Cython implementation of OrderedDict
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python2/cyordereddict Remove fake __dict__ to fix pickling issue Dec 7, 2014
.gitignore dual python2/3 packaging Nov 12, 2014
.travis.yml Fix test suite Feb 5, 2016
LICENSE.txt Updated manifest and travis Nov 12, 2014
README.rst Fix test suite Feb 5, 2016


This library is obsolete! Python 3.5's collections.OrderedDict was rewritten in C, and is now significantly faster than cyordereddict.OrderedDict for almost all operations.


The Python standard library's OrderedDict ported to Cython. A drop-in replacement that is 2-6x faster.

pip install cyordereddict
CPython (2.6, 2.7, 3.3 or 3.4) and a C compiler. Cython is only required for the dev version.
from cyordereddict import OrderedDict

Python 2.7:

Test Code Ratio (stdlib / cython)
__init__ empty OrderedDict() 1.8
__init__ list OrderedDict(list_data) 4.8
__init__ dict OrderedDict(dict_data) 4.6
__setitem__ ordereddict[0] = 0 8.6
__getitem__ ordereddict[0] 3
update ordereddict.update(dict_data) 5.5
__iter__ list(ordereddict) 5.6
items ordereddict.items() 5.9
__contains__ 0 in ordereddict 2.3

Python 3.4:

Test Code Ratio (stdlib / cython)
__init__ empty OrderedDict() 1.5
__init__ list OrderedDict(list_data) 3.9
__init__ dict OrderedDict(dict_data) 4.2
__setitem__ ordereddict[0] = 0 8.4
__getitem__ ordereddict[0] 2.9
update ordereddict.update(dict_data) 6.5
__iter__ list(ordereddict) 2.3
items list(ordereddict.items()) 2.1
__contains__ 0 in ordereddict 2.3

To run these yourself, use cyordereddict.benchmark()


cyorderedddict.OrderedDict is an extension type (similar to the built-in dict) instead of a Python class. This is necessary for speed, but means that in a few pathological cases its behavior will differ from collections.OrderedDict:

  • The inspect module does not work on cyorderedddict.OrderedDict methods.
  • Extension types use slots instead of dictionaries, so you cannot add custom attributes without making a subclass (e.g., = 'bar' will fail).

You can do anything else you might do with an OrderedDict, including subclassing: everything else passes the collections.OrderedDict test suite. We based the Cython code directly on the Python standard library, and thus use separate code bases for Python 2 and 3, specifically to reduce the potential for introducing new bugs or performance regressions.

MIT. Based on the Python standard library, which is under the Python Software Foundation License.