[issue41409] deque.pop(index) is not supported

[Raymond Hettinger]

Raymond Hettinger <raymond.hettinger at gmail.com> added the comment:

FWIW, the relationship between a concrete class and an ABC is normative with respect to core capabilities but isn't 100% strict.  Concrete classes can vary in small respects when it makes sense.  For example, the __or__ and __and__ methods for collections.Set will accept any iterable, but the concrete does not.  

We use the Liskov substitution principle as a guide, not as a law.  In a number of cases, we choose practicality-beats-purity and allow subclasses to differ in ways than their parents.  Counter() doesn't support fromkeys().  OrderedDict.popitem() has different signature than dict.popitem().

Hope that insight was helpful.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41409>
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