fix: detect uvloop and skip nest_asyncio to prevent patching errors (#2369)

## Issue Link / Problem Description
<!-- Link to related issue or describe the problem this PR solves -->
- Fixes #2357

Author: anistark

src/ragas/async_utils.py

@@ -19,18 +19,40 @@ def is_event_loop_running() -> bool:
         return loop.is_running()
 
 
-def apply_nest_asyncio():
-    """Apply nest_asyncio if an event loop is running."""
-    if is_event_loop_running():
-        # an event loop is running so call nested_asyncio to fix this
-        try:
-            import nest_asyncio
-        except ImportError:
-            raise ImportError(
-                "It seems like your running this in a jupyter-like environment. Please install nest_asyncio with `pip install nest_asyncio` to make it work."
+def apply_nest_asyncio() -> bool:
+    """
+    Apply nest_asyncio if an event loop is running and compatible.
+
+    Returns:
+        bool: True if nest_asyncio was applied, False if skipped
+    """
+    if not is_event_loop_running():
+        return False
+
+    try:
+        import nest_asyncio
+    except ImportError:
+        raise ImportError(
+            "It seems like your running this in a jupyter-like environment. Please install nest_asyncio with `pip install nest_asyncio` to make it work."
+        )
+
+    try:
+        loop = asyncio.get_running_loop()
+        loop_type = type(loop).__name__
+
+        if "uvloop" in loop_type.lower() or "uvloop" in str(type(loop)):
+            logger.debug(
+                f"Skipping nest_asyncio.apply() for incompatible loop type: {loop_type}"
             )
+            return False
 
         nest_asyncio.apply()
+        return True
+    except ValueError as e:
+        if "Can't patch loop of type" in str(e):
+            logger.debug(f"Skipping nest_asyncio.apply(): {e}")
+            return False
+        raise
 
 
 def as_completed(
@@ -116,12 +138,22 @@ def run(
         Whether to apply nest_asyncio for Jupyter compatibility. Default is True.
         Set to False in production environments to avoid event loop patching.
     """
-    # Only apply nest_asyncio if explicitly allowed
+    nest_asyncio_applied = False
     if allow_nest_asyncio:
-        apply_nest_asyncio()
+        nest_asyncio_applied = apply_nest_asyncio()
 
-    # Create the coroutine if it's a callable, otherwise use directly
     coro = async_func() if callable(async_func) else async_func
+
+    if is_event_loop_running() and not nest_asyncio_applied:
+        loop = asyncio.get_running_loop()
+        loop_type = type(loop).__name__
+        raise RuntimeError(
+            f"Cannot execute nested async code with {loop_type}. "
+            f"uvloop does not support nested event loop execution. "
+            f"Please use asyncio's standard event loop in Jupyter environments, "
+            f"or refactor your code to avoid nested async calls."
+        )
+
     return asyncio.run(coro)
 
 

tests/unit/test_uvloop_compatibility.py

@@ -0,0 +1,92 @@
+"""Test uvloop compatibility with nest_asyncio."""
+
+import asyncio
+import sys
+
+import pytest
+
+
+class TestUvloopCompatibility:
+    """Test that ragas works with uvloop event loops."""
+
+    @pytest.mark.skipif(sys.version_info < (3, 8), reason="uvloop requires Python 3.8+")
+    def test_apply_nest_asyncio_with_uvloop_returns_false(self):
+        """Test that apply_nest_asyncio returns False with uvloop."""
+        uvloop = pytest.importorskip("uvloop")
+
+        from ragas.async_utils import apply_nest_asyncio
+
+        async def test_func():
+            result = apply_nest_asyncio()
+            return result
+
+        uvloop.install()
+        try:
+            result = asyncio.run(test_func())
+            assert result is False
+        finally:
+            asyncio.set_event_loop_policy(None)
+
+    @pytest.mark.skipif(sys.version_info < (3, 8), reason="uvloop requires Python 3.8+")
+    def test_run_with_uvloop_and_running_loop(self):
+        """Test that run() raises clear error with uvloop in running event loop (Jupyter scenario)."""
+        uvloop = pytest.importorskip("uvloop")
+
+        from ragas.async_utils import run
+
+        async def inner_task():
+            return "success"
+
+        async def outer_task():
+            with pytest.raises(RuntimeError, match="Cannot execute nested async code"):
+                run(inner_task)
+
+        uvloop.install()
+        try:
+            asyncio.run(outer_task())
+        finally:
+            asyncio.set_event_loop_policy(None)
+
+    @pytest.mark.skipif(sys.version_info < (3, 8), reason="uvloop requires Python 3.8+")
+    def test_run_async_tasks_with_uvloop(self):
+        """Test that run_async_tasks works with uvloop."""
+        uvloop = pytest.importorskip("uvloop")
+
+        from ragas.async_utils import run_async_tasks
+
+        async def task(n):
+            return n * 2
+
+        tasks = [task(i) for i in range(5)]
+
+        uvloop.install()
+        try:
+            results = run_async_tasks(tasks, show_progress=False)
+            assert sorted(results) == [0, 2, 4, 6, 8]
+        finally:
+            asyncio.set_event_loop_policy(None)
+
+    def test_apply_nest_asyncio_without_uvloop_returns_true(self):
+        """Test that apply_nest_asyncio returns True with standard asyncio."""
+        from ragas.async_utils import apply_nest_asyncio
+
+        async def test_func():
+            result = apply_nest_asyncio()
+            return result
+
+        result = asyncio.run(test_func())
+        assert result is True
+
+    def test_run_with_standard_asyncio_and_running_loop(self):
+        """Test that run() works with standard asyncio in a running loop."""
+        from ragas.async_utils import run
+
+        async def inner_task():
+            return "nested_success"
+
+        async def outer_task():
+            result = run(inner_task)
+            return result
+
+        result = asyncio.run(outer_task())
+        assert result == "nested_success"