Use shared `is_async_callable` instead of `inspect.iscoroutinefunction` by Kludex · Pull Request #2389 · modelcontextprotocol/python-sdk · GitHub
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Use shared is_async_callable instead of inspect.iscoroutinefunction #2389

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Merged
maxisbey merged 3 commits into from
Apr 8, 2026
Merged

Use shared is_async_callable instead of inspect.iscoroutinefunction #2389

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1995794
Use shared `is_async_callable` instead of `inspect.iscoroutinefunction`
Kludex Apr 3, 2026
a8340e4
Add reference link to Starlette source in docstring
Kludex Apr 3, 2026
cfafb2f
Use correct branch name in Starlette reference link
Kludex Apr 3, 2026
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7 changes: 4 additions & 3 deletions src/mcp/server/mcpserver/prompts/base.py
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7 changes: 4 additions & 3 deletions src/mcp/server/mcpserver/resources/templates.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
from __future__ import annotations

import functools
import inspect
import re
from collections.abc import Callable
from typing import TYPE_CHECKING, Any
Expand All @@ -15,6 +14,7 @@
from mcp.server.mcpserver.resources.types import FunctionResource, Resource
from mcp.server.mcpserver.utilities.context_injection import find_context_parameter, inject_context
from mcp.server.mcpserver.utilities.func_metadata import func_metadata
from mcp.shared._callable_inspection import is_async_callable
from mcp.types import Annotations, Icon

if TYPE_CHECKING:
Expand Down Expand Up @@ -112,8 +112,9 @@ async def create_resource(
# Add context to params if needed
params = inject_context(self.fn, params, context, self.context_kwarg)

if inspect.iscoroutinefunction(self.fn):
result = await self.fn(**params)
fn = self.fn
if is_async_callable(fn):
result = await fn(**params)
else:
result = await anyio.to_thread.run_sync(functools.partial(self.fn, **params))

Expand Down
11 changes: 7 additions & 4 deletions src/mcp/server/mcpserver/resources/types.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
"""Concrete resource implementations."""

import inspect
from __future__ import annotations

import json
from collections.abc import Callable
from pathlib import Path
Expand All @@ -14,6 +15,7 @@
from pydantic import Field, ValidationInfo, validate_call

from mcp.server.mcpserver.resources.base import Resource
from mcp.shared._callable_inspection import is_async_callable
from mcp.types import Annotations, Icon


Expand Down Expand Up @@ -55,8 +57,9 @@ class FunctionResource(Resource):
async def read(self) -> str | bytes:
"""Read the resource by calling the wrapped function."""
try:
if inspect.iscoroutinefunction(self.fn):
result = await self.fn()
fn = self.fn
if is_async_callable(fn):
result = await fn()
else:
result = await anyio.to_thread.run_sync(self.fn)

Expand All @@ -83,7 +86,7 @@ def from_function(
icons: list[Icon] | None = None,
annotations: Annotations | None = None,
meta: dict[str, Any] | None = None,
) -> "FunctionResource":
) -> FunctionResource:
"""Create a FunctionResource from a function."""
func_name = name or fn.__name__
if func_name == "<lambda>": # pragma: no cover
Expand Down
14 changes: 2 additions & 12 deletions src/mcp/server/mcpserver/tools/base.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
from __future__ import annotations

import functools
import inspect
from collections.abc import Callable
from functools import cached_property
from typing import TYPE_CHECKING, Any
Expand All @@ -11,6 +9,7 @@
from mcp.server.mcpserver.exceptions import ToolError
from mcp.server.mcpserver.utilities.context_injection import find_context_parameter
from mcp.server.mcpserver.utilities.func_metadata import FuncMetadata, func_metadata
from mcp.shared._callable_inspection import is_async_callable
from mcp.shared.exceptions import UrlElicitationRequiredError
from mcp.shared.tool_name_validation import validate_and_warn_tool_name
from mcp.types import Icon, ToolAnnotations
Expand Down Expand Up @@ -63,7 +62,7 @@ def from_function(
raise ValueError("You must provide a name for lambda functions")

func_doc = description or fn.__doc__ or ""
is_async = _is_async_callable(fn)
is_async = is_async_callable(fn)

if context_kwarg is None: # pragma: no branch
context_kwarg = find_context_parameter(fn)
Expand Down Expand Up @@ -118,12 +117,3 @@ async def run(
raise
except Exception as e:
raise ToolError(f"Error executing tool {self.name}: {e}") from e


def _is_async_callable(obj: Any) -> bool:
while isinstance(obj, functools.partial): # pragma: lax no cover
obj = obj.func

return inspect.iscoroutinefunction(obj) or (
callable(obj) and inspect.iscoroutinefunction(getattr(obj, "__call__", None))
)
33 changes: 33 additions & 0 deletions src/mcp/shared/_callable_inspection.py
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