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Merge pull request #727 from jlowin/decorators

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Return objects from FastMCP decorators
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Jeremiah Lowin 2025-06-05 11:22:13 -04:00 • committed by GitHub
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118
docs/patterns/decorating-methods.mdx
View file

@ -16,11 +16,36 @@ When you apply a FastMCP decorator like `@tool`, `@resource()`, or `@prompt()` t
This means directly decorating these methods doesn't work as expected. In practice, the LLM would see parameters like `self` or `cls` that it cannot provide values for.
Additionally, **FastMCP decorators return objects (Tool, Resource, or Prompt instances) rather than the original function**. This means that when you decorate a method directly, the method becomes the returned object and is no longer callable by your code:
<Warning>
**Don't do this!**
The method will no longer be callable from Python, and the tool won't be callable by LLMs.
```python
from fastmcp import FastMCP
mcp = FastMCP()
class MyClass:
@mcp.tool()
def my_method(self, x: int) -> int:
return x * 2
obj = MyClass()
obj.my_method(5) # Fails - my_method is a Tool, not a function
```
</Warning>
This is another important reason to register methods functionally after defining the class.
## Recommended Patterns
### Instance Methods
**Don't do this** (it doesn't work properly):
<Warning>
**Don't do this!**
```python
from fastmcp import FastMCP
@ -28,17 +53,14 @@ from fastmcp import FastMCP
mcp = FastMCP()
class MyClass:
@mcp.tool() # This won't work correctly
@mcp.tool() # This won't work correctly
def add(self, x, y):
return x + y
@mcp.resource("resource://{param}") # This won't work correctly
def get_resource(self, param: str):
return f"Resource data for {param}"
```
</Warning>
When the decorator is applied this way, it captures the unbound method. When the LLM later tries to use this component, it will see `self` as a required parameter, but it won't know what to provide for it, causing errors or unexpected behavior.
<Check>
**Do this instead**:
```python
@ -49,21 +71,15 @@ mcp = FastMCP()
class MyClass:
def add(self, x, y):
return x + y
def get_resource(self, param: str):
return f"Resource data for {param}"
# Create an instance first, then add the bound methods
# Create an instance first, then register the bound methods
obj = MyClass()
mcp.add_tool(obj.add)
mcp.add_resource_fn(obj.get_resource, uri="resource://{param}") # For resources or templates
# Note: FastMCP provides add_resource() for adding Resource objects directly and
# add_resource_fn() for adding functions that generate resources or templates
mcp.tool(obj.add)
# Now you can call it without 'self' showing up as a parameter
await mcp.call_tool('add', {'x': 1, 'y': 2}) # Returns 3
await mcp._mcp_call_tool('add', {'x': 1, 'y': 2}) # Returns 3
```
</Check>
This approach works because:
1. You first create an instance of the class (`obj`)
@ -72,9 +88,10 @@ This approach works because:
### Class Methods
Similar to instance methods, decorating class methods directly doesn't work properly:
The behavior of decorating class methods depends on the order of decorators:
**Don't do this**:
<Warning>
**Don't do this** (decorator order matters):
```python
from fastmcp import FastMCP
@ -83,13 +100,21 @@ mcp = FastMCP()
class MyClass:
@classmethod
@mcp.tool() # This won't work correctly
def from_string(cls, s):
@mcp.tool() # This won't work but won't raise an error
def from_string_v1(cls, s):
return cls(s)
@mcp.tool()
@classmethod # This will raise a helpful ValueError
def from_string_v2(cls, s):
return cls(s)
```
</Warning>
The problem here is that the FastMCP decorator is applied before the `@classmethod` decorator (Python applies decorators bottom-to-top). So it captures the function before it's transformed into a class method, leading to incorrect behavior.
- If `@classmethod` comes first, then `@mcp.tool()`: No error is raised, but it won't work correctly
- If `@mcp.tool()` comes first, then `@classmethod`: FastMCP will detect this and raise a helpful `ValueError` with guidance
<Check>
**Do this instead**:
```python
@ -102,9 +127,10 @@ class MyClass:
def from_string(cls, s):
return cls(s)
# Add the class method after the class is defined
mcp.add_tool(MyClass.from_string)
# Register the class method after the class is defined
mcp.tool(MyClass.from_string)
```
</Check>
This works because:
1. The `@classmethod` decorator is applied properly during class definition
@ -113,7 +139,10 @@ This works because:
### Static Methods
Unlike instance and class methods, static methods work fine with FastMCP decorators:
Static methods "work" with FastMCP decorators, but this is not recommended because the FastMCP decorator will not return a callable method. Therefore, you should register static methods the same way as other methods.
<Warning>
**This is not recommended, though it will work.**
```python
from fastmcp import FastMCP
@ -121,23 +150,17 @@ from fastmcp import FastMCP
mcp = FastMCP()
class MyClass:
@mcp.tool()
@staticmethod
@mcp.tool() # This works!
def utility(x, y):
return x + y
@staticmethod
@mcp.resource("resource://data") # This works too!
def get_data():
return "Static resource data"
```
</Warning>
This approach works because:
1. The `@staticmethod` decorator is applied first (executed last), transforming the method into a regular function
2. When the FastMCP decorator is applied, it's capturing what is effectively just a regular function
3. A static method doesn't have any binding requirements - it doesn't receive a `self` or `cls` parameter
This works because `@staticmethod` converts the method to a regular function, which the FastMCP decorator can then properly process. However, this is not recommended because the FastMCP decorator will not return a callable staticmethod. Therefore, you should register static methods the same way as other methods.
Alternatively, you can use the same pattern as the other methods:
<Check>
**Prefer this pattern:**
```python
from fastmcp import FastMCP
@ -150,10 +173,9 @@ class MyClass:
return x + y
# This also works
mcp.add_tool(MyClass.utility)
mcp.tool(MyClass.utility)
```
This works for the same reason - a static method is essentially just a function in a class namespace.
</Check>
## Additional Patterns
@ -169,8 +191,8 @@ mcp = FastMCP()
class ComponentProvider:
def __init__(self, mcp_instance):
# Register methods
mcp_instance.add_tool(self.tool_method)
mcp_instance.add_resource_fn(self.resource_method, uri="resource://data")
mcp_instance.tool(self.tool_method)
mcp_instance.resource("resource://data")(self.resource_method)
def tool_method(self, x):
return x * 2
@ -191,11 +213,13 @@ The class automatically registers its methods during initialization, ensuring th
## Summary
While FastMCP's decorator pattern works seamlessly with regular functions and static methods, for instance methods and class methods, you should add them after creating the instance or class. This ensures that the methods are properly bound before being registered.
The current behavior of FastMCP decorators with methods is:
These patterns apply to all FastMCP decorators and registration methods:
- `@tool()` and `add_tool`
- `@resource()` and `add_resource_fn()`
- `@prompt()` and `add_prompt()`
- **Static methods**: Can be decorated directly and work perfectly with all FastMCP decorators
- **Class methods**: Cannot be decorated directly and will raise a helpful `ValueError` with guidance
- **Instance methods**: Should be registered after creating an instance using the decorator calls
Understanding these patterns allows you to effectively organize your components into classes while maintaining proper method binding, giving you the benefits of object-oriented design without sacrificing the simplicity of FastMCP's decorator system.
For class and instance methods, you should register them after creating the instance or class to ensure proper method binding. This ensures that the methods are properly bound before being registered.
Understanding these patterns allows you to effectively organize your components into classes while maintaining proper method binding, giving you the benefits of object-oriented design without sacrificing the simplicity of FastMCP's decorator system.

3
src/fastmcp/prompts/prompt.py
View file

@ -171,6 +171,9 @@ class FunctionPrompt(Prompt):
# if the fn is a callable class, we need to get the __call__ method from here out
if not inspect.isroutine(fn):
fn = fn.__call__
# if the fn is a staticmethod, we need to work with the underlying function
if isinstance(fn, staticmethod):
fn = fn.__func__
type_adapter = get_cached_typeadapter(fn)
parameters = type_adapter.json_schema()

4
src/fastmcp/resources/template.py
View file

@ -225,8 +225,12 @@ class FunctionResourceTemplate(ResourceTemplate):
description = description or fn.__doc__
# if the fn is a callable class, we need to get the __call__ method from here out
if not inspect.isroutine(fn):
fn = fn.__call__
# if the fn is a staticmethod, we need to work with the underlying function
if isinstance(fn, staticmethod):
fn = fn.__func__
type_adapter = get_cached_typeadapter(fn)
parameters = type_adapter.json_schema()

116
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
@ -55,9 +56,8 @@ 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.decorators import DecoratedFunction
from fastmcp.utilities.logging import get_logger
from fastmcp.utilities.mcp_config import MCPConfig
@ -511,6 +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,
@ -520,7 +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
@ -565,14 +589,26 @@ class FastMCP(Generic[LifespanResultT]):
if isinstance(annotations, dict):
annotations = ToolAnnotations(**annotations)
if isinstance(name_or_fn, classmethod):
raise ValueError(
inspect.cleandoc(
"""
To decorate a classmethod, first define the method and then call
tool() directly on the method instead of using it as a
decorator. See https://gofastmcp.com/patterns/decorating-methods
for examples and more information.
"""
)
)
# Determine the actual name and function based on the calling pattern
if callable(name_or_fn):
if inspect.isroutine(name_or_fn):
# Case 1: @tool (without parens) - function passed directly
# Case 2: direct call like tool(fn, name="something")
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,
@ -583,7 +619,7 @@ 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
@ -675,7 +711,7 @@ 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.
@ -723,15 +759,27 @@ class FastMCP(Generic[LifespanResultT]):
return f"Weather for {city}: {data}"
"""
# Check if user passed function directly instead of calling decorator
if callable(uri):
if inspect.isroutine(uri):
raise TypeError(
"The @resource decorator was used incorrectly. "
"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
if isinstance(fn, classmethod): # type: ignore[reportUnnecessaryIsInstance]
raise ValueError(
inspect.cleandoc(
"""
To decorate a classmethod, first define the method and then call
resource() directly on the method instead of using it as a
decorator. See https://gofastmcp.com/patterns/decorating-methods
for examples and more information.
"""
)
)
# Check if this should be a template
has_uri_params = "{" in uri and "}" in uri
# check if the function has any parameters (other than injected context)
@ -751,6 +799,7 @@ 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,
@ -761,14 +810,13 @@ 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:
@ -780,6 +828,26 @@ 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,
@ -787,7 +855,7 @@ 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
@ -852,8 +920,21 @@ class FastMCP(Generic[LifespanResultT]):
# Direct function call
server.prompt(my_function, name="custom_name")
"""
if isinstance(name_or_fn, classmethod):
raise ValueError(
inspect.cleandoc(
"""
To decorate a classmethod, first define the method and then call
prompt() directly on the method instead of using it as a
decorator. See https://gofastmcp.com/patterns/decorating-methods
for examples and more information.
"""
)
)
# Determine the actual name and function based on the calling pattern
if callable(name_or_fn):
if inspect.isroutine(name_or_fn):
# Case 1: @prompt (without parens) - function passed directly as decorator
# Case 2: direct call like prompt(fn, name="something")
fn = name_or_fn
@ -868,12 +949,7 @@ class FastMCP(Generic[LifespanResultT]):
)
self.add_prompt(prompt)
# If name is provided, this is a direct call, return original function for consistency with tools
# If name is None, this is @prompt without parens, return DecoratedFunction for proper method handling
if name is not None:
return fn # Direct function call
else:
return DecoratedFunction(fn) # Decorator usage
return prompt
elif isinstance(name_or_fn, str):
# Case 3: @prompt("custom_name") - name passed as first argument

3
src/fastmcp/tools/tool.py
View file

@ -146,6 +146,9 @@ class FunctionTool(Tool):
# if the fn is a callable class, we need to get the __call__ method from here out
if not inspect.isroutine(fn):
fn = fn.__call__
# if the fn is a staticmethod, we need to work with the underlying function
if isinstance(fn, staticmethod):
fn = fn.__func__
type_adapter = get_cached_typeadapter(fn)
schema = type_adapter.json_schema()

101
src/fastmcp/utilities/decorators.py
View file

@ -1,101 +0,0 @@
import inspect
from collections.abc import Callable
from typing import Generic, ParamSpec, TypeVar, cast, overload
from typing_extensions import Self
R = TypeVar("R")
P = ParamSpec("P")
class DecoratedFunction(Generic[P, R]):
"""Descriptor for decorated functions.
You can return this object from a decorator to ensure that it works across
all types of functions: vanilla, instance methods, class methods, and static
methods; both synchronous and asynchronous.
This class is used to store the original function and metadata about how to
register it as a tool.
Example usage:
```python
def my_decorator(fn: Callable[P, R]) -> DecoratedFunction[P, R]:
return DecoratedFunction(fn)
```
On a function:
```python
@my_decorator
def my_function(a: int, b: int) -> int:
return a + b
```
On an instance method:
```python
class Test:
@my_decorator
def my_function(self, a: int, b: int) -> int:
return a + b
```
On a class method:
```python
class Test:
@classmethod
@my_decorator
def my_function(cls, a: int, b: int) -> int:
return a + b
```
Note that for classmethods, the decorator must be applied first, then
`@classmethod` on top.
On a static method:
```python
class Test:
@staticmethod
@my_decorator
def my_function(a: int, b: int) -> int:
return a + b
```
"""
def __init__(self, fn: Callable[P, R]):
self.fn = fn
def __call__(self, *args: P.args, **kwargs: P.kwargs) -> R:
"""Call the original function."""
try:
return self.fn(*args, **kwargs)
except TypeError as e:
if "'classmethod' object is not callable" in str(e):
raise TypeError(
"To apply this decorator to a classmethod, apply the decorator first, then @classmethod on top."
)
raise
@overload
def __get__(self, instance: None, owner: type | None = None) -> Self: ...
@overload
def __get__(
self, instance: object, owner: type | None = None
) -> Callable[P, R]: ...
def __get__(
self, instance: object | None, owner: type | None = None
) -> Self | Callable[P, R]:
"""Return the original function when accessed from an instance, or self when accessed from the class."""
if instance is None:
return self
# Return the original function bound to the instance
return cast(Callable[P, R], self.fn.__get__(instance, owner))
def __repr__(self) -> str:
"""Return a representation that matches Python's function representation."""
module = getattr(self.fn, "__module__", "unknown")
qualname = getattr(self.fn, "__qualname__", str(self.fn))
sig_str = str(inspect.signature(self.fn))
return f"<function {module}.{qualname}{sig_str}>"

96
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
@ -206,8 +205,8 @@ class TestToolDecorator:
mcp = FastMCP()
class MyClass:
@staticmethod
@mcp.tool
@staticmethod
def add(x: int, y: int) -> int:
return x + y
@ -224,6 +223,17 @@ class TestToolDecorator:
result = await mcp._mcp_call_tool("add", {"x": 1, "y": 2})
assert result[0].text == "3" # type: ignore[attr-defined]
async def test_tool_decorator_classmethod_error(self):
mcp = FastMCP()
with pytest.raises(ValueError, match="To decorate a classmethod"):
class MyClass:
@mcp.tool
@classmethod
def add(cls, y: int) -> None:
pass
async def test_tool_decorator_classmethod_async_function(self):
mcp = FastMCP()
@ -250,6 +260,20 @@ class TestToolDecorator:
result = await mcp._mcp_call_tool("add", {"x": 1, "y": 2})
assert result[0].text == "3" # type: ignore[attr-defined]
async def test_tool_decorator_staticmethod_order(self):
"""Test that the recommended decorator order works for static methods"""
mcp = FastMCP()
class MyClass:
@mcp.tool
@staticmethod
def add_v1(x: int, y: int) -> int:
return x + y
# Test that the recommended order works
result = await mcp._mcp_call_tool("add_v1", {"x": 1, "y": 2})
assert result[0].text == "3" # type: ignore[attr-defined]
async def test_tool_decorator_with_tags(self):
"""Test that the tool decorator properly sets tags."""
mcp = FastMCP()
@ -326,11 +350,11 @@ 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})
@ -481,12 +505,23 @@ class TestResourceDecorator:
result = await client.read_resource("resource://data")
assert result[0].text == "Class prefix: Hello, world!" # type: ignore[attr-defined]
async def test_resource_decorator_classmethod_error(self):
mcp = FastMCP()
with pytest.raises(ValueError, match="To decorate a classmethod"):
class MyClass:
@mcp.resource("resource://data")
@classmethod
def get_data(cls) -> None:
pass
async def test_resource_decorator_staticmethod(self):
mcp = FastMCP()
class MyClass:
@staticmethod
@mcp.resource("resource://data")
@staticmethod
def get_data() -> str:
return "Static Hello, world!"
@ -505,6 +540,20 @@ class TestResourceDecorator:
result = await client.read_resource("resource://data")
assert result[0].text == "Async Hello, world!" # type: ignore[attr-defined]
async def test_resource_decorator_staticmethod_order(self):
"""Test that both decorator orders work for static methods"""
mcp = FastMCP()
class MyClass:
@mcp.resource("resource://data") # type: ignore[misc] # Type checker warns but runtime works
@staticmethod
def get_data() -> str:
return "Static Hello, world!"
async with Client(mcp) as client:
result = await client.read_resource("resource://data")
assert result[0].text == "Static Hello, world!" # type: ignore[attr-defined]
class TestTemplateDecorator:
async def test_template_decorator(self):
@ -610,8 +659,8 @@ class TestTemplateDecorator:
mcp = FastMCP()
class MyClass:
@staticmethod
@mcp.resource("resource://{name}/data")
@staticmethod
def get_data(name: str) -> str:
return f"Static Data for {name}"
@ -784,12 +833,23 @@ class TestPromptDecorator:
message = result.messages[0]
assert message.content.text == "Class prefix: Hello, world!" # type: ignore[attr-defined]
async def test_prompt_decorator_classmethod_error(self):
mcp = FastMCP()
with pytest.raises(ValueError, match="To decorate a classmethod"):
class MyClass:
@mcp.prompt
@classmethod
def test_prompt(cls) -> None:
pass
async def test_prompt_decorator_staticmethod(self):
mcp = FastMCP()
class MyClass:
@staticmethod
@mcp.prompt
@staticmethod
def test_prompt() -> str:
return "Static Hello, world!"
@ -857,11 +917,11 @@ 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:
@ -882,6 +942,22 @@ class TestPromptDecorator:
def my_function() -> str:
return "Hello, world!"
async def test_prompt_decorator_staticmethod_order(self):
"""Test that both decorator orders work for static methods"""
mcp = FastMCP()
class MyClass:
@mcp.prompt # type: ignore[misc] # Type checker warns but runtime works
@staticmethod
def test_prompt() -> str:
return "Static Hello, world!"
async with Client(mcp) as client:
result = await client.get_prompt("test_prompt")
assert len(result.messages) == 1
message = result.messages[0]
assert message.content.text == "Static Hello, world!" # type: ignore[attr-defined]
class TestResourcePrefixHelpers:
@pytest.mark.parametrize(

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()

222
tests/utilities/test_decorated_function.py
View file

@ -1,222 +0,0 @@
import functools
from collections.abc import Callable
from typing import Any
import pytest
from fastmcp.utilities.decorators import DecoratedFunction
DECORATOR_CALLED = []
def decorator(fn: Callable[..., Any]) -> DecoratedFunction[..., Any]:
@functools.wraps(fn)
def wrapper(*args: Any, **kwargs: Any) -> Any:
DECORATOR_CALLED.append((args, kwargs))
return fn(*args, **kwargs)
return DecoratedFunction(wrapper)
@pytest.fixture(autouse=True)
def reset_decorator_called():
DECORATOR_CALLED.clear()
yield
DECORATOR_CALLED.clear()
@decorator
def add(a: int, b: int) -> int:
return a + b
@decorator
async def add_async(a: int, b: int) -> int:
return a + b
class DecoratedClass:
def __init__(self, x: int):
self.x = x
@decorator
def add(self, a: int, b: int) -> int:
return a + b + self.x
@decorator
async def add_async(self, a: int, b: int) -> int:
return a + b + self.x
@classmethod
@decorator
def add_classmethod(cls, a: int, b: int) -> int:
return a + b
@staticmethod
@decorator
def add_staticmethod(a: int, b: int) -> int:
return a + b
@classmethod
@decorator
async def add_classmethod_async(cls, a: int, b: int) -> int:
return a + b
@staticmethod
@decorator
async def add_staticmethod_async(a: int, b: int) -> int:
return a + b
@decorator
@classmethod
def add_classmethod_reverse_decorator_order(cls, a: int, b: int) -> int:
return a + b
@decorator
@staticmethod
def add_staticmethod_reverse_decorator_order(a: int, b: int) -> int:
return a + b
@decorator
@classmethod
async def add_classmethod_async_reverse_decorator_order(cls, a: int, b: int) -> int:
return a + b
@decorator
@staticmethod
async def add_staticmethod_async_reverse_decorator_order(a: int, b: int) -> int:
return a + b
def test_add():
assert add(1, 2) == 3
assert DECORATOR_CALLED == [((1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert add(a=3, b=4) == 7
assert DECORATOR_CALLED == [((), {"a": 3, "b": 4})]
async def test_add_async():
assert await add_async(1, 2) == 3
assert DECORATOR_CALLED == [((1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert await add_async(a=3, b=4) == 7
assert DECORATOR_CALLED == [((), {"a": 3, "b": 4})]
def test_instance_method():
obj = DecoratedClass(10)
assert obj.add(2, 3) == 15
assert DECORATOR_CALLED == [((obj, 2, 3), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert obj.add(a=4, b=5) == 19
assert DECORATOR_CALLED == [((obj,), {"a": 4, "b": 5})]
async def test_instance_method_async():
obj = DecoratedClass(10)
assert await obj.add_async(2, 3) == 15
assert DECORATOR_CALLED == [((obj, 2, 3), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert await obj.add_async(a=4, b=5) == 19
assert DECORATOR_CALLED == [((obj,), {"a": 4, "b": 5})]
def test_classmethod():
assert DecoratedClass.add_classmethod(1, 2) == 3
assert DECORATOR_CALLED == [((DecoratedClass, 1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert DecoratedClass.add_classmethod(a=3, b=4) == 7
assert DECORATOR_CALLED == [((DecoratedClass,), {"a": 3, "b": 4})]
DECORATOR_CALLED.clear()
# Test via instance
obj = DecoratedClass(10)
assert obj.add_classmethod(5, 6) == 11
assert DECORATOR_CALLED == [((DecoratedClass, 5, 6), {})]
async def test_classmethod_async():
assert await DecoratedClass.add_classmethod_async(1, 2) == 3
assert DECORATOR_CALLED == [((DecoratedClass, 1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert await DecoratedClass.add_classmethod_async(a=3, b=4) == 7
assert DECORATOR_CALLED == [((DecoratedClass,), {"a": 3, "b": 4})]
DECORATOR_CALLED.clear()
# Test via instance
obj = DecoratedClass(10)
assert await obj.add_classmethod_async(5, 6) == 11
assert DECORATOR_CALLED == [((DecoratedClass, 5, 6), {})]
def test_classmethod_wrong_order():
with pytest.raises(
TypeError,
match="To apply this decorator to a classmethod, apply the decorator first, then @classmethod on top.",
):
DecoratedClass.add_classmethod_reverse_decorator_order(1, 2)
async def test_classmethod_async_wrong_order():
with pytest.raises(
TypeError,
match="To apply this decorator to a classmethod, apply the decorator first, then @classmethod on top.",
):
await DecoratedClass.add_classmethod_async_reverse_decorator_order(1, 2)
def test_staticmethod():
assert DecoratedClass.add_staticmethod(1, 2) == 3
assert DECORATOR_CALLED == [((1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert DecoratedClass.add_staticmethod(a=3, b=4) == 7
assert DECORATOR_CALLED == [((), {"a": 3, "b": 4})]
DECORATOR_CALLED.clear()
# Test via instance
obj = DecoratedClass(10)
assert obj.add_staticmethod(5, 6) == 11
assert DECORATOR_CALLED == [((5, 6), {})]
async def test_staticmethod_async():
assert await DecoratedClass.add_staticmethod_async(1, 2) == 3
assert DECORATOR_CALLED == [((1, 2), {})]
DECORATOR_CALLED.clear()
# Test with keyword arguments
assert await DecoratedClass.add_staticmethod_async(a=3, b=4) == 7
assert DECORATOR_CALLED == [((), {"a": 3, "b": 4})]
DECORATOR_CALLED.clear()
# Test via instance
obj = DecoratedClass(10)
assert await obj.add_staticmethod_async(5, 6) == 11
assert DECORATOR_CALLED == [((5, 6), {})]
def test_staticmethod_wrong_order():
assert DecoratedClass.add_staticmethod_reverse_decorator_order(1, 2) == 3
assert DECORATOR_CALLED == [((1, 2), {})]
async def test_staticmethod_async_wrong_order():
assert (
await DecoratedClass.add_staticmethod_async_reverse_decorator_order(1, 2) == 3
)
assert DECORATOR_CALLED == [((1, 2), {})]