also implement singleton patton with lazy loading similar to Settings class

Author: SimonBlanke

openml/_api/__init__.py

@@ -2,7 +2,4 @@
 
 
 def set_api_version(version: str, *, strict: bool = False) -> None:
-    api_context.set_version(version=version, strict=strict)
-
-
-api_context = APIContext()
+    APIContext.get().set_version(version=version, strict=strict)

openml/_api/runtime/core.py

@@ -94,9 +94,29 @@ def build_backend(version: str, *, strict: bool) -> APIBackend:
 
 
 class APIContext:
+    """Context for API version management.
+
+    Uses singleton pattern to avoid circular imports. The instance is created
+    lazily on first access via get(), not at module load time.
+    """
+
+    _instance: APIContext | None = None
+
     def __init__(self) -> None:
         self._backend = build_backend("v1", strict=False)
 
+    @classmethod
+    def get(cls) -> APIContext:
+        """Get the singleton instance, creating it on first access."""
+        if cls._instance is None:
+            cls._instance = cls()
+        return cls._instance
+
+    @classmethod
+    def reset(cls) -> None:
+        """Reset the singleton instance. Useful for testing."""
+        cls._instance = None
+
     def set_version(self, version: str, *, strict: bool = False) -> None:
         self._backend = build_backend(version=version, strict=strict)