Brings in:
- re-usable `SerialisedModel`
- speed improvements to processing CSVs against email templates
I chose not to rename `JSONModel` or `ModelList` to keep the diff nice
and small.
`dir(object)` is a useful Python function that tells you what attributes
and methods an object has. It’s also used by tools like iPython and IDEs
for code completion.
Some of the attributes of a `JSONModel` are dynamic, based on what
fields we expect in the underlying JSON. Therefore they don’t
automatically end up in the result of calling `dir`. To get around this
we can implement our own `__dir__` method, which also returns the names
of the fields we’re expecting the the JSON.
Inspired by this Raymond Hettinger tweet:
> #python tip: If you add attributes to an API with __getattr__() or
> __getattribute__(), remember to update __dir__() to make the extension
> introspectable.
— https://twitter.com/raymondh/status/1249860863525146624
`__getattr__` is called whenever an attribute error is raised.
This means that if something deep inside a property on a model raised
an attribute error, that error would be caught by `__getattr__`, which
would then raise an exception that looked like the property itself
didn’t exist. Very confusing.
The solution seems to be to override `__getattribute__` instead, which
handles _all_ attributes, not just those that aren’t explicitly defined.
We then only intervene if the desired attribute is one of the
`ALLOWED_PROPERTIES`, otherwise falling through to the built in methods
of the underlying `object`.
