lists.txt

.. _RefListClasses:

Lists
============================================================================

This section describes the following classes:

 * :class:`dragonfly.grammar.list.ListBase` -- the base list class
 * :class:`dragonfly.grammar.list.List` -- sub-class of Python's built-in
   ``list`` type. It can be updated and modified without reloading a
   grammar.
 * :class:`dragonfly.grammar.list.DictList` -- sub-class of Python's
   built-in ``dict`` type. It can be updated and modified without reloading
   a grammar.

The :ref:`RefListUpdates` section discusses possible performance issues with
modifying Dragonfly lists and ways to avoid these issues altogether.


List classes
----------------------------------------------------------------------------

.. automodule:: dragonfly.grammar.list
   :members:
   :member-order: bysource
   :inherited-members:


.. _RefListUpdates:

List Updates
----------------------------------------------------------------------------

Lists are updated after each modifying operation, e.g. ``list.append()``,
``list.remove()``, ``dict[key] = value``, ``dict.pop()``, etc. This is fine
for a few list modifications here and there, but is inefficient for adding /
removing many items at once.

The simplest solution is to use the :class:`ListBase` context manager::

  # Do list modification inside a 'with' block to only do one list update
  # at the end.
  my_list = List("my_list")
  with my_list:
      for x in range(50):
          my_list.append(str(x))


Some methods like ``list.extend()`` or ``dict.update()`` will also only
update the list once afterwards::

  # Add multiple list items using extend().
  my_list = List("my_list")
  my_list.extend([str(x) for x in range(50)])

  # Add multiple dictionary keys using update().
  dictionary = DictList("dictionary")
  dictionary.update({str(x):x for x in range(50)})