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Handle args/kwargs appropriately for various objects

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This commit is contained in:
Jeremiah Lowin 2025-05-04 15:00:26 -04:00
commit c449f1d697
11 changed files with 188 additions and 21 deletions
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4
docs/servers/prompts.mdx
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@ -53,6 +53,9 @@ def generate_code_request(language: str, task_description: str) -> UserMessage:
* **Inferred Metadata:** By default:
* Prompt Name: Taken from the function name (`ask_about_topic`).
* Prompt Description: Taken from the function's docstring.
<Tip>
Functions with `*args` or `**kwargs` are not supported as prompts. This restriction exists because FastMCP needs to generate a complete parameter schema for the MCP protocol, which isn't possible with variable argument lists.
</Tip>
### Return Values
@ -105,6 +108,7 @@ def generate_content_request(
return prompt
```
### Required vs. Optional Parameters
Parameters in your function signature are considered **required** unless they have a default value.

4
docs/servers/resources.mdx
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@ -239,6 +239,10 @@ Resource templates share most configuration options with regular resources (name
Resource templates generate a new resource for each unique set of parameters, which means that resources can be dynamically created on-demand. For example, if the resource template `"user://profile/{name}"` is registered, MCP clients could request `"user://profile/ford"` or `"user://profile/marvin"` to retrieve either of those two user profiles as resources, without having to register each resource individually.
<Tip>
Functions with `*args` are not supported as resource templates. However, unlike tools and prompts, resource templates do support `**kwargs` because the URI template defines specific parameter names that will be collected and passed as keyword arguments.
</Tip>
Here is a complete example that shows how to define two resource templates:
```python

6
docs/servers/tools.mdx
View file

@ -43,9 +43,12 @@ When this tool is registered, FastMCP automatically:
- Generates an input schema based on the function's parameters and type annotations.
- Handles parameter validation and error reporting.
The way you define your Python function dictates how the tool appears and behaves for the LLM client.
<Tip>
Functions with `*args` or `**kwargs` are not supported as tools. This restriction exists because FastMCP needs to generate a complete parameter schema for the MCP protocol, which isn't possible with variable argument lists.
</Tip>
### Parameters
#### Annotations
@ -90,6 +93,7 @@ def process_image(
# Implementation...
```
You can also use the Field as a default value, though the Annotated approach is preferred:
```python