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Return objects from decorators

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This commit is contained in:
Jeremiah Lowin 2025-06-05 10:04:39 -04:00
commit d26a5dffc3
3 changed files with 61 additions and 67 deletions
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67
src/fastmcp/server/server.py
View file

@ -14,7 +14,7 @@ from contextlib import (
)
from functools import partial
from pathlib import Path
from typing import TYPE_CHECKING, Any, Generic, Literal
from typing import TYPE_CHECKING, Any, Generic, Literal, overload
import anyio
import httpx
@ -45,6 +45,7 @@ import fastmcp.server
import fastmcp.settings
from fastmcp.exceptions import NotFoundError
from fastmcp.prompts import Prompt, PromptManager
from fastmcp.prompts.prompt import FunctionPrompt
from fastmcp.resources import Resource, ResourceManager
from fastmcp.resources.template import ResourceTemplate
from fastmcp.server.auth.auth import OAuthProvider
@ -55,7 +56,7 @@ from fastmcp.server.http import (
create_streamable_http_app,
)
from fastmcp.tools import ToolManager
from fastmcp.tools.tool import Tool
from fastmcp.tools.tool import FunctionTool, Tool
from fastmcp.utilities.cache import TimedCache
from fastmcp.utilities.logging import get_logger
from fastmcp.utilities.mcp_config import MCPConfig
@ -510,6 +511,30 @@ class FastMCP(Generic[LifespanResultT]):
self._tool_manager.remove_tool(name)
self._cache.clear()
@overload
def tool(
self,
name_or_fn: AnyFunction,
*,
name: str | None = None,
description: str | None = None,
tags: set[str] | None = None,
annotations: ToolAnnotations | dict[str, Any] | None = None,
exclude_args: list[str] | None = None,
) -> FunctionTool: ...
@overload
def tool(
self,
name_or_fn: str | None = None,
*,
name: str | None = None,
description: str | None = None,
tags: set[str] | None = None,
annotations: ToolAnnotations | dict[str, Any] | None = None,
exclude_args: list[str] | None = None,
) -> Callable[[AnyFunction], FunctionTool]: ...
def tool(
self,
name_or_fn: str | AnyFunction | None = None,
@ -519,7 +544,7 @@ class FastMCP(Generic[LifespanResultT]):
tags: set[str] | None = None,
annotations: ToolAnnotations | dict[str, Any] | None = None,
exclude_args: list[str] | None = None,
) -> Callable[[AnyFunction], AnyFunction] | AnyFunction:
) -> Callable[[AnyFunction], FunctionTool] | FunctionTool:
"""Decorator to register a tool.
Tools can optionally request a Context object by adding a parameter with the
@ -571,7 +596,7 @@ class FastMCP(Generic[LifespanResultT]):
fn = name_or_fn
tool_name = name # Use keyword name if provided, otherwise None
# Register the tool immediately and return the function
# Register the tool immediately and return the tool object
tool = Tool.from_function(
fn,
name=tool_name,
@ -582,7 +607,7 @@ class FastMCP(Generic[LifespanResultT]):
serializer=self._tool_serializer,
)
self.add_tool(tool)
return fn
return tool
elif isinstance(name_or_fn, str):
# Case 3: @tool("custom_name") - name passed as first argument
@ -674,7 +699,7 @@ class FastMCP(Generic[LifespanResultT]):
description: str | None = None,
mime_type: str | None = None,
tags: set[str] | None = None,
) -> Callable[[AnyFunction], AnyFunction]:
) -> Callable[[AnyFunction], Resource | ResourceTemplate]:
"""Decorator to register a function as a resource.
The function will be called when the resource is read to generate its content.
@ -728,7 +753,7 @@ class FastMCP(Generic[LifespanResultT]):
"Did you forget to call it? Use @resource('uri') instead of @resource"
)
def decorator(fn: AnyFunction) -> AnyFunction:
def decorator(fn: AnyFunction) -> Resource | ResourceTemplate:
from fastmcp.server.context import Context
# Check if this should be a template
@ -750,6 +775,7 @@ class FastMCP(Generic[LifespanResultT]):
tags=tags,
)
self.add_template(template)
return template
elif not has_uri_params and not has_func_params:
resource = Resource.from_function(
fn=fn,
@ -760,14 +786,13 @@ class FastMCP(Generic[LifespanResultT]):
tags=tags,
)
self.add_resource(resource)
return resource
else:
raise ValueError(
"Invalid resource or template definition due to a "
"mismatch between URI parameters and function parameters."
)
return fn
return decorator
def add_prompt(self, prompt: Prompt) -> None:
@ -779,6 +804,26 @@ class FastMCP(Generic[LifespanResultT]):
self._prompt_manager.add_prompt(prompt)
self._cache.clear()
@overload
def prompt(
self,
name_or_fn: AnyFunction,
*,
name: str | None = None,
description: str | None = None,
tags: set[str] | None = None,
) -> FunctionPrompt: ...
@overload
def prompt(
self,
name_or_fn: str | None = None,
*,
name: str | None = None,
description: str | None = None,
tags: set[str] | None = None,
) -> Callable[[AnyFunction], FunctionPrompt]: ...
def prompt(
self,
name_or_fn: str | AnyFunction | None = None,
@ -786,7 +831,7 @@ class FastMCP(Generic[LifespanResultT]):
name: str | None = None,
description: str | None = None,
tags: set[str] | None = None,
) -> Callable[[AnyFunction], AnyFunction] | AnyFunction:
) -> Callable[[AnyFunction], FunctionPrompt] | FunctionPrompt:
"""Decorator to register a prompt.
Prompts can optionally request a Context object by adding a parameter with the
@ -867,7 +912,7 @@ class FastMCP(Generic[LifespanResultT]):
)
self.add_prompt(prompt)
return fn
return prompt
elif isinstance(name_or_fn, str):
# Case 3: @prompt("custom_name") - name passed as first argument

11
tests/server/test_server.py
View file

@ -6,7 +6,7 @@ from pydantic import Field
from fastmcp import Client, FastMCP
from fastmcp.exceptions import NotFoundError
from fastmcp.prompts.prompt import Prompt
from fastmcp.prompts.prompt import FunctionPrompt, Prompt
from fastmcp.resources import Resource, ResourceTemplate
from fastmcp.server.server import (
MountedServer,
@ -179,7 +179,6 @@ class TestToolDecorator:
def __init__(self, x: int):
self.x = x
@mcp.tool
def add(self, y: int) -> int:
return self.x + y
@ -326,11 +325,11 @@ class TestToolDecorator:
result_fn = mcp.tool(standalone_function, name="direct_call_tool")
# The function should be returned unchanged
assert result_fn is standalone_function
assert isinstance(result_fn, FunctionTool)
# Verify the tool was registered correctly
tools = await mcp.get_tools()
assert "direct_call_tool" in tools
assert tools["direct_call_tool"] is result_fn
# Verify it can be called
result = await mcp._mcp_call_tool("direct_call_tool", {"x": 5, "y": 3})
@ -857,11 +856,11 @@ class TestPromptDecorator:
result_fn = mcp.prompt(standalone_function, name="direct_call_prompt")
# The function should be returned unchanged
assert result_fn is standalone_function
assert isinstance(result_fn, FunctionPrompt)
# Verify the prompt was registered correctly
prompts = await mcp.get_prompts()
assert "direct_call_prompt" in prompts
assert prompts["direct_call_prompt"] is result_fn
# Verify it can be called
async with Client(mcp) as client:

50
tests/server/test_server_interactions.py
View file

@ -936,56 +936,6 @@ class TestResourceTemplates:
result = await client.read_resource(AnyUrl("resource://test/data"))
assert result[0].text == "Data for test" # type: ignore[attr-defined]
async def test_stacked_resource_template_decorators(self):
"""Test that resource template decorators can be stacked."""
mcp = FastMCP()
@mcp.resource("users://email/{email}")
@mcp.resource("users://name/{name}")
def lookup_user(name: str | None = None, email: str | None = None) -> dict:
if name:
return {
"id": "123",
"name": name,
"email": "dummy@example.com",
"lookup": "name",
}
elif email:
return {
"id": "123",
"name": "Test User",
"email": email,
"lookup": "email",
}
else:
raise ValueError("Either name or email must be provided")
# Verify both templates are registered
templates_dict = await mcp.get_resource_templates()
templates = list(templates_dict.values())
assert len(templates) == 2
template_uris = {t.uri_template for t in templates}
assert "users://email/{email}" in template_uris
assert "users://name/{name}" in template_uris
# Test lookup by email
async with Client(mcp) as client:
email_result = await client.read_resource(
AnyUrl("users://email/user@example.com")
)
assert email_result[0].text # type: ignore[attr-defined]
email_data = json.loads(email_result[0].text) # type: ignore[attr-defined]
assert email_data["lookup"] == "email"
assert email_data["email"] == "user@example.com"
# Test lookup by name
name_result = await client.read_resource(AnyUrl("users://name/John"))
assert name_result[0].text # type: ignore[attr-defined]
name_data = json.loads(name_result[0].text) # type: ignore[attr-defined]
assert name_data["lookup"] == "name"
assert name_data["name"] == "John"
assert name_data["email"] == "dummy@example.com"
async def test_template_decorator_with_tags(self):
mcp = FastMCP()