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.. _dec private modes:
DEC Private Modes
=================
DEC Private Modes are terminal control sequences that enable or disable specific
terminal behaviors like cursor visibility, mouse tracking, alternate screen
buffers, and modern features like synchronized output.
The blessed library provides a clean API for working with these modes:
* Query mode support with :meth:`~blessed.Terminal.get_dec_mode`
* Enable modes with :meth:`~blessed.Terminal.dec_modes_enabled` context manager
* Disable modes with :meth:`~blessed.Terminal.dec_modes_disabled` context manager
Each mode is identified by a constant from
:attr:`Terminal.DecPrivateMode <blessed.Terminal.DecPrivateMode>`.
Our mode catalog is derived from https://wiki.tau.garden/dec-modes/
Overview
--------
DEC Private Modes control a wide variety of terminal features. Some common
examples include:
* **DECTCEM** (25) - Cursor visibility
* **MOUSE_REPORT_CLICK** (1000) - Basic mouse click reporting
* **MOUSE_EXTENDED_SGR** (1006) - Extended mouse reporting with pixel coordinates
* **BRACKETED_PASTE** (2004) - Receive clipboard paste as a single event
* **FOCUS_IN_OUT_EVENTS** (1004) - Detect when terminal window gains/loses focus
* **SYNCHRONIZED_OUTPUT** (2026) - Eliminate screen flicker during redraws
The context managers gracefully handle unsupported modes - your code works
normally even on terminals that don't support specific features.
Timeout Behavior
----------------
All DEC mode context managers use a default ``timeout`` of 1 second when querying
mode support. This timeout is designed to handle "dumb" terminals that don't
support DEC mode queries and won't respond.
The timeout delay only occurs on the **first** call to any mode query method,
as subsequent calls use cached results. Unsupported modes are gracefully
ignored - your code continues to work even when a terminal doesn't support
a specific feature.
You can verify mode support quickly using :meth:`~blessed.Terminal.get_dec_mode`
(see :ref:`querying mode support` below), which also benefits from caching after
the first query.
Getting Started
---------------
Here's a simple example that temporarily hides the cursor:
.. literalinclude:: ../bin/dec_modes_simple.py
:language: python
:linenos:
The cursor automatically reappears when the context exits, even if an exception
occurs.
This usually emits the same sequences recorded in the terminfo database of
modern terminals for the ``term.hide_cursor`` and ``term.normal_cursor``
attributes and offered by our context manager method,
:meth:`~Terminal.hidden_cursor`.
The difference is that we can also make inquiries into the whether the mode is
supported at all.
.. _querying mode support:
Querying Mode Support
----------------------
You can check if a terminal supports a specific mode using
:meth:`~blessed.Terminal.get_dec_mode`. This is useful for adapting your
application to different terminal capabilities:
.. literalinclude:: ../bin/dec_modes_query.py
:language: python
:linenos:
The ``timeout`` value is unspecified and defaults to 1 second. If a Terminal
fails to respond in this amount of time, the special property ``failed`` becomes
``True``.
The :class:`~blessed.dec_modes.DecModeResponse` object provides helper properties:
* :attr:`~blessed.dec_modes.DecModeResponse.supported` - Mode is recognized
* :attr:`~blessed.dec_modes.DecModeResponse.enabled` - Mode is currently active
* :attr:`~blessed.dec_modes.DecModeResponse.disabled` - Mode is currently inactive
* :attr:`~blessed.dec_modes.DecModeResponse.permanent` - Mode setting cannot be changed
* :attr:`~blessed.dec_modes.DecModeResponse.failed` - Query failed or timed out
Query results are automatically cached. Use ``force=True`` to bypass the cache:
Try the :ref:`display_modes.py` example program to detect and report all supported
sequences for a given terminal.
Context Managers
----------------
The recommended way to work with modes is through context managers:
* :meth:`~blessed.Terminal.dec_modes_enabled` - Temporarily enable one or more modes
* :meth:`~blessed.Terminal.dec_modes_disabled` - Temporarily disable one or more modes
These context managers:
1. Query the Terminal's support for a mode within given timeout
2. Change the mode if allowed by negotiation
3. Restore the original state on exit if changed
4. Handle unsupported modes gracefully
You can pass multiple modes to enable them simultaneously:
.. code-block:: python
with term.dec_modes_enabled(
term.DecPrivateMode.DECTCEM,
term.DecPrivateMode.MOUSE_REPORT_CLICK,
):
# Both modes enabled here
pass
For commonly-used DEC modes, blessed provides convenient context managers on the
:class:`~.Terminal` object that make accessing them easier.
These convenience wrappers all contain a default ``timeout`` argument of 1.
Given this, for terminals that do not support DEC Mode negotiation, the first
call will cause up to a 1 second delay while awaiting a possible terminal
response to confirm support.
All subsequent calls use a cache of the failed query result and incur no further
delays.
.. _Synchronized Output:
Synchronized Output
-------------------
Synchronized Output (mode 2026) eliminates screen flicker by buffering all
output until the mode is exited. This is perfect for animations and full-screen
redraws.
Without synchronized output, rapidly clearing and redrawing the screen creates
a visible blink effect. With it, updates appear instantly:
.. literalinclude:: ../bin/dec_modes_synchronized.py
:language: python
:linenos:
On terminals that support this mode, you'll just see screen of ``fill`` characters
with a counter in the top-left corner. On terminals that do not support it,
partial draws of ``empty`` spaces will cause the screen to occasionally blink or
flash.
Bracketed Paste
---------------
Bracketed Paste (mode 2004) allows your application to receive clipboard paste
operations as a single event rather than a stream of individual characters.
This makes it easy to distinguish between typed and pasted text:
.. literalinclude:: ../bin/dec_modes_bracketed_paste.py
:language: python
:linenos:
When :attr:`Keystroke.mode` equals
:attr:`~blessed.dec_mode.DecPrivateMode.BRACKETED_PASTE`, the
:meth:`~.Keystroke.mode_values` method returns a
:class:`~blessed.keyboard.BracketedPasteEvent` with a ``text`` attribute
containing the pasted content.
Focus Events
------------
Focus tracking (mode 1004) reports when the terminal window gains or loses
focus. This is useful for pausing animations or updating status indicators:
.. literalinclude:: ../bin/dec_modes_focus.py
:language: python
:linenos:
When :attr:`Keystroke.mode` equals
:attr:`~blessed.dec_mode.DecPrivateMode.FOCUS_IN_OUT_EVENTS`, the
:meth:`~.Keystroke.mode_values` method returns a
:class:`~blessed.keyboard.FocusEvent` with a ``gained`` attribute indicating
whether focus was gained (``True``) or lost (``False``).
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