serde transparently

[uyha]

After #255, type checking for deserialization is declared at the type level, not at deserialization invocation anymore, this leads to having no way to do type checking at a snippet like this (I actually have problem with msgpack, but I use JSON since it's more popular):

from serde.json import from_json, to_json


int_json = to_json(1)
string_json = to_json("1")

print(f"{int_json=} {string_json=}")
print(f"{from_json(str, int_json)=} {from_json(int, string_json)=}")

One solution I'd like to propose is to have a transparent attribute, similar to what the Rust crate serde has (transparent) which allows creating wrapper around a type without requiring using the target format's container type. So we'd have something like

from serde import serde, Strict
from serde.json import from_json, to_json

@serde(transparent=True, type_check=Strict)
class StrictString:
    value: str

int_json = to_json(1)
string_json = to_json("1")

from_json(str, string_json) # returns a normal str
from_json(StrictString, string_json) # returns a StrictString with value being "1"
from_json(StrictString, int_json) # raises SerdeError

[yukinarit]

Hi @uyha
Thanks for a proposal with good example! Yeah, It's nice to have transparent feature.

Right now, I am working on a pretty big change #237 right now (branch). I can take a look at this after that. Or If you're interested in contributing to pyserde, I am happy to assist you.

[yukinarit]

Awesome!

I think the implementation will be similar to flatten feature.
you can find code serializing and serializing flatten here

• Serialize:

  pyserde/serde/se.py

  Lines 815 to 820 in 03c0c1f

  	if arg.flatten:
  	flattened = []
  	for f in sefields(arg.type, self.serialize_class_var):
  	f.parent = arg # type: ignore
  	flattened.append(self.render(f))
  	return ", ".join(flattened)

• Deserialize:

  pyserde/serde/de.py

  Lines 819 to 827 in 03c0c1f

  	else:
  	# Because the field is flattened
  	# e.g. "data" will be used as variable name.
  	assert arg.datavar
  	if arg.iterbased:
  	var = f"{arg.datavar}[{arg.index}:]"
  	else:
  	var = arg.datavar

It's good to know how to see the generated code by

python -m serde.insepct {source} {class}

e.g. To see generated code for flatten example.

python -m serde.inspect examples/flatten.py Foo
 

[uyha]

sorry, I was using my work account to comment, so I removed that, I'll still keep working on a PR though.