"""See this module if you like to store object s that have an ``id`` attribute.
"""
from collections import OrderedDict
[docs]class IdCollection(object):
"""This is a collections of object that have an ``id`` attribute."""
[docs] def __init__(self):
"""Create a new :class:`IdCollection` with no arguments.
You can add objects later using the method :meth:`append`.
"""
self._items = OrderedDict()
[docs] def append(self, item):
"""Add an object to the end of the :class:`IdCollection`.
:param item: an object that has an id
"""
self._items[item.id] = item
[docs] def at(self, index):
"""Get the object at an :paramref:`index`.
:param int index: the index of the object
:return: the object at :paramref:`index`
"""
keys = list(self._items.keys())
key = keys[index]
return self[key]
[docs] def __getitem__(self, id_):
"""Get the object with the :paramref:`id`
.. code:: python
ic = IdCollection()
ic.append(object_1)
ic.append(object_2)
assert ic[object_1.id] == object_1
assert ic[object_2.id] == object_1
:param id_: the id of an object
:return: the object with the :paramref:`id`
:raises KeyError: if no object with :paramref:`id` was found
"""
return self._items[id_]
[docs] def __bool__(self):
""":return: whether there is anything in the collection.
:rtype: bool
"""
return bool(self._items)
[docs] def __iter__(self):
"""allows you to iterate and use for-loops
The objects in the iterator have the order in which they were appended.
"""
for id_ in self._items:
yield self[id_]
[docs] def __len__(self):
""":return: the number of objects in this collection"""
return len(self._items)
@property
def first(self):
"""The first element in this collection.
:return: the first element in this collection
:raises IndexError: if this collection is empty
"""
return self.at(0)