fix: reject Python keywords as field names

CHANGELOG.md

@@ -13,7 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - First‑class support for **open‑source models via third‑party providers** (e.g. OpenRouter, Groq and similar gateways), alongside existing Ollama + cloud integrations.
 
 ### Fixed
-- TBC
+- Reject Python keywords as field names before generating DSPy signatures.
 
 ---
 

dspy_code/validation/input_validator.py

@@ -4,6 +4,7 @@
 Provides validation methods for user input during interactive task collection.
 """
 
+import keyword
 from typing import Any
 
 
@@ -27,7 +28,7 @@ def validate_field_name(self, name: str) -> str:
 
         # Check for valid Python identifier
         name = name.strip()
-        if not name.isidentifier():
+        if not name.isidentifier() or keyword.iskeyword(name):
             raise ValidationError(f"'{name}' is not a valid Python identifier")
 
         return name

tests/test_input_field_names.py

@@ -0,0 +1,20 @@
+"""Field names must be usable in generated Python signatures."""
+
+import keyword
+
+import pytest
+
+from dspy_code.validation.input_validator import InputValidator, ValidationError
+
+
+@pytest.mark.parametrize("name", keyword.kwlist)
+def test_field_name_rejects_python_keywords(name):
+    with pytest.raises(ValidationError, match="not a valid Python identifier"):
+        InputValidator().validate_field_name(name)
+
+
+@pytest.mark.parametrize("name", ["question", "class_", "_answer", "café", "match", "case"])
+def test_field_name_accepts_usable_identifiers(name):
+    validated = InputValidator().validate_field_name("  " + name + "  ")
+    assert validated == name
+    compile(f"class Signature:\n    {validated}: str\n", "<signature>", "exec")