python-development

name	python-development
description	Coding standards, conventions, and patterns for developing Python code in the Agent Framework repository. Use this when writing or modifying Python source files in the python/ directory.

Python Development Standards

File Header

Every .py file must start with:

# Copyright (c) Microsoft. All rights reserved.

Type Annotations

• Always specify return types and parameter types
• Use Type | None instead of Optional[Type]
• Use from __future__ import annotations to enable postponed evaluation
• Use suffix T for TypeVar names: ChatResponseT = TypeVar("ChatResponseT", bound=ChatResponse)
• Use Mapping instead of MutableMapping for read-only input parameters
• Prefer # type: ignore[...] over unnecessary casts, or isinstance checks, when these are internally called and executed methods But make sure the ignore is specific for both mypy and pyright so that we don't miss other mistakes

Function Parameters

• Positional parameters: up to 3 fully expected parameters
• Use keyword-only arguments (after *) for optional parameters
• Provide string-based overrides to avoid requiring extra imports:

def create_agent(name: str, tool_mode: Literal['auto', 'required', 'none'] | ChatToolMode) -> Agent:
    if isinstance(tool_mode, str):
        tool_mode = ChatToolMode(tool_mode)

• Avoid shadowing built-ins (use next_handler instead of next)
• Avoid **kwargs unless needed for subclass extensibility; prefer named parameters

Docstrings

Use Google-style docstrings for all public APIs:

def equal(arg1: str, arg2: str) -> bool:
    """Compares two strings and returns True if they are the same.

    Args:
        arg1: The first string to compare.
        arg2: The second string to compare.

    Returns:
        True if the strings are the same, False otherwise.

    Raises:
        ValueError: If one of the strings is empty.
    """

• Always document Agent Framework specific exceptions
• Explicitly use Keyword Args when applicable
• Only document standard Python exceptions when the condition is non-obvious

Import Structure

# Core
from agent_framework import Agent, Message, tool

# Components
from agent_framework.observability import enable_instrumentation

# Connectors (lazy-loaded)
from agent_framework.openai import OpenAIChatClient
from agent_framework.foundry import FoundryChatClient

Public API and Exports

In __init__.py files that define package-level public APIs, use direct re-export imports plus an explicit __all__. Avoid identity aliases like from ._agents import Agent as Agent, and avoid from module import *.

Do not define __all__ in internal non-__init__.py modules. Exception: modules intentionally exposed as a public import surface (for example, agent_framework.observability) should define __all__.

__all__ = ["Agent", "Message", "ChatResponse"]

from ._agents import Agent
from ._types import Message, ChatResponse

Performance Guidelines

• Cache expensive computations (e.g., JSON schema generation)
• Prefer match/case on .type attribute over isinstance() in hot paths
• Avoid redundant serialization — compute once, reuse

Style

• Line length: 120 characters
• Format only files you changed, not the entire codebase
• Prefer attributes over inheritance when parameters are mostly the same
• Async by default — assume everything is asynchronous

Naming Conventions for Connectors

• _prepare_<object>_for_<purpose> for methods that prepare data for external services
• _parse_<object>_from_<source> for methods that process data from external services