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Decimal is a custom type #848
Description
Hey!
I have a problem when I use msgspec and Decimal. One popular solution to using Decimal is to not round the data as part of the algorithm execution and domain layer. The rounding happens during demarshaling at the API endpoints. Decimal is the native type, so it's not possible to create an Encoder that can handle this.
Is it possible to change the behaviour for Decimal and allow interception in enc_hook?
Example:
from decimal import ROUND_HALF_UP, Decimal
from typing import Any
import msgspec
def enc_hook(obj: Any) -> Any:
if isinstance(obj, Decimal):
return str(obj.quantize(Decimal("0.0001"), rounding=ROUND_HALF_UP))
else:
raise NotImplementedError(f"Objects of type {type(obj)} are not supported")
class Price(msgspec.Struct):
primecost: Decimal
enc = msgspec.json.Encoder(enc_hook=enc_hook)
price = Price(primecost=Decimal("1.1234444"))
buf = enc.encode(price)
# b'{"primecost":"1.1234"}'Creating a custom Decimal MyDecimal looks like a workaround.
Reacted by 叶子
Activity
[-]Decimal should be handled as a custom type during demarshaling.[/-][+]Decimal is a custom type[/+][-]Decimal is a custom type[/-][+]`Decimal` is a custom type[/+]JimDabell commentedon Aug 4, 2025
See also #829 and #849.
Add callable support for `decimal_format` option (msgspec#978)