[issue9823] OrderedDict is comparable to dict

[Raymond Hettinger]

Raymond Hettinger <rhettinger at users.sourceforge.net> added the comment:

That is the documented and tested behavior:  http://docs.python.org/library/collections.html#ordereddict-objects

"""
Equality tests between OrderedDict objects are order-sensitive and are implemented as list(od1.items())==list(od2.items()). Equality tests between OrderedDict objects and other Mapping objects are order-insensitive like regular dictionaries. This allows OrderedDict objects to be substituted anywhere a regular dictionary is used.
"""

It was a basic design objective for OrderedDicts to be substitutable for regular dictionaries (that is why it subclasses from dict).  This lets an OD be used just about anywhere in Python where a regular dict is expected.

Also look at:  http://en.wikipedia.org/wiki/Liskov_substitution_principle

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assignee:  -> rhettinger
nosy: +rhettinger

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