python-atomicwrites
Port variant py39
Summary Atomic file writes (3.9)
Package version 1.4.0
Homepage https://github.com/untitaker/python-atomicwrites
Keywords python
Maintainer Python Automaton
License Not yet specified
Other variants py310
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Last modified 20 NOV 2021, 04:14:38 UTC
Port created 12 OCT 2018, 03:30:34 UTC
Subpackage Descriptions
single =================== python-atomicwrites =================== Atomic file writes. .. code-block:: python 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 and Credit`_): - 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. I'm basing my assumptions off [a comment ] by [Doug Crook ], who appears to be a Microsoft employee: FAQ: Is MoveFileEx atomic Frequently asked question: Is MoveFileEx atomic if the existing and new files are both on the same drive? The simple answer is "usually, but in some cases it will silently fall-back to a non-atomic method, so don't count on it". The implementation of MoveFileEx looks something like this: [...] The problem is if the rename fails, you might end up with a CopyFile, which is definitely not atomic. If you really need atomic-or-nothing, you can try calling NtSetInformationFile, which is unsupported but is much more likely to be 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_ 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. Also note that the permissions of the target file may change this way. In some situations a chmod can be issued without any concurrency problems, but since that is not always the case, this library doesn't do it by itself. .. _MoveFileEx: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365240%28v=vs.85%29.aspx fsync ----- On POSIX, fsync is invoked on the temporary file after it is written (to flush file content and metadata), and on the parent directory after the file is moved (to flush filename). fsync does not take care of disks' internal buffers, but there don't seem to be any standard POSIX APIs for that. On OS X, fcntl is used with F_FULLFSYNC instead of fsync for that reason. On Windows, [_commit] is used, but there are no guarantees about disk internal buffers. Alternatives and Credit ======================= Atomicwrites is directly inspired by the following libraries (and shares a minimal amount of code):
Configuration Switches (platform-specific settings discarded)
PY310 OFF Build using Python 3.10 PY39 ON Build using Python 3.9
Package Dependencies by Type
Build (only) python-pip:single:py39
autoselect-python:single:standard
Build and Runtime python39:single:standard
Download groups
main mirror://PYPIWHL/2c/a0/da5f49008ec6e9a658dbf5d7310a4debd397bce0b4db03cf8a410066bb87
Distribution File Information
6d1784dea7c0c8d4a5172b6c620f40b6e4cbfdf96d783691f2e1302a7b88e197 6790 atomicwrites-1.4.0-py2.py3-none-any.whl
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