Atomic Writes for Home Assistant

Common errors

• ModuleNotFoundError: No module named 'atomicwrites_homeassistant'

  cause The 'atomicwrites-homeassistant' package is not installed in the Python environment.
  fix Install the package using pip: 'pip install atomicwrites-homeassistant'.

• ImportError: cannot import name 'atomic_write' from 'atomicwrites_homeassistant'

  cause The module is named 'atomicwrites', not 'atomicwrites_homeassistant'.
  fix Use the correct import statement: 'from atomicwrites import atomic_write'.

• ModuleNotFoundError: No module named 'sqlalchemy'

  cause The 'sqlalchemy' package is not installed, which is a dependency for some components.
  fix Install the package using pip: 'pip install sqlalchemy'.

• ERROR: Could not install packages due to an OSError: [Errno 13] Permission denied: 'RECORD'

  cause Insufficient permissions to write to the installation directory.
  fix Run the installation command with elevated privileges: 'sudo pip install homeassistant'.

• ModuleNotFoundError: No module named '_sqlite3'

  cause The Python installation lacks the SQLite module, which is required for database operations.
  fix Reinstall Python ensuring that the SQLite development headers are present during compilation.

Warnings

• gotcha The `atomicwrites-homeassistant` package is a fork created because the original `atomicwrites` library was unmaintained. Users should be aware they are using this Home Assistant-specific fork, which provides continued maintenance.
  Fix: Ensure you are installing `atomicwrites-homeassistant` when intending to use the Home Assistant-maintained version.
• gotcha On Windows, the atomicity guarantee for file moves (using `MoveFileEx` via `ctypes`) is not absolute; it may silently fall back to a non-atomic method in some cases. If strict atomicity is critical on Windows, additional safeguards or alternative methods may be required.
  Fix: Do not solely rely on the library for guaranteed atomicity on Windows without additional validation or error handling for critical operations. Consider alternative strategies if absolute atomicity is a must-have.
• gotcha When running Home Assistant in Docker and using individually bind-mounted configuration files (e.g., for automations or scripts), atomic writes can lead to an `OSError: [Errno 16] Resource busy`. This prevents UI editors from saving changes to these files.
  Fix: To resolve this, avoid bind-mounting individual configuration files. Instead, bind-mount the parent directory (e.g., `/config`) or use Docker volumes. Alternatively, edit these files directly on the host or accept that UI editing will not work for bind-mounted files.
• gotcha On POSIX systems, there is a small time window during `link` and `unlink` operations where the file might be accessible under both its temporary name and the target name. Additionally, file permissions of the target file may change and are not automatically preserved by the library due to concurrency concerns.
  Fix: Be aware of potential dual file entries during a brief transition period. If preserving specific permissions is crucial, implement explicit `chmod` calls after the atomic write, considering concurrency implications.

Install

• pip install atomicwrites-homeassistant Install via pip

Imports

• atomic_write

  from atomicwrites import atomic_write

Quickstart

This example demonstrates how to use `atomic_write` as a context manager to ensure that file writing is an atomic operation. The `overwrite=True` parameter ensures that if the file already exists, it will be safely replaced.

from atomicwrites import atomic_write

file_path = 'my_atomic_file.txt'
content = 'Hello, atomic world!'

# Perform an atomic write, overwriting if the file exists
with atomic_write(file_path, overwrite=True) as f:
    f.write(content)

print(f"Content written to {file_path} atomically.")