python-development

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
• Internal private helpers may be used across agent_framework* modules when intentional; use a targeted # pyright: ignore[reportPrivateUsage] instead of making the helper public just to satisfy pyright.
• Do not add trivial pass-through or one-line helper functions solely to appease typing. Prefer targeted ignores, casts, or clearer annotations over adding runtime overhead without a design benefit.

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 =

• 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:

• 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

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__.

Special case: the root agent_framework/__init__.py uses lazy runtime exports. For root public API changes:

• Add the symbol to _LAZY_MODULE_EXPORTS and keep _LAZY_EXPORTS derived from it.
• Keep the explicit runtime __all__ synchronized; it is still required for from agent_framework import *.
• Add the same public symbol to agent_framework/__init__.pyi so pyright, mypy, and editors see the typed surface.
• Put runtime deprecation behavior in the owning module via that module's __getattr__; avoid root-level special-case branches for individual deprecated exports.
• Identity aliases are appropriate in .pyi stubs because they mark re-exported names for type checkers; avoid them in runtime .py modules unless there is a specific compatibility reason.

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