New submission from Eric Snow:
(see issue24667)
collections.OrderedDict subclasses dict so calling dict's methods on an
OrderedDict works. However, neither the pure Python nor the C implementation
of OrderedDict was written to support doing so. In fact, both of them
currently enter an inconsistent state when this happens. For example:
# Python 3.4 (pure Python implementation)
>>> from collections import OrderedDict
>>> od = OrderedDict([('spam', 1), ('eggs', 2)])
>>> dict.__delitem__(od, 'spam')
>>> str(od)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.4/reprlib.py", line 24, in wrapper
result = user_function(self)
File "/usr/lib/python3.4/collections/__init__.py", line 198, in __repr__
return '%s(%r)' % (self.__class__.__name__, list(self.items()))
File "/usr/lib/python3.4/_collections_abc.py", line 485, in __iter__
yield (key, self._mapping[key])
KeyError: 'spam'
# Python 3.5 (C implementation)
>>> from collections import OrderedDict
>>> od = OrderedDict([('spam', 1), ('eggs', 2)])
>>> dict.__delitem__(od, 'spam')
>>> str(od)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'spam'
This is a consequence of subclassing a builtin type, which typically do not
have good support for subclassing (e.g. issue10977).
It probably isn't worth making any changes to the code of either OrderedDict
implementations. At most I'd recommend a note in the OrderedDict documentation
indicating that the results of passing an OrderedDict object to dict.* methods
are undefined.
----------
assignee: docs@python
components: Documentation
messages: 247354
nosy: docs@python, eric.snow, rhettinger
priority: low
severity: normal
status: open
title: The result of calling dict.* methods on OrderedDict is undefined.
type: behavior
versions: Python 2.7, Python 3.4, Python 3.5, Python 3.6
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24721>
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