# Overview

## The ordereddict module in short

This is an implementation of an ordered dictionary with Key Insertion Order (KIO: updates of values do not affect the position of the key), Key Value Insertion Order (KVIO, an existing key's position is removed and put at the back). The standard library module OrderedDict, implemented later, implements a subset of ordereddict functionality.

Sorted dictionaries are also provided. Currently only with Key Sorted Order (KSO, no sorting function can be specified, but you can specify a transform to apply on the key before comparison (e.g. string.lower)).

This package is hosted on BitBucket and installable from PyPI:

pip install ruamel.ordereddict


For Windows there are 32 and 64 bit installable wheels available.

Usage:

from ruamel.ordereddict import ordereddict
kio = ordereddict()
kvio = ordereddict(kvio=True)
# without relax unordered initalisation is not allowed
d = ordereddict({'a':1, 'b': 2}, relax=True)
sd = sorteddict({'a':1, 'b': 2}) # sorteddict is always relaxed


please note that starting with 0.4.6 you should not import _ordereddict directly

This module has been tested under:

 OS compiler Python Linux Mint 17 gcc 4.8.4 2.7.13 Windows Visual Studio 2010 2.7.13.32 Windows Visual Studio 2010 2.7.13.64

Older versions of this module has been tested under and I expect those to still work:

 OS compiler Python Windows XP-64 Visual Studio 2010 2.7.10-32 Windows XP-64 Visual Studio 2010 2.7.10-64 Windows XP-64 Visual Studio 2008 2.6.9-32 Windows XP-64 Visual Studio 2008 2.6.9-64 Linux Mint 17 gcc 4.8.2 2.6.9 Ubuntu 12.04 gcc 4.7.2 2.7.6 Ubuntu 12.04 gcc 4.7.2 2.6.8 Ubuntu 8.04 gcc 4.2.4 2.7.6 Ubuntu 8.04 gcc 4.2.4 2.5.2 Windows XP Visual C++ 2008 Express 2.7.6 Windows 7 64 Windows SDK for Win7 SP1 2.7.6 Ubuntu 12.04 gcc 4.6.3 2.7.3 Ubuntu 8.04 gcc 4.2.4 2.6.4 Ubuntu 8.04 gcc 4.2.4 2.5.2 Ubuntu 8.10 gcc 4.3.2 2.5.4 Ubuntu 8.10 gcc 4.3.2 2.4.6 Ubuntu 7.04 gcc 4.1.2 2.5.1 Ubuntu 7.04 gcc 4.1.2 2.4.4 Ubuntu 6.06 gcc 2.5.1 Windows XP Visual Studio 2003 2.5.1 Windows XP Visual C++ 2008 Express 2.6.5 Windows MingGW 4.7.0 2.7.3 Solaris 10 GCC 4.4.x 2.7.3

Version 0.4.1 was tested and found working on SuSE Linux Enterprise Server (GCC 4.1.0 and Intel C/C++ 10.1) by Stuart Stock.

MingGW and Solaris were tested and reported to work by Wladimir with version 0.4.5

## Home

https://bitbucket.org/ruamel/ordereddict is ordereddict's home on the web.

Clone the repository there if you want to work from the source.

## Installation

You can clone and checkout the sources, and then run:

python setup.py install


## Bugreporting

If you find any problems, please let me know, but also realise that I have a spamfilter that catches over 100 emails a day and yours might get in there unnoticed. So if there is no response within a few days please try again.

## Functionality

ordereddict has all of the functionality of dict() except that there is no keyword based initialisation and that you cannot pass a normal dict to the initialisation of the basic ordereddict (however see the relax-ed keyword below). sorteddict cannot be initialised from keywords either, but can be initialised from normal dict (ie. they are always relaxed).

As you probably would expect .keys(), .values(), .items(), .iterkeys(), itervalues(), iteritems() and "for i in some_ordereddict" have elements ordered based on the key insertion order (or key value insertion order if kvio is specified, or sort order for sorteddict).

ordered/sorteddicts can be pickled.

Some methods have been slightly changed:

• initialisation of ordereddict takes keywords:
• kvio: if set to True, then move an existing key on update
• relax: if set to True, the ordereddict is relaxed for its life regarding initialisation and/or update from unordered data (read a normal dict).
• initialisation of sorteddict takes keyword:
• key: specifies a function to apply on key (e.g. string.lower)
• .popitem() takes an optional argument (defaulting to -1) indicating which key/value pair to return (by default the last one available)
• .dict()/.values()/.items()/.iterdict()/.itervalues()/.iteritems() all take an optional reverse (default False) parameter that gives the list reversed order resp. iterates in reverse (the non-iterator can also be done relatively efficient with e.g. od.dict().reverse() )
• .update(): takes an optional relax=True which allows one time ordereddict update from normal dictionaries regardless of initialisation time relax setting.

In addition to that ordereddict and sorteddict have some extra methods:

• .index(key) - gives an integer value that is the index of the key
• .setkeys()/.setvalues()/.setitems(), work like those in the Larosa/Foord implementation, although they might throw different exceptions: - setvalues' argument must be an itereable that returns the same number of items as the length of the ordereddict - setitems' argument is free in length, it performs a clear and adds the items in order.
• slice retrieval for all

and ordereddict only also has:

• .setkeys(), works like the one in the Larosa/Foord implementation. Argument must be an itereable returning a permutation of the existing keys ( that implies having the same length as the ordereddict)
• .reverse() - reverses the keys in place
• .insert(position, key, value) - this will put a key at a particular position so that afterwards .index(key) == position, if the key was already there the original position (and value) is lost to the new position. This often means moving keys to new positions!
• slice deletion/assignment:
• stepped deletion could be optimized a bit (individual items are deleted which can require memmoving multiple items)
• assignment only from OrderedDict (with the same length as the slice). This could also be optimised as I first delete, then insert individual items. If the assigned items contain keys that are still there after the deletion 'phase' then retrieving that slice does not always give the original assigned ordereddict (depending on the position of the items with those keys in either ordereddict)
• .rename(oldkey, newkey) renames a key, but keeps the items position and value

## The new OrderedDict in the standard collections module

With Python 3.1 and backported to 2.7 there is an OrderedDict class available in the collections modules. Raymond Hettinger indicated in 2009 at EuroPython that he preferred to start from a minimal OrderedDict instead of using the Larosa/Foord implementation. Unfortunately the available tests (for the functionality that the simple collections.OrderedDict supports) were not used either resulting in preventable bugs like repr initially not working on recursive OrderedDicts.

ordereddict (and the Larosa/Foord implementation) is essentially a superset of collections.OrderedDict, but there are a few differences:

• OrderedDict is by default relax-ed.
• repr of recursive OrderedDict does not give any indication of the value of the recursive key, as it only displays .... ordereddict displays ordereddict([...]) as value. Just using the dots like OrderedDict does is going to be ambiguous as soon as you have two different types A and B and nest A in B in A or B in B in A.
• some newer build-in functions available in OrderedDict are not available in ordereddict ( __reversed__, viewkeys, viewvalues, viewitems).

All of the differences can be straightened out in small (70 lines of Python) OrderedDict wrapper around ordereddict. With this wrapper the OrderedDict tests in the standard test_collections.py all pass.

## Testing

testordereddict.py in the test subdirectory has been used to test the module. You can use:

python testordereddict


to run the tests (py.test support has been dropped as newer versions of py.test were not compatible).

There is a somewhat patched copy of the python lib/Test dictionary testing routines included as well, it fails on the _update test however because the default is not to use a relaxed ordereddict. You can run it with:

cd test/unit
python test_dict.py


## To Do

• implement Value Sorted Order (VSO: specify value=True for normal value comparison), or a value rewrite function for VSO ( e.g. value=string.lower )
• implement Item Sorted Order (ISO): compare value then key ( the other way around would not make sense with unique keys, but we might have non-unique values).
• implement slice deletion for sorteddict
• more testing of sorteddict functionality
• speedtest slices
• speedtest sorteddict
• check on the test_update unittest in test_dict.py

## To Consider

• comparing ordereddicts (as per Larosa/Foord)
• implement the whole (optionally) using pointers in the DictObject Items (Faster on insertion/deletion, slower on accessing slices, makes implementing algorithms somewhat more difficult), would have to seperate code for sorteddict as key position determination would be much slower.
• supply a pure Python implementation of exactly the functionality in ordereddict
• test on older versions (< 2.4) of Python and make portable (if this can be done without too much clutter) or port.
• test on the Mac
• optimise searching for an item pointer for sorteddict with binary search (for deletion)

## Background information

ordereddict is directly derived from Python's own dictobject.c file. The extensions and the representation of ordereddicts() are based on Larosa/Foord's excellent pure Python OrderedDict() module (http://www.voidspace.org.uk/python/odict.html).

The implemenation adds a vector of pointers to elements to the basic dictionary structure and keeps this vector compact (and in order) so indexing is fast. The elements do not know about their position (so nothing needs to be updated there if that position changes, but then finding an item's index is expensive. Insertion/deletion is also relatively expensive in that on average half of the vector of pointers needs to be memmove-d one position. There is also a long value for bit info like kvio, relaxed.

The sorteddict structure has an additional 3 pointers of which only one (sd_key) is currently used (the others are sd_cmp and sd_value).

## Speed

Based on some tests with best of 10 iterations of 10000 iterations of various functions under Ubuntu 7.10 (see test/timeordereddict.py and test/ta.py):

Results in seconds:

-------------------------------   dict         ordereddict  Larosa/Ford  collections
OrderedDict  OrderedDict
empty                             0.023        0.025        0.023        0.024
create_empty                      0.028        0.031        0.147        0.329
create_five_entry                 0.037        0.042        0.384        0.558
create_26_entry                   0.187        0.203        1.494        1.602
create_676_entry                  5.330        5.574       36.797       34.810
get_keys_from_26_entry            0.209        0.231        1.501        1.762
pop_5_items_26_entry              0.219        0.247        1.952        1.864
pop_26_items_676_entry            7.550        8.127       46.578       41.851
popitem_last_26_entry             0.203        0.225        1.624        1.734
popitem_last_676_entry            5.285        5.534       36.912       34.799
popitem_100_676_entry          --------        5.552       36.577     --------
walk_26_iteritems              --------        0.494        2.792        2.238
-------------------------------   dict         ordereddict  Larosa/Ford  collections
OrderedDict  OrderedDict

empty                             0.930     1.000           0.950        0.966
create_empty                      0.909     1.000           4.728       10.594
create_five_entry                 0.892     1.000           9.201       13.374
create_26_entry                   0.923     1.000           7.368        7.901
create_676_entry                  0.956     1.000           6.601        6.245
get_keys_from_26_entry            0.908     1.000           6.508        7.641
pop_5_items_26_entry              0.888     1.000           7.916        7.559
pop_26_items_676_entry            0.929     1.000           5.732        5.150
popitem_last_26_entry             0.901     1.000           7.222        7.712
popitem_last_676_entry            0.955     1.000           6.670        6.288
popitem_100_676_entry          --------     1.000           6.588     --------
walk_26_iteritems              --------     1.000           5.653        4.532


## Why

Because I am orderly ;-O, and because I use dictionaries to store key/value information read from some text file quite often. Unfortunately comparing those files with diff when written from normal dictionaries often obfucates changes because of the reordering of lines when key/value pairs are added and then written.

I have special routine for YAML files that takes lines like:

- key1: val1
- key2: val3
- key3:
- val3a
- val3b


(i.e. a list of key-value pairs) directly to a single ordered dictionary and back. (I find it kind of strange to finally have a structured, human readeable, format that does not try to preserve the order of key-value pairs so that comparing files is difficult with 'standard' text tools).

## Older versions

http://www.xs4all.nl/~anthon/Python/ordereddict used to be ordereddict's home on the web.

## History

0.4.13: 2017-0723 -

0.4.9  2015-08-10
typos fixed by Gianfranco Costamagna

0.4.8  2015-05-31
dependent on ruamel.base
version number in a single place
using py.test under tox
generate wheel for 32/64bit py26/py27 on windows

0.4.6  2014-01-18
Move to ruamel namespace, hosted on bitbucket, MIT License
Testing with tox

0.4.5  2012-06-17
Fix for a bug while inserting last item again beyond last position (reported
by Volkan Çetin / volki tolki ( cetinv at gmail.com )
Fix for repeated deletion and insertion fail. Found by and solution provided
by Darren Dowker (including tests). Also found by Fabio Zadronzy (including
a less elegant fix).
applied reindent to .py and astyle to .c files

0.4.3  2009-05-11
Fix for a bug in slicing SortedDicts.
Found by, and fix provided by, Migel Anguel (linos.es)

0.4.2  2009-03-27
doing deepcopy

0.4.1  2007-11-06
Bug found and fixed by Fabio Zadrozny on resizing dictionaries

0.4   2007-10-30
added KVIO (Key Value Insertion Order ie. key moves to back on update)
implemented sorteddict, with KSO, Key Sorted Order. You can specify
a function for key transformation before comparison (such as string.lower)
sorteddict does not have all of the ordereddict methods as not all make
sense (eg. slice assignment, rename, setkeys)

0.3   2007-10-24
added setkeys/setvalues/setitems; slice retrieval, deletion, assignment
.rename(oldkey, newkey) rename a key keeping same value and position
.index() of non-existing key now returns ValueError instead of SystemError
Changed the module name to _ordereddict (from ordereddict), as Jason
Kirstland probably rightfully suggested that any private implementation
likely has the (file)name ordereddict.py. A modulename with leading
underscore seams more common for extension modules anyway.

0.2a  2007-10-16
Solved the potential GC problem on Windows

0.2   2007-10-16
First release, with some tests, and possible still a GC problem
with Windows.

0.1   2007-10-..
This version was never released. While testing it I was far in writing
an email to comp.lang.python about why timing with timeit did seem to
be memory hungry ....
and then I realised ordereddict had a memory leak %-)