DOC: Add NpzFile class documentation.

[liang3zy22]

This PR is to fix #6337. Don't know where to add this documentation as reference. Please give comment.

Closes #6337

[rossbar]

Thanks @liang3zy22 , +1 for adding this. Rather than adding a new section, I'd vote to add lib.npyio.NpzFile to the end of the first autosummary (i.e. after savez_compressed).

[liang3zy22]

NpzFile some methods(get, items, keys, values) don't have description. Do we need to add some docstring for these methods? It seems that these methods need to be overridden.

[rossbar]

NpzFile some methods(get, items, keys, values) don't have description. Do we need to add some docstring for these methods? It seems that these methods need to be overridden.

Those are inherited from the base class - I wouldn't worry about them too much. IMO they're fine as-is (the one-line summary is descriptive enough). If you wanted to try to improve the situation, I'd recommend taking a look a the :no-inherited-members: option for autosummary; and/or the numpydoc_show_inherited_class_members configuration option (i.e. try excluding NpzFile from this listing).

Either way, if you're interested in investigating that let's do so in a follow-up PR so that we don't block this obvious improvement to the docs. Thanks @liang3zy22 !