atomicwrites 0.1.5

Atomic file writes.

Atomic file writes.

from atomicwrites import atomic_write

with atomic_write('foo.txt', overwrite=True) as f:
    f.write('Hello world.')
    # "foo.txt" doesn't exist yet.

# Now it does.

Features that distinguish it from other similar libraries (see alternatives).

• Race-free assertion that the target file doesn’t yet exist. This can be controlled with the overwrite parameter.

• Windows support, although not well-tested. The MSDN resources are not very explicit about which operations are atomic.

• Simple high-level API that wraps a very flexible class-based API.

• Consistent error handling across platforms.

How it works

It uses a temporary file in the same directory as the given path. This ensures that the temporary file resides on the same filesystem.

The temporary file will then be atomically moved to the target location: On POSIX, it will use rename if files should be overwritten, otherwise a combination of link and unlink. On Windows, it uses MoveFileEx (see MSDN) through stdlib’s ctypes with the appropriate flags.

Note that with link and unlink, there’s a timewindow where the file might be available under two entries in the filesystem: The name of the temporary file, and the name of the target file.

Alternatives

python-atomicwrites is inspired by some of the following libraries, however, no code has been directly taken from them:

• The Trac project’s utility functions, also used in Werkzeug and mitsuhiko/python-atomicfile.

• abarnert/fatomic

• sashka/atomicfile

License

Licensed under the MIT, see LICENSE.