andy-maier / immutable-views Goto Github PK

This would be for encoding DictView and ListView objects into JSON.
For decoding, this would probably not be interesting.

In case the view classes are used on hashable collections (e.g. frozenset, any of the immutable collection classes on Pypi, nocasedict with the limited hashing support, etc), they should support the __hash__() method and delegate that to the underlying collection, leaving it to that collection to reject the call.

Also, test code should be added that verifies the rejection for non-hashable underlying collections and the success for hashable underlying collections.

Finally, this topic deserves a short section in the docs.

Places in test code that access protected attributes of the View objects:

TBD: What about test DictView()?
test_dict_view.py:1496/1501 - test DictView.copy()
test_list_view.py:230/238 - test ListView()
test_list_view.py:1782/1787 - test ListView.copy()
test_set_view.py:203/210 - test SetView()
test_set_view.py:3334/3339 - test SetView.copy()

This is a copy&paste error and needs to be fixed.

In Python 3.9, two new operator methods have been added to ´dict`:

• def __or__(self) - used in self | other
• def __ior__(self)- used in self |= other

PR #9 implements SetView, but tests still need to be written.

Some facts on types.MappingProxyType (as of Python 3.9):

• probably a bug: permits initialization with a string (opened https://bugs.python.org/issue43828, closed without resolving it, based on compatibility considerations)
• is not hashable, even if the underlying mapping is hashable (opened https://bugs.python.org/issue43829)
• cannot be pickled (see https://bugs.python.org/issue31209, closed without adding it)
• is not serializable to JSON (see https://bugs.python.org/issue34858)

SetView and ListView already has them.

I really like the idea of this library. I could not find any other libraries that provide the same functionality, and I think this is a valuable and somehow unused contribution to the community. However, to provide the same user experience as if using the collections themselves, I think type annotations should be provided. I will try and pick that up, and, if welcome, make a PR some time later.

Class DictView currently inherits from abstract class Mapping, but implements the read-only functions of dict which provides some more functions than those of Mapping, so inheriting from dict would be nice, also from a perspective that this would allow using DictView objects where dict objects are declared and checked. On the other hand, DictView does not implement the modifying methods of dict, and inheriting from dict is a statement that it does support all of its methods.

Ditto for ListView, it implements read-only methods from list but inherits from Sequence.

Clarify whether the inheritance should be changed.

Asked the question on the python-list mailing list: https://mail.python.org/pipermail/python-list/2021-April/901876.html

The SetView class has the latest level of documentation.
Update the documentation of the ListView and DictView classes to match that of SetView.