New submission from Kevin Shweh:
The only check that prevents instantiating abstract classes is in
object.__new__, but most built-in classes never actually call object.__new__.
That means you can do stuff like
import abc
class Foo(list, metaclass=abc.ABCMeta):
@abc.abstractmethod
def abstract(self):
pass
Foo()
and the Foo() call will silently succeed.
Ideally, the Foo() call should fail. Other options include having the Foo class
definition itself fail, or just making a note in the documentation describing
the limitation. (As far as I can see, this is currently undocumented.)
----------
assignee: docs@python
components: Documentation, Library (Lib)
messages: 299810
nosy: Kevin Shweh, docs@python
priority: normal
severity: normal
status: open
title: Abstract classes derived from built-in classes don't block instance
creation
type: behavior
versions: Python 2.7, Python 3.6
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Python tracker <[email protected]>
<http://bugs.python.org/issue31127>
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