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SergeyMenshykh 1d94518f37 Python: Add ClassSkill for class-based skill definitions (#5678)
* Python: Add ClassSkill for class-based skill definitions

Add ClassSkill abstract base class with decorator-based resource and script
discovery, porting .NET's AgentClassSkill (PRs #5027 and #5183) to Python.

- Add ClassSkill(Skill, ABC) with instructions abstract property, cached
  content/resources/scripts properties
- Add @ClassSkill.resource and @ClassSkill.script static method decorators
  for auto-discovery of methods and properties
- Extract _build_skill_content() and _create_resource_element() shared
  helpers from InlineSkill for reuse
- Add _discover_marked_members() for scanning class hierarchies
- Add _make_method_name() for Python-to-skill name conversion
- Add class_based_skill sample (UnitConverterSkill)
- Update mixed_skills sample with TemperatureConverterSkill
- Add 58 new tests covering ClassSkill, decorator discovery, property
  resources, inheritance, kwargs forwarding, and duplicate detection
- Export ClassSkill from agent_framework public API

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: replace try/except/continue with assignment to satisfy bandit B112

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* address PR review feedback

- Walk cls.__mro__ in _discover_marked_members for inherited property resources
- Use inspect.getattr_static for MRO-aware is_property check
- Return defensive copies from resources/scripts properties
- Raise TypeError on wrong decorator stacking order (@resource above @property)
- Log warning instead of silently swallowing descriptor errors during discovery
- Validate explicit name= at decoration time via _validate_member_name
- Add tests for all of the above

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix temperature converter skill: make resource necessary for script

Refactor TemperatureConverterSkill so the agent must read the
formulas resource (factor/offset) before calling the script,
aligning with the volume-converter pattern.

- Resource: numeric factor/offset table instead of symbolic formulas
- Script: generic linear transform (value * factor + offset)
- Instructions: updated to reflect new workflow

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-05-07 19:39:12 +00:00

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4.2 KiB
Markdown

# Agent Skills Samples
These samples demonstrate how to use **Agent Skills** — modular packages of instructions, resources, and scripts that extend an agent's capabilities. Skills follow the [Agent Skills specification](https://agentskills.io/) and use progressive disclosure to optimize token usage.
## Learning Path
Start with file-based or code-defined skills, then explore combining them and adding approval workflows.
| Sample | Description |
|--------|-------------|
| [**file_based_skill**](file_based_skill/) | Define skills as `SKILL.md` files on disk with reference documents and executable scripts. Uses the unit-converter skill. |
| [**code_defined_skill**](code_defined_skill/) | Define skills entirely in Python code using `Skill`, `@skill.resource`, and `@skill.script` decorators. Uses a code-defined unit-converter skill. |
| [**class_based_skill**](class_based_skill/) | Define skills as Python classes using `ClassSkill` with `@ClassSkill.resource` and `@ClassSkill.script` decorators for auto-discovery. Uses a class-based unit-converter skill. |
| [**mixed_skills**](mixed_skills/) | Combine code-defined, class-based, and file-based skills in a single agent. Uses a code-defined volume-converter, a class-based temperature-converter, and a file-based unit-converter. |
| [**script_approval**](script_approval/) | Require human-in-the-loop approval before executing skill scripts |
## Key Concepts
### Progressive Disclosure
Skills use a three-step interaction model to minimize token usage:
1. **Advertise** — Skill names and descriptions (~100 tokens each) are injected into the system prompt
2. **Load** — Full instructions are loaded on-demand via the `load_skill` tool
3. **Access** — Resources are read via `read_skill_resource`; scripts are executed via `run_skill_script`
### File-Based vs Code-Defined vs Class-Based Skills
| Aspect | File-Based | Code-Defined | Class-Based |
|--------|-----------|--------------|-------------|
| Definition | `SKILL.md` files on disk | `Skill` instances in Python | Classes extending `ClassSkill` |
| Resources | Static files in `references/` and `assets/` directories | Callable functions via `@skill.resource` decorator | `@ClassSkill.resource` decorator (auto-discovered) |
| Scripts | Python files in `scripts/` directory (executed via subprocess) | Callable functions via `@skill.script` decorator (executed in-process) | `@ClassSkill.script` decorator (executed in-process) |
| Discovery | Automatic via `skill_paths` parameter | Explicit via `skills` parameter | Explicit via `skills` parameter |
| Dynamic content | No (static files only) | Yes (functions can generate content at runtime) | Yes (functions can generate content at runtime) |
| Sharing pattern | Copy skill directory | Inline or shared instances | Package in shared libraries/PyPI |
All three types can be combined in a single `SkillsProvider` — see the [mixed_skills](mixed_skills/) sample.
### Script Execution
Skills can include executable scripts. How a script runs depends on how it was defined:
| | Code-Defined Scripts | File-Based Scripts |
|---|---|---|
| **Defined via** | `@skill.script` decorator | `.py` files in `scripts/` directory |
| **Execution** | In-process (direct function call) | Delegated to a `script_runner` |
| **`script_runner` needed?** | No — runs in-process automatically | **Yes** — required |
The `script_runner` parameter on `SkillsProvider` is only applicable to **file-based** scripts. Code-defined scripts are always executed in-process regardless of this setting. See [file_based_skill](file_based_skill/) for an example using a `SkillScriptRunner` callable with a subprocess runner, and [code_defined_skill](code_defined_skill/) for in-process scripts that need no runner.
## Prerequisites
All samples require:
- An [Azure AI Foundry](https://ai.azure.com/) project with a deployed model (e.g. `gpt-4o-mini`)
- Azure CLI authentication (`az login`)
- Environment variables set in a `.env` file (see `python/.env.example`)
## Suppressing the experimental warning
The Agent Skills APIs in these samples are still experimental. Each sample includes
a short commented `warnings.filterwarnings(...)` snippet near the imports. Uncomment
it if you want to suppress the Skills warning before using the experimental APIs.