:mod:`collections` -- collection and container types
====================================================

**Limitations:** Not implemented on the smallest CircuitPython boards for space reasons.

.. module:: collections
   :synopsis: collection and container types

|see_cpython_module| :mod:`python:collections`.

This module implements advanced collection and container types to
hold/accumulate various objects.

Classes
-------

.. class:: deque(iterable, maxlen[, flag])

    Deques (pronounced "deck" and short for "double-ended queue") are fixed length
    list-like containers that support O(1) appends and pops from either side of the
    deque.  New deques are created using the following arguments:

        - *iterable* must be specified as an empty or non-empty iterable.
          If the iterable is empty, the new deque is created empty.  If the
          iterable is not empty, the new deque is created with the items
          from the iterable.

        - *maxlen* must be specified and the deque will be bounded to this
          maximum length.  Once the deque is full, any new items added will
          discard items from the opposite end.

        - *flag* is optional and can be set to 1 to check for overflow when
          adding items.  If the deque is full and overflow checking is enabled,
          an ``IndexError`` will be raised when adding items.

    Deque objects have the following methods:

    .. method:: deque.append(x)

        Add *x* to the right side of the deque.
        Raises ``IndexError`` if overflow checking is enabled and there is
        no more room in the queue.

    .. method:: deque.appendleft(x)

        Add *x* to the left side of the deque.
        Raises ``IndexError`` if overflow checking is enabled and there is
        no more room in the queue.

    .. method:: deque.pop()

        Remove and return an item from the right side of the deque.
        Raises ``IndexError`` if no items are present.

    .. method:: deque.popleft()

        Remove and return an item from the left side of the deque.
        Raises ``IndexError`` if no items are present.

    .. method:: deque.extend(iterable)

        Extend the right side of the deque by appending items from the ``iterable`` argument.
        Raises IndexError if overflow checking is enabled and there is no more room left
        for all of the items in ``iterable``.

    In addition to the above, deques support iteration, ``bool``, ``len(d)``, ``reversed(d)``,
    membership testing with the ``in`` operator, and subscript references like ``d[0]``.
    Note: Indexed access is O(1) at both ends but slows to O(n) in the middle of the deque,
    so for fast random access use a ``list`` instead.

.. function:: namedtuple(name, fields)

    This is factory function to create a new namedtuple type with a specific
    name and set of fields. A namedtuple is a subclass of tuple which allows
    to access its fields not just by numeric index, but also with an attribute
    access syntax using symbolic field names. Fields is a sequence of strings
    specifying field names. For compatibility with CPython it can also be a
    a string with space-separated field named (but this is less efficient).
    Example of use::

        from collections import namedtuple

        MyTuple = namedtuple("MyTuple", ("id", "name"))
        t1 = MyTuple(1, "foo")
        t2 = MyTuple(2, "bar")
        print(t1.name)
        assert t2.name == t2[1]

.. class:: OrderedDict(...)

    ``dict`` type subclass which remembers and preserves the order of keys
    added. When ordered dict is iterated over, keys/items are returned in
    the order they were added::

        from collections import OrderedDict

        # To make benefit of ordered keys, OrderedDict should be initialized
        # from sequence of (key, value) pairs.
        d = OrderedDict([("z", 1), ("a", 2)])
        # More items can be added as usual
        d["w"] = 5
        d["b"] = 3
        for k, v in d.items():
            print(k, v)

    Output::

        z 1
        a 2
        w 5
        b 3