Support late-configuration of LM to fix certain tests.

Author: FireMasterK

dspy/predict/chain_of_thought.py

@@ -3,6 +3,7 @@
 from pydantic.fields import FieldInfo
 
 import dspy
+from dspy.clients.base_lm import BaseLM
 from dspy.primitives.module import Module
 from dspy.signatures.field import OutputField
 from dspy.signatures.signature import Signature, ensure_signature
@@ -27,18 +28,42 @@ def __init__(
         """
         super().__init__()
         signature = ensure_signature(signature)
-        if dspy.settings.lm.reasoning_model:
-            self.predict = dspy.Predict(signature, **config)
-        else:
-            prefix = "Reasoning: Let's think step by step in order to"
-            desc = "${reasoning}"
-            rationale_field_type = rationale_field.annotation if rationale_field else rationale_field_type
-            rationale_field = rationale_field if rationale_field else dspy.OutputField(prefix=prefix, desc=desc)
-            extended_signature = signature.prepend(name="reasoning", field=rationale_field, type_=rationale_field_type)
-            self.predict = dspy.Predict(extended_signature, **config)
+        self.predict_reasoning = dspy.Predict(signature, **config)
+        prefix = "Reasoning: Let's think step by step in order to"
+        desc = "${reasoning}"
+        rationale_field_type = rationale_field.annotation if rationale_field else rationale_field_type
+        rationale_field = rationale_field if rationale_field else dspy.OutputField(prefix=prefix, desc=desc)
+        extended_signature = signature.prepend(name="reasoning", field=rationale_field, type_=rationale_field_type)
+        self.predict = dspy.Predict(extended_signature, **config)
+
+    def _validate_lm(self, **kwargs):
+        """Helper method to validate the LM configuration."""
+        lm = kwargs.get("lm", dspy.settings.lm)
+
+        if lm is None:
+            raise ValueError(
+                "No LM is loaded. Please configure the LM using `dspy.configure(lm=dspy.LM(...))`. e.g, "
+                "`dspy.configure(lm=dspy.LM('openai/gpt-4o-mini'))`"
+            )
+
+        if isinstance(lm, str):
+            # Many users mistakenly use `dspy.configure(lm="openai/gpt-4o-mini")` instead of
+            # `dspy.configure(lm=dspy.LM("openai/gpt-4o-mini"))`, so we are providing a specific error message.
+            raise ValueError(
+                f"LM must be an instance of `dspy.BaseLM`, not a string. Instead of using a string like "
+                f"'dspy.configure(lm=\"{lm}\")', please configure the LM like 'dspy.configure(lm=dspy.LM(\"{lm}\"))'"
+            )
+        elif not isinstance(lm, BaseLM):
+            raise ValueError(f"LM must be an instance of `dspy.BaseLM`, not {type(lm)}. Received `lm={lm}`.")
+
+        return lm
 
     def forward(self, **kwargs):
-        return self.predict(**kwargs)
+        lm = self._validate_lm(**kwargs)
+        return self.predict(**kwargs) if not lm.reasoning_model else self.predict_reasoning(**kwargs)
 
     async def aforward(self, **kwargs):
-        return await self.predict.acall(**kwargs)
+        lm = self._validate_lm(**kwargs)
+        return await (
+            self.predict.acall(**kwargs) if not lm.reasoning_model else self.predict_reasoning.acall(**kwargs)
+        )

tests/predict/test_chain_of_thought.py

@@ -31,7 +31,7 @@ def test_cot_skips_with_reasoning_model():
     dspy.settings.configure(lm=lm)
     signature = dspy.Signature("question -> answer")
     predict = ChainOfThought(signature)
-    assert list(predict.predict.signature.output_fields.keys()) == [
+    assert list(predict.predict_reasoning.signature.output_fields.keys()) == [
         "answer",
     ]
     assert predict(question="What is 1+1?").answer == "2"