Validator on dataclasses
I recently stumble upon the need for validator on dataclasses, and had a look at the doc, which specify to create an issue for it, so here I am :-)
Here is my usecase :
#!/usr/bin/env python
# -*- coding: utf-8 -*-
from __future__ import annotations
from pydantic import validator
from pydantic.dataclasses import dataclass
import typing
import mpmath
class PydanticConfig:
arbitrary_types_allowed = True
class BoundedPriceError(Exception):
pass
@dataclass(frozen=True, config=PydanticConfig)
class BoundedPrice:
"""
Class representing a price interval
"""
value: mpmath.mp.mpf
# delegating implementation to mpmath
bounds: mpmath.iv.mpf
@validator('value')
def value_init(self, v: float):
return mpmath.mp.mpf(v)
@validator('bounds')
def bounds_init(self, i: typing.Iterable):
return mpmath.iv.mpf(i)
def __post_init__(self):
# checking bounds right after init, to except early.
self()
def __call__(self) -> mpmath.mp.mpf:
"""
Calling this instance verify the bounds and return the actual value
:return:
"""
try:
self.value in self.bounds
except Exception as exc:
raise BoundedPriceError("Price value not inside bounds", original=exc)
return self.value
if __name__ == "__main__":
p = BoundedPrice(value=34.56, bounds=[33.5, 35.7])
assert type(p) is BoundedPrice
print(p)
I had to specifically allow arbitrary types, given how mpmath does his types dynamically (based on the context).
Then I want to use the constructors from mpmath, to rely on its implementation there, and validate the values based on that.
I use a dataclass mostly because it is a convenient way to hold data, and provide useful functions out of the box, and I could eventually extend this dataclass to support basic arithmetic...
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