I have the following model
class Window(BaseModel):
size: tuple[int, int]
and I would like to instantiate it like this:
fields = {'size': '1920x1080'}
window = Window(**fields)
Of course this fails since the value of 'size' is not of the correct type. However, I would like to add logic so that the value is split at x, i.e.:
def transform(raw: str) -> tuple[int, int]:
x, y = raw.split('x')
return int(x), int(y)
Does Pydantic support this?
You can implement such a behaviour with pydantic's validator. Given your predefined function:
def transform(raw: str) -> tuple[int, int]:
x, y = raw.split('x')
return int(x), int(y)
You can implement it in your class like this:
from pydantic import BaseModel, validator
class Window(BaseModel):
size: tuple[int, int]
_extract_size = validator('size', pre=True, allow_reuse=True)(transform)
Note the pre=True argument passed to the validator. It means that it will be run before the default validator that checks if size is a tuple.
Now:
fields = {'size': '1920x1080'}
window = Window(**fields)
print(window)
# output: size=(1920, 1080)
Note that after that, you won't be able to instantiate your Window with a tuple for size.
fields2 = {'size': (800, 600)}
window2 = Window(**fields2)
# AttributeError: 'tuple' object has no attribute 'split'
In order to overcome that, you could simply bypass the function if a tuple is passed by altering slightly your code:
def transform(raw: str) -> tuple[int, int]:
if type(raw) == tuple:
return raw
x, y = raw.split('x')
return int(x), int(y)
Which should give:
fields2 = {'size': (800, 600)}
window2 = Window(**fields2)
print(window2)
# output: size:(800, 600)
