Predictor objects do not serialize output transforms

[canerturkmen]

Description

Representable predictor objects do not serialize/deserialize the output transformation. See here. This prevents consistent serde as well as the ability to reuse existing predictor objects. Also see the discussion in #1458 .

[lostella]

Would this be just as easy as it's done here?

[canerturkmen]

that doesn't appear to be the case. In general output transforms are just Callables. For a simple function I get:

RuntimeError: Cannot serialize type builtins.function.

[lostella]

Yeah that’s an issue of course. In my opinion it should be fine to use whatever callable objects wherever they fit, as long as you’re willing to pay the price that it may not be serializable nicely. We could use for output transforms similar things like we use for the input, right? And have serialization rely on the @validated decorator

[canerturkmen]

OutputTransform is currently an alias for a certain Callable interface. It could become a serializable object of its own although seeing as it doesn't look like it's being used much I'm not sure if it's worth the effort.

[lostella]

It could become a serializable object of its own although seeing as it doesn't look like it's being used much I'm not sure if it's worth the effort.

What I mean is that one does not need to do much, in order to provide an object compatible with dump_json: just extend OutputTransform (to make type checking happy) and decorate the constructor:

In [11]: class MyOutputTransform(OutputTransform):
    ...:     @validated()
    ...:     def __init__(self, coeff: float):
    ...:         self.coeff = coeff
    ...:     def __call__(self, entry, x):
    ...:         return entry["target"] + coeff*x
    ...:

In [12]:

In [12]:

In [12]: output_transform = MyOutputTransform(42.0)

In [13]: encode(output_transform)
Out[13]:
{'__kind__': <Kind.Instance: 'instance'>,
 'class': '__main__.MyOutputTransform',
 'args': [],
 'kwargs': {'coeff': 42.0}}

In [14]: decode(encode(output_transform))
Out[14]: __main__.MyOutputTransform(coeff=42.0)

(These encode/decode functions are what is used internally for serde from/to json)