MoviePilot/docs/rules/06-code-styles.md

06 — Code Standards and Style

General Principles

• Preserve the style of the surrounding file. When in doubt, read neighboring code first.
• Prefer the smallest correct change. Do not introduce a new abstraction layer without a clear payoff.
• Do not add features, refactors, or abstractions beyond what the task requires.
• Do not add error handling or validation for scenarios that cannot happen. Trust internal code and framework guarantees; only validate at system boundaries (user input, external API responses).

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Python Version and Typing

• Target: Python 3.14+. Python 3.14 is the primary CI version; dependency CI also verifies supported platforms and both Linux runtime profiles.
• Type annotations are required on all public methods and function signatures.
• Use Optional[X] for nullable types (do not use X | None — keep consistency with the existing codebase style).
• Use Union[X, Y] for multi-type parameters.
• Prefer list[X], dict[K, V], tuple[X, Y] built-in generics in new code (Python 3.9+); match the style of the surrounding file.
• Use pathlib.Path for all file path operations. Never use raw string concatenation for paths.

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Pydantic Models

• All request body and response models must be defined as Pydantic BaseModel subclasses in app/schemas/.
• Use Field(...) for required fields; use Field(default=...) or Field(None) for optional fields.
• Do not define ad-hoc dict return types for API responses — define a schema class.
• Settings and deployment configuration live in ConfigModel / Settings in app/runtime/config.py using pydantic-settings.
• Use model_validator for cross-field validation logic.

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Async and Concurrency

• Prefer async def for I/O-bound operations (network requests, database queries, file operations).
• Use await consistently; do not mix sync and async code paths in the same function without using run_in_threadpool from FastAPI or asyncio.to_thread.
• For CPU-bound work that must not block the event loop, submit to ThreadHelper (see app/runtime/thread.py).
• Use ThreadHelper.submit() for finite background work. A long-lived protocol loop may use a dedicated threading.Thread only when its existing lifecycle owner signals and joins that child, while the external caller bounded-waits and retains the parent owner on non-convergence; do not create a dedicated thread pool for that exception.

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Imports

Order imports as follows, separated by blank lines:

1. Standard library (import os, import json, etc.)
2. Third-party packages (from fastapi import ..., from pydantic import ...)
3. Local application packages (from app.chain import ..., from app.schemas import ...)

Within each group, sort alphabetically. Do not use wildcard imports (from module import *) in application code.

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String Formatting

• Use f-strings for all string interpolation. Do not use % formatting or .format().
• For log messages, use logger.info(f"...") — do not use lazy %s format in logger calls (the project does not rely on lazy evaluation here).

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Error Handling

• In chain and module layers: do not raise HTTP exceptions. Catch exceptions, log them, and return None or a domain-level error object so the caller can decide how to proceed.
• In endpoint layer: use FastAPI's HTTPException or the project's standard response schemas for errors.
• Application and adapter layers must not swallow operational failures silently. Log or re-raise them according to the owning contract. Foundation primitives do not log; they return their documented fallback value or raise, leaving operational reporting to the caller.
• Do not use bare except: — always catch a specific exception type or at minimum Exception.
• logger.exception(...) records at ERROR level and includes the current traceback in console output by default. File and resource logs receive the formatted ERROR message through the usual routing. An explicit exc_info value follows standard-library logging semantics.

# Correct
try:
    result = self.do_work()
except Exception as err:
    logger.error(f"Failed to do work: {str(err)}")
    return None

# Wrong — swallowing silently
try:
    result = self.do_work()
except:
    pass

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Logging

• Host code uses logger from app.runtime.log; new plugins use app.sdk.logging. The historical app.log path is compatibility-only. Do not import the standard library logging directly in application code.
• Log levels:
  • logger.debug(...) — detailed diagnostic information, disabled by default.
  • logger.info(...) — normal operational events.
  • logger.warning(...) — unexpected but recoverable situations.
  • logger.error(...) — failures that affect functionality.
• Keep log messages in Chinese unless the surrounding file consistently uses English.

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Constants and Magic Values

• Do not scatter raw string keys for SystemConfig. Add a SystemConfigKey enum entry and reference it.
• Do not use magic numbers or magic strings inline. Define a named constant or enum value.

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File Organization

• One primary class per file is the norm for chains, modules, services, and adapters.
• Private functions in the same file are preferable to extracting a new module for single-use logic.
• Add code to the canonical capability package that owns it, and extend an existing domain file whenever that domain already exists.
• Do not recreate generic core, helper, or utils buckets; see 05-architecture.md for placement rules.
• New files use one focused lowercase noun. When the capability already names the package, put the role in a single-word child such as plugin/manager.py; do not flatten it back into plugin_manager.py.
• Keep files focused on one domain concern.

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What Not To Do

• Do not introduce new third-party libraries without placing them in the correct pyproject.toml dependency group and updating uv.lock: runtime packages belong in [project].dependencies, test/lint/build tooling in [dependency-groups].dev.
• Do not use requests or httpx directly for external HTTP calls - host code uses RequestUtils from app/adapters/network/http.py; plugins use app.sdk.network.
• Do not issue raw SQLAlchemy queries or import Oper classes from chains, modules, or endpoints. Define/consume an Application persistence Port; its concrete implementation under app/db/adapters/ may use Oper classes from app/db/oper/.
• Do not add TODO or FIXME without context. Only keep one if it is genuinely deferred and cannot be addressed in the current task.
• Do not add noisy markers like # change starts here, # important, or # this is a fix.
• Do not write comments that restate what the code already clearly says.

Last Updated: 2026-08-19