Subclassing StrictStr / ConstrainedStr causes ValidationError

[skewty]

Bug

Please complete:

• OS: Manjaro Linux
• Python version: 3.7.4
• Pydantic version: 1.2.0

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Original bug discussion in #799

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I am sorta lost as to why this isn't working as expected for me in v1.2:

from typing import Type, TypeVar
import pydantic


class ConnectionName(pydantic.StrictStr):
    min_length = 1


class EndpointStr(pydantic.StrictStr):
    min_length = 1


DEFAULT_ENDPOINT = EndpointStr("default")
T = TypeVar("T", bound="UpRequestEvent")


class UpRequestEvent(pydantic.BaseModel):
    connection_name: ConnectionName  # connection name
    connection_endpoint: EndpointStr  # connection name's endpoint (for server type connections)

    @classmethod
    def build_from(
        cls: Type[T],
        connection_name: ConnectionName,
        connection_endpoint: EndpointStr = DEFAULT_ENDPOINT,
        **kwargs
    ) -> T:
        return cls(
            connection_name=connection_name,
            connection_endpoint=connection_endpoint,
        )

    class Config:
        use_enum_values = True


# This works
UpRequestEvent.build_from(
    connection_name="test", connection_endpoint="default",
)

# This fails
UpRequestEvent.build_from(
    connection_name=ConnectionName("test"), connection_endpoint=EndpointStr("default"),
)

Traceback (most recent call last):
  File "/opt/pycharm-eap/plugins/python/helpers/pydev/pydevd.py", line 1415, in _exec
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "/opt/pycharm-eap/plugins/python/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/home/spalmer1009/.PyCharm2019.3/config/scratches/scratch.py", line 44, in <module>
    connection_name=ConnectionName("test"), connection_endpoint=EndpointStr("default"),
  File "/home/spalmer1009/.PyCharm2019.3/config/scratches/scratch.py", line 30, in build_from
    connection_endpoint=connection_endpoint,
  File "pydantic/main.py", line 274, in pydantic.main.BaseModel.__init__
pydantic.error_wrappers.ValidationError: 2 validation errors for UpRequestEvent
connection_name
  Expected unicode, got ConnectionName (type=type_error)
connection_endpoint
  Expected unicode, got EndpointStr (type=type_error)

My special types ConnectionName and EndpointStr are a subclass of str (through StrictStr -> ConstrainedStr)

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As discovered by @dmontagu the issue only seems to exist when the code is Cython compiled.