fix(observe): resolve names for partial functions

langfuse/_client/observe.py

@@ -2,7 +2,7 @@
 import contextvars
 import inspect
 import os
-from functools import wraps
+from functools import partial, wraps
 from typing import (
     Any,
     AsyncGenerator,
@@ -60,6 +60,12 @@ def _is_coroutine_function(func: Any) -> bool:
     )
 
 
+def _get_function_name(func: Callable[..., Any]) -> str:
+    while isinstance(func, partial) and not hasattr(func, "__name__"):
+        func = func.func
+    return func.__name__
+
+
 class LangfuseDecorator:
     """Implementation of the @observe decorator for seamless Langfuse tracing integration.
 
@@ -275,7 +281,7 @@ async def async_wrapper(*args: Tuple[Any], **kwargs: Dict[str, Any]) -> Any:
                 if trace_id
                 else None
             )
-            final_name = name or func.__name__
+            final_name = name or _get_function_name(func)
             input = (
                 self._get_input_from_func_args(
                     is_method=self._is_method(func),
@@ -366,7 +372,7 @@ def sync_wrapper(*args: Any, **kwargs: Any) -> Any:
                 if trace_id
                 else None
             )
-            final_name = name or func.__name__
+            final_name = name or _get_function_name(func)
             input = (
                 self._get_input_from_func_args(
                     is_method=self._is_method(func),

tests/unit/test_observe.py

@@ -3,6 +3,7 @@
 import gc
 import inspect
 import json
+from functools import partial
 from typing import Any, AsyncGenerator, Generator, cast
 
 import pytest
@@ -33,6 +34,76 @@ def _finished_spans_by_name(memory_exporter: Any, name: str) -> list[Any]:
     return [span for span in memory_exporter.get_finished_spans() if span.name == name]
 
 
+@pytest.mark.parametrize("name", [None, "custom_name"])
+def test_observe_partial_function(
+    langfuse_memory_client: Any, memory_exporter: Any, name: str | None
+) -> None:
+    def add(first: int, second: int, *, extra: int = 0) -> int:
+        return first + second + extra
+
+    observed = observe(name=name)(partial(add, 2, extra=4))
+
+    assert observed(3) == 9
+
+    langfuse_memory_client.flush()
+
+    spans = memory_exporter.get_finished_spans()
+    assert len(spans) == 1
+    assert spans[0].name == (name or "add")
+    assert (
+        json.loads(spans[0].attributes[LangfuseOtelSpanAttributes.OBSERVATION_OUTPUT])
+        == 9
+    )
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("name", [None, "custom_name"])
+async def test_observe_async_partial_function(
+    langfuse_memory_client: Any, memory_exporter: Any, name: str | None
+) -> None:
+    async def add(first: int, second: int, *, extra: int = 0) -> int:
+        await asyncio.sleep(0)
+        return first + second + extra
+
+    observed = observe(name=name)(partial(add, 2, extra=4))
+
+    assert inspect.iscoroutinefunction(observed)
+    assert await observed(3) == 9
+
+    langfuse_memory_client.flush()
+
+    spans = memory_exporter.get_finished_spans()
+    assert len(spans) == 1
+    assert spans[0].name == (name or "add")
+    assert (
+        json.loads(spans[0].attributes[LangfuseOtelSpanAttributes.OBSERVATION_OUTPUT])
+        == 9
+    )
+
+
+@pytest.mark.parametrize("function_name", [None, "custom_add"])
+def test_observe_nested_partial_function(
+    langfuse_memory_client: Any, memory_exporter: Any, function_name: str | None
+) -> None:
+    def add(first: int, second: int) -> int:
+        return first + second
+
+    inner = partial(add, 2)
+    # Partials with attributes are not flattened when wrapped in another partial.
+    cast(Any, inner).description = "bound first argument"
+    if function_name:
+        cast(Any, inner).__name__ = function_name
+    observed = observe(partial(inner, 3))
+
+    assert observed() == 5
+
+    langfuse_memory_client.flush()
+
+    spans = memory_exporter.get_finished_spans()
+    assert len(spans) == 1
+    assert spans[0].name == (function_name or "add")
+
+
 @pytest.mark.asyncio
 async def test_capture_output_false_preserves_type_when_current_span_is_updated(
     langfuse_memory_client: Any, memory_exporter: Any