odict

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odict

Dictionary in which the insertion order of items is preserved (using an internal double linked list). In this implementation replacing an existing item keeps it at its original position.

Internal representation: values of the dict.

.. code-block:: python

[pred_key, val, succ_key]

The sequence of elements uses as a double linked list. The links are dict keys. self.lh and self.lt are the keys of first and last element inserted in the odict.

Motivation

When this package was created, collections.OrderedDict not existed yet.

Another problem is that dict cannot always be inherited from in conjunction with other base classes. This may result in instance layout conflicts or other errors. So odict is written in a way that let you alter the dictionary base implementation.

Usage

Import and create ordered dictionary.

.. code-block:: python

from odict import odict
od = odict()

Custom odict

It is possible to use _odict base class to implement an ordered dict not inheriting from dict type. This is useful i.e. when persisting to ZODB.

Inheriting from dict and Persistent at the same time fails. Also, using a regular list for the internal double linked list representation causes problems, so we define a custom class for it as well.

.. code-block:: python

from persistent.dict import PersistentDict
from persistent.list import PersistentList

class podict(_odict, PersistentDict):

    def _dict_impl(self):
        return PersistentDict

    def _list_factory(self):
        return PersistentList

Python < 3.7

In Python < 3.7 casting to dict will fail. The reason for this can be found here <http://bugs.python.org/issue1615701>_. The __init__ function of dict checks whether arg is subclass of dict, and ignores overwritten __getitem__ & co if so. This was fixed and later reverted due to behavioural problems with pickle:

.. code-block:: pycon

>>> dict(odict([(1, 1)]))
{1: [nil, 1, nil]}

Use one of the following ways for type conversion.

.. code-block:: pycon

>>> dict(odict([(1, 1)]).items())
{1: 1}

>>> odict([(1, 1)]).as_dict()
{1: 1}

Misc

In a C reimplementation of this data structure, things could be simplified (and speed up) a lot if given a value you can at the same time find its key. With that, you can use normal C pointers.

Python Versions

• Python 2.7, 3.7+

• Probably works with other/older versions

Contributors

• bearophile (Original Author)

• Robert Niederreiter (Author)

• Georg Bernhard

• Florian Friesdorf

• Jens Klein

under the Python Software Foundation License <http://www.opensource.org/licenses/PythonSoftFoundation.php>_.

Changes

1.9.0 (2022-05-15)

• Add movebefore, moveafter, movefirst and movelast functions to odict. [rnix]

• Use first_key and last_key in insertfirst and insertlast instead of reading all keys. [rnix]

1.8.1 (2022-03-17)

• Do not run test suites for Python 2.6 and Python < 3.7 any more. No changes to the implementation have been made. [rnix]

• Package housekeeping. [rnix]

1.8.0

• Add next_key and prev_key functions. [rnix]

• Add first_key and last_key properties. [rnix]

• Add _list_factory on _odict base class. Can be used to alter the list implementation used for internal value triples. [rnix]

1.7.0

• Add swap, insertbefore, insertafter, insertfirst and insertlast functions to odict. [rnix]

1.6.2

• Use class name instead of 'odict()' in __repr__. [rnix]

1.6.1

• pypi masness. [rnix]

1.6.0

• Compatible with Python 3 and pypy. [rnix]

1.5.2

• Fix permission problem in 1.5.1 release, some files were only rw by user. [jensens, 2016-11-25]

1.5.1

• Implement __copy__ and __deepcopy__ in order to work with Python 2.7. [rnix, 2012-10-15]

• Use try/except instead of in in __contains__. [rnix, 2012-10-15]

1.5.0

• Implement alter_key. [rnix, 2012-05-18]

1.4.4

• Remove unused error variable. [rnix, 2011-11-28]

• Add note on why to check with == and != against _nil. [rnix, 2011-11-28]

1.4.3

• Get rid of annoying warning about "global" usage in bench.py. [jensens, 2011-09-20]

1.4.2

• More copy testing. [rnix, 2010-12-18]

• Add has_key to odict. [rnix, 2010-12-18]

1.4.1

• Fix release, README.rst was missing, added MANIFEST.in file to include it. [jensens, 2010-11-29]

1.4.0

• Full test coverage. [chaoflow, rnix, 2010-08-17]

• Code cleanup and optimizing. [chaoflow, rnix, 2010-08-17]

1.3.2

• Access dict API providing class via function _dict_impl() and provide odict logic as abstract base class _odict. [rnix, 2010-07-08]

1.3.1

• Add test for bool evaluation. [rnix, 2010-04-21]

1.3.0

• Fix access to odict.lt and odict.lh properties. Now it's possible to overwrite __setattr__ and __getattr__ on odict subclass without hassle. [rnix, 2010-04-06]

• Add sort function to odict. [rnix, 2010-03-03]

1.2.6

• Make odict serialize and deserialize properly. [gogo, 2010-01-12]

1.2.5

• Add as_dict function. Supports type conto ordinary dict. [rnix, 2009-12-19]

• Add benchmark script. [rnix, 2009-12-19]

1.2.4

• Do not check for key in self on __delitem__, KeyError is raised properly anyway. Huge Speedup! [rnix, jensens, 2009-12-18]

1.2.3

• Move tests to seperate file and make egg testable with python setup.py test. [rnix, 2009-12-07]

• improve lt and lh properties to make odict work with copy.deepcopy. [rnix, 2009-12-07]

1.2.2

• Use try/except instead of __iter__ in __setitem__ to determine if value was already set. [rnix, 2009-07-17]

1.2.1

• Add missing __len__ and __contains__ functions. [rnix, 2009-03-17]

1.2.0

• Eggified [rnix, 2009-03-17]

< 1.2

• http://code.activestate.com/recipes/498195/ [bearophile, 2006-10-12]

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