Add deque to serialization when Sequence is used as type hinting in V2 #7797
Description
Initial Checks
- I have searched Google & GitHub for similar requests and couldn't find anything
- I have read and followed the docs and still think this feature is missing
Description
It seems like Pydantic V1 had this support, but it was missed on Pydantic V2.
I using Pydantic with project on FastAPI.
In my case I'm working with fast stream of data, so I had to use deque. As for the type hinting I using Sequence[MyModel]
however Pydantic cannot recognize deque as valid Sequence type, even if it is if you check with isinstance(my_deque, Sequence) -> True
When it trying to serialize, it throw error:
Traceback (most recent call last):
File "/usr/local/lib/python3.11/site-packages/starlette/middleware/errors.py", line 162, in __call__
await self.app(scope, receive, _send)
File "/usr/local/lib/python3.11/site-packages/starlette/middleware/cors.py", line 83, in __call__
await self.app(scope, receive, send)
File "/usr/local/lib/python3.11/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
raise exc
File "/usr/local/lib/python3.11/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
await self.app(scope, receive, sender)
File "/usr/local/lib/python3.11/site-packages/fastapi/middleware/asyncexitstack.py", line 20, in __call__
raise e
File "/usr/local/lib/python3.11/site-packages/fastapi/middleware/asyncexitstack.py", line 17, in __call__
await self.app(scope, receive, send)
File "/usr/local/lib/python3.11/site-packages/starlette/routing.py", line 718, in __call__
await route.handle(scope, receive, send)
File "/usr/local/lib/python3.11/site-packages/starlette/routing.py", line 276, in handle
await self.app(scope, receive, send)
File "/usr/local/lib/python3.11/site-packages/starlette/routing.py", line 66, in app
response = await func(request)
^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/fastapi/routing.py", line 291, in app
content = await serialize_response(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/fastapi/routing.py", line 159, in serialize_response
return field.serialize(
^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/fastapi/_compat.py", line 141, in serialize
return self._type_adapter.dump_python(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/pydantic/type_adapter.py", line 266, in dump_python
return self.serializer.to_python(
^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'collections.deque'>Project running in Docker with requirements.txt:
fastapi[all]==0.100.*
pydantic[email]==2.4.*
uvicorn[standard]==0.23.*
(not related requirements are omitted)
2.4.2 is current version
Affected Components
- Compatibility between releases
- Data validation/parsing
- Data serialization -
.model_dump()and.model_dump_json() - JSON Schema
- Dataclasses
- Model Config
- Field Types - adding or changing a particular data type
- Function validation decorator
- Generic Models
- Other Model behaviour -
model_construct(), pickling, private attributes, ORM mode - Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.