`dict` property

[fwkoch]

Another possibly useful builtin property? I've used Instance properties with instance_class=dict quite a bit. Could be interesting to provide some validation on keys/values?

[bsmithyman]

Yeah, I've wondered about that. I guess I've tended to build up sub-HasProperties classes and then tied instances to those, but there are going to be times when it is useful to have the flexibility of a dict. I confess, it never really occurred to me to use dict with Instance, and I wonder if that is sufficient. What sort of validation are you thinking of?

Edit: i.e., I wonder if it is sufficient to have a dict instance example in the docs?

[fwkoch]

In cases where a dictionary has known set of keys, it makes sense to use another HasProperties instance, but for arbitrary keys, this doesn't work. It is certainly possible to just use an Instance property with instance_class=dict.

One advantage of a new property type is added validation on keys and values. An example that comes to mind - thinking along the lines of schema generation, you could do something like:

class MySchema(properties.HasProperties):

    paths = properties.Dict(
        doc='Available paths and their methods',
        key_prop=properties.String('', regex='^/'),
        value_prop=properties.Instance('', SwaggerPathSpec),
    )

A few other advantages

• slightly less verbose do use Dict rather than Instance of dict (not that big of a deal)
• allows us to observe_mutations (ie my_dict.update(...) fires change notifications) (also probably not that big of a deal...)

Initial implementation is here https://github.com/3ptscience/properties/blob/feat/dict_prop/properties/base/containers.py - still needs some work and further discussion.

[lheagy]

A quick note to say +1 on a Dictionary (or Dict) property!

[bsmithyman]

@lheagy
Yeah, we need to get this in: #188

[fwkoch]

#188 merged!