[Feature Request] Support (str, Enum) like StrEnum

[sayevsky]

What are you really trying to do?

I'm trying to use enum class to pass it to activity as an input.

Describe the bug

Activity deserializes bytes to list of chars instead of given Enum

Minimal Reproduction

from enum import Enum

from temporalio.api.common.v1.message_pb2 import Payload
from temporalio.converter import JSONPlainPayloadConverter

class SomeEnum(str, Enum):
    ONE = "one"
    TWO = "two"



converter = JSONPlainPayloadConverter()
result = converter.from_payload(Payload(metadata={
    "key": b"encoding",
    "value": b"json/plain"},
    data=b"\"one\""),
    SomeEnum)
print(result)

Output:

['o', 'n', 'e']

Environment/Versions

• OS and processor: [e.g. M1 Mac, x86 Windows, Linux]
• M1 Mac, though any architecture impacted
• Temporal Version: [e.g. 1.14.0?] and/or SDK version
  SDK version is 1.6.0
• Are you using Docker or Kubernetes or building Temporal from source?
  No

Additional context

JSONPlainPayloadConverter deserializes IntEnum, StrEnum correctly, but it is more reliable to convert payload to any Enum

[cretz]

Per https://github.com/temporalio/sdk-python?tab=readme-ov-file#data-conversion and https://docs.temporal.io/develop/python/converters-and-encryption#payload-conversion, only StrEnum and IntEnum are supported directly. Can you extend from one of those?

[sayevsky]

Hello, @cretz, thank you for the quick follow up.
Is the decision by not supporting basic Enum intentional? Are there any known corner-cases that stop adding additional functionality?

I can extend, but it is seems, that I need to copy-paste the whole value_to_type into my project. That is because types could be generic and value_to_type traverse the type recursively.

[sayevsky]

As proposal:

...
# StrEnum, available in 3.11+
    if sys.version_info >= (3, 11):
        if inspect.isclass(hint) and issubclass(hint, StrEnum):
            if not isinstance(value, str):
                raise TypeError(
                    f"Cannot convert to enum {hint}, value not a string, value is {type(value)}"
                )
            return hint(value)
# proposal to add the code:
    if inspect.isclass(hint) and issubclass(hint, Enum):
        if not isinstance(value, str):
            raise TypeError(
                f"Cannot convert to enum {hint}, value not a string, value is {type(value)}"
            )
        return hint(value)

[cretz]

Is the decision by not supporting basic Enum intentional?

It is because there is no clear serialization of plain Enum. But there is for (str, Enum) together so we can probably support that combo (though we, and Python, suggest using StrEnum now if you can). Your proposal is close, but we probably also need to also check that it's a subclass of both str and Enum and not just Enum. We'll look into adding this, thanks!

[sayevsky]

Similar enhancement for (int, Enum) would be nice. And if both checks do not match, then throw Exception. Because current behaviour is not obvious.

Thanks.