can define user-settable parameters which your code can
reference. In your initialization code:

1. Create an instance attribute with a default value.
2. Create a :class:`.Settable` object which describes your setting.
3. Pass the :class:`.Settable` object to :meth:`cmd2.Cmd.add_settable`.

Here's an example, from
``examples/environment.py``:

.. literalinclude:: ../../examples/environment.py

If you want to be notified when a setting changes (as we do above), then be
sure to supply a method to the ``onchange_cb`` parameter of the
`.cmd2.utils.Settable`. This method will be called after the user
changes a setting, and will receive both the old value and the new value.

.. code-block:: text

   (Cmd) set --long | grep sunny
   sunny: False                # Is it sunny outside?
   (Cmd) set --long | grep degrees
   degrees_c: 22               # Temperature in Celsius
   (Cmd) sunbathe
   Too dim.
   (Cmd) set degrees_c 41
   degrees_c - was: 22
   now: 41
   (Cmd) set sunny
   sunny: True
   (Cmd) sunbathe
   UV is bad for your skin.
   (Cmd) set degrees_c 13
   degrees_c - was: 41
   now: 13
   (Cmd) sunbathe
   It's 13 C - are you a penguin?


Hide Builtin Settings
---------------------

You may want to prevent a user from modifying a builtin setting. A setting
must appear in the :attr:`cmd2.Cmd.settable` dictionary in order for it
to be available to the :ref:`features/builtin_commands:set` command.

Let's say that you never want end users of your program to be able to enable
full debug tracebacks to print out if an error occurs. You might want to hide
the :ref:`features/settings:debug` setting. To do so, remove it from the
:attr:`cmd2.Cmd.settable` dictionary after you initialize your object.
The :meth:`cmd2.Cmd.remove_settable` convenience method makes this easy::

  class MyApp(cmd2.Cmd):

    def __init__(self):
        super().__init__()
        self.remove_settable('debug')
