<div dir="ltr">* DOC: OrderDict.values() comparisons in Python 3<div><div> * Src: <a href="https://hg.python.org/cpython/file/f2a0a4a45292/Doc/library/collections.rst#l793">https://hg.python.org/cpython/file/f2a0a4a45292/Doc/library/collections.rst#l793</a><br></div></div><div><br></div><div>What should it say?</div><div><br></div><div><div>```rst</div><div><br></div><div>.. `<<a href="https://hg.python.org/cpython/file/f2a0a4a45292/Doc/library/collections.rst#l793">https://hg.python.org/cpython/file/f2a0a4a45292/Doc/library/collections.rst#l793</a>>`__</div><div><br></div><div>collections.OrderedDict.values().__eq__</div><div><br></div><div>* "is suprising"</div><div>* Python 3 has `dict views`_</div><div><br></div><div>* :class:`OrderedDict` matches the dict interface in Python 2.7 and</div><div> Python 3.</div><div> * <a href="https://docs.python.org/2/library/collections.html#collections.OrderedDict">https://docs.python.org/2/library/collections.html#collections.OrderedDict</a></div><div> * <a href="https://docs.python.org/3/library/collections.html#collections.OrderedDict">https://docs.python.org/3/library/collections.html#collections.OrderedDict</a></div><div><br></div><div>* Python 2 dict interface:</div><div> * dict.viewkeys(), dict.viewvalues(), dict.viewitems()</div><div> * dict.keys(), dict.values(), dict.items()</div><div> * <a href="https://docs.python.org/2/library/stdtypes.html#dict">https://docs.python.org/2/library/stdtypes.html#dict</a></div><div> * <a href="https://docs.python.org/2/library/stdtypes.html#dict.values">https://docs.python.org/2/library/stdtypes.html#dict.values</a></div><div> * <a href="https://docs.python.org/2/library/stdtypes.html#dictionary-view-objects">https://docs.python.org/2/library/stdtypes.html#dictionary-view-objects</a></div><div>* Python 3 dict interface (:ref:`dictionary view objects`:</div><div> * dict.keys(), dict.values(), dict.items()</div><div> * list(dict.keys()), list(dict.values()), list(dict.items())</div><div> * <a href="https://docs.python.org/3/library/stdtypes.html#dict">https://docs.python.org/3/library/stdtypes.html#dict</a></div><div> * <a href="https://docs.python.org/3/library/stdtypes.html#dict.values">https://docs.python.org/3/library/stdtypes.html#dict.values</a></div><div> * <a href="https://docs.python.org/3/library/stdtypes.html#dictionary-view-objects">https://docs.python.org/3/library/stdtypes.html#dictionary-view-objects</a></div><div><br></div><div><br></div><div>* In order to compare OrderedDict.values() **by value**</div><div> you must either:</div><div> </div><div> * Cast values() to a sequence (e.g. a list) before comparison</div><div> * Subclass :class:`OrderedDict` and wrap `values()`</div><div><br></div><div><br></div><div>.. code:: python</div><div><br></div><div> from collections import OrderedDict</div><div> a = 'a'</div><div> x = 1</div><div> y = x</div><div> ab = [( a, x), ('b', 2)]</div><div> ba = [('b', 2), (a, y)]</div><div> ab_odict = OrderedDict(ab)</div><div> ab_odict_ = OrderedDict(ab)</div><div> ab_odict_copy = OrderedDict(ab.copy())</div><div> ba_odict = OrderedDict(ba)</div><div> ab_dict = dict(ab)</div><div> ba_dict = dict(ba)</div><div><br></div><div> # In Python 3,</div><div> # OrderedDict.values.__eq__ does not compare by value:</div><div> assert ( ab_odict.values() == ab_odict_.values()) is False</div><div> assert (list(ab_odict.values()) == list(ab_odict_.values()) is True</div><div><br></div><div> # In Python 2.7 and 3,</div><div> # OrderedDict.__eq__ compares ordered sequences</div><div> assert (ab_odict == ab_odict_) is True</div><div> assert (ab_odict == ab_odict_copy) is True</div><div> assert (ab_odict == ba_odict) is False</div><div> assert (ab_dict == ba_dict) is True</div><div> </div><div><br></div><div> # - [ ] How to explain the x, y part?</div><div> # - in terms of references, __eq__, id(obj), __hash__</div><div><br></div></div><div>```</div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jan 20, 2016 at 12:39 PM, Sven R. Kunze <span dir="ltr"><<a href="mailto:srkunze@mail.de" target="_blank">srkunze@mail.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
Documentation is a very good idea.<br>
<br>
Maybe, even raise an error when comparing values.<br>
<br>
Best,<br>
Sven<div><div class="h5"><br>
<br>
<div>On 20.01.2016 12:13, Alexandre Figura
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div>
<div>If we put technical considerations aside, maybe we
should just ask to ourselves what behavior do we expect
when doing equality tests between ordered dictionaries. As
a reminder:<br>
<br>
>>> xy = OrderedDict([('x', None), ('y', None)])<br>
>>> yx = OrderedDict([('y', None), ('x', None)])<br>
>>> xy == yx<br>
False<br>
>>> xy.items() == yx.items()<br>
True<br>
>>> xy.keys() == yx.keys()<br>
True<br>
>>> xy.values() == yx.values()<br>
False<br>
<br>
So, it appears that:<br>
1. equality tests between odict_values use objects
identity and not equality,<br>
</div>
2. equality tests between odict_keys do not respect order.<br>
<br>
</div>
If it is not technically possible to change the current
implementation, maybe all we can do is just add a warning
about current behavior in the documentation?<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Jan 11, 2016 at 4:17 AM,
Guido van Rossum <span dir="ltr"><<a href="mailto:guido@python.org" target="_blank"></a><a href="mailto:guido@python.org" target="_blank">guido@python.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Seems like we dropped the ball... Is there
any action item here?<span><br clear="all">
<div class="gmail_extra"><br>
-- <br>
<div>--Guido van Rossum (<a href="http://python.org/%7Eguido" target="_blank">python.org/~guido</a>)</div>
</div>
</span></div>
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