Make Dict a mutable mapping

[sphuber]

Potential methods, we might want to implement:

• clear
• get
• items
• keys
• pop
• popitem
• setdefault
• update
• values
• __getitem__
• __setitem__
• __delitem__
• __getattr__
• __setattr__
• __delattr__

[zhubonan]

This would be convenient. At the moment I have to write extra lines to create a dict from Dict, update and save it back.

[sphuber]

Note that the mutable methods will not work for a stored node, however. Or we might decide that when that is the case, a normal dict is made out of the stored node, the method is applied on that object and then returned. But this kind of magic may be too counter-intuitive and too dangerous.

[mbercx]

@sphuber found this old issue when looking for issues related to #5970. Something to consider if/when we try to fix that.