Using StanFit4Model with Python type hints
rgerkin opened this issue · 3 comments
Summary:
It is unclear how I can provide a "StanFit4Model" type hint.
Description:
Suppose I write a function that takes a fit and does something to it, like compute a single number:
def my_func(fit):
return do_something(fit)
And I would like to provide type hints of the kind supported in Python 3.5 and described in PEP 484.
def my_func(fit: pystan.StanFit4model) -> float:
return do_something(fit)
However, pystan.StanFit4Model (despite being called exactly this in the docs here) is not actually an importable thing. For example, none of these work from a fresh Python kernel:
from pystan import stanfit4model
from pystan.stanfit4model import StanFit4model)
Basically I just want something I can import, given that PyStan is installed, that will work with type hinting, i.e. a SOMETHING I can import for while the following assertion would pass:
assert isinstance(some_fit_instance, SOMETHING)
Reproducible Steps:
Either of the lines will not work from a fresh Python kernel with pystan installed:
from pystan import stanfit4model
from pystan.stanfit4model import StanFit4model
PyStan Version:
2.19.1.1
Python Version:
3.7
Operating System:
Ubuntu
Hi,
Yes, stanfit4model.pyx is a template file that is filled and then compiled to a module at runtime. So it can not be imported from PyStan.
We would need to write .pyi files for our compiled modules (like we are doing for httpstan / pystan3) --> https://github.com/stan-dev/httpstan/tree/master/httpstan
There are couple of options: Either,
extend PyStan2 with a PR (.pyi for the model)
or
use typing.Any and ignore the type. To assert that the type is correct, you can use the same procedure we use in ArviZ --> test against the class name
https://github.com/arviz-devs/arviz/blob/master/arviz/data/converters.py#L79
assert(some_fit_instance.__class__.__name__ == "StanFit4Model")
Oh yeah, I totally forgot that part.