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.. _advanced-containers:
Atom's containers
=================
.. include:: ../substitutions.sub
Atom uses custom containers to implement type validation and notifications. It
implements two list subclasses and one dictionary subclass to this effect.
.. note::
Currently the typed validated dictionary is not a subclass of the Python
builtin dictionary type. This can cause some unexpected issues in
particular when assigning the value stored in a |Dict| member to another
|Dict| which will fail. To circumvent this issue one should call ``dict``
on the content of the first member.
This is a known problem and will be fixed in a future version of atom.
Usually, users should not instantiate those containers manually, in particular
because they need a reference to both the member and the instance to which
they are tied.
Atom provides however an alternative mapping type which uses less memory than
a regular dictionary in particular when the mapping contain only few objects:
|sortedmap|.
|sortedmap|
-----------
|sortedmap| can be imported from ``atom.datastructures.api``. Contrary to a
regular Python dictionary, |sortedmap| does not requires the keys to be
hashable, however they should be sortable. |sortedmap| will fall back on the
Python 2 behavior to order any Python object based on the class name and the
object id if two objects cannot be compared otherwise.
In terms of memory efficiency, here is a quick comparison:
+-------------+-------------+---------------+
| | dict | sortedmap |
+=============+=============+===============+
| empty | 240 | 72 |
+-------------+-------------+---------------+
| 1 key | 240 | 88 |
+-------------+-------------+---------------+
| 2 key | 240 | 104 |
+-------------+-------------+---------------+
| 100 key | 4704 | 2120 |
+-------------+-------------+---------------+
|sortedmap| is not meant to replace dictionaries but can be valuable
when a large number of small containers is necessary.
|
