rpgoldman · May 3, 2024 20:53 · May 3, 2024
diff --git a/mypy-output.txt b/mypy-output.txt
@@ -0,0 +1,3 @@
+dspy/signatures/mypy_issue.py:35: error: Too many arguments for "Signature"  [call-arg]
+dspy/signatures/mypy_issue.py:35: error: Incompatible return value type (got "Signature", expected "type[Signature]")  [return-value]
+Found 2 errors in 1 file (checked 1 source file)
diff --git a/mypy_issue.py b/mypy_issue.py
@@ -0,0 +1,40 @@
+import typing
+from typing import Union, Type, Optional
+import pydantic.fields
+from pydantic import BaseModel, Field, create_model
+from pydantic.fields import FieldInfo
+
+import dsp
+from dspy.signatures.field import InputField, OutputField, new_to_old_field
+
+# I don't love this, but mypy cannot deal with the dynamic lookup of this metaclass - rpg
+PydanticMetaClass: typing.TypeAlias = pydantic._internal._model_construction.ModelMetaclass
+
+assert PydanticMetaClass == type(pydantic.BaseModel), \
+    "Implementation of Signature MetaClass depends on the internals of Pydantic, which have changed."
+
+
+class SignatureMeta(PydanticMetaClass):
+    pass
+
+
+class Signature(BaseModel, metaclass=SignatureMeta):
+    """"""  # noqa: D419
+    pass
+
+
+# example usages
+
+def ensure_signature(
+        signature: Union[str, Type[Signature]], instructions: Optional[str] = None
+) -> Type[Signature]:
+    if signature is None:
+        raise ValueError("Signature argument is mandatory")
+    if isinstance(signature, str):
+        # FIXME: According to mypy, Signature cannot be called with 2 arguments.
+        return Signature(signature, instructions)
+    if instructions is not None:
+        raise ValueError(
+            "Don't specify instructions when initializing with a Signature"
+        )
+    return signature