[python-experimental] implement in operator for model classes

[mks-m]

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Allow to check for attribute presence in model using in operator.

Unless I'm missing something, right now the only way to correctly get an attribute which may not be present is this:

try:
    attr_value = instance.attr_name
except ApiAttributeError:
    attr_value = None

which is quite cumbersome.

@spacether

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[spacether]

Thank you for the PR. This looks great!

[mks-m]

@spacether relevant question - is there value in raising an exception instead of returning None for access of legit attribute that doesn't have value? now that it's possible to test for presence of an attribute, it's easy to differentiate between that and legit None value.

code i want to simplify is this:

value = instance.attr if 'attr' in instance else None
if value is not None:
    # do something

with default None it's just be:

if instance.attr is not None:
    # do something

thoughts?

[spacether]

In my opinion there is value. Attributes can be nullable which is different than being unset.
Let's say
attribute_a has value None if we access it we should get None
Now let's say attribute a is unset if we try to access it directly with model.attribute_a we should get some kind of exception. This lets us differentiate between these use cases.

[spacether]

If you want this functionality why not add a default missing input argument to a get method in ModelNormal and ModelComposd? That would make it work like python dict.get.
Then one could do model.get(param_name, default_value_if_missing)
Also though, what if I want a property named get? How would we support that use case?

Why not use model._data_store.get(name)?

[mks-m]

Now let's say attribute a is unset if we try to access it directly with model.attribute_a we should get some kind of exception. This lets us differentiate between these use cases.

we definitely can differentiate in both cases via exception or by using 'attr' in instance, i just think that using exceptions for that leads to more complex code than necessary. it is much more often that one needs to react to None value regardless if it was set or the attribute is missing, than to differentiate between set and unset None.

Then one could do model.get(param_name, default_value_if_missing)

yes, that's another method i want to add, but it would be nice if using attributes directly was more convenient. right now i have to wrap in try/except way too much :(

Why not use model._data_store.get(name)?

i don't think all attributes are in there? required attributes seem to be in model.__dict__ directly.

[spacether]

i don't think all attributes are in there? required attributes seem to be in model.dict directly.

The attribute that are not in _data_store are data about the class or the composed instance.
I think that all payload key value pairs are in _data_store.