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53 lines
1.8 KiB
Python
53 lines
1.8 KiB
Python
# Based on http://stackoverflow.com/questions/2333872/atomic-writing-to-file-with-python
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import os
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from contextlib import contextmanager
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# We would ideally atomically replace any existing file with the new
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# version. However, on Windows there's no Python-only solution prior
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# to Python 3.3. (This library includes a C extension to do so:
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# https://pypi.python.org/pypi/pyosreplace/0.1.)
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#
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# Correspondingly, we make a best effort, but on Python < 3.3 use a
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# replace method which could result in the file temporarily
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# disappearing.
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import sys
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if sys.version_info >= (3, 3):
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# Python 3.3 and up have a native `replace` method
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from os import replace
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elif sys.platform.startswith("win"):
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def replace(src, dst):
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# TODO: on Windows, this will raise if the file is in use,
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# which is possible. We'll need to make this more robust over
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# time.
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os.remove(dst)
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os.rename(src, dst)
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else:
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# POSIX rename() is always atomic
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from os import rename as replace
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@contextmanager
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def atomic_write(filepath, binary=False, fsync=False):
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""" Writeable file object that atomically updates a file (using a temporary file). In some cases (namely Python < 3.3 on Windows), this could result in an existing file being temporarily unlinked.
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:param filepath: the file path to be opened
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:param binary: whether to open the file in a binary mode instead of textual
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:param fsync: whether to force write the file to disk
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"""
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tmppath = filepath + '~'
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while os.path.isfile(tmppath):
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tmppath += '~'
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try:
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with open(tmppath, 'wb' if binary else 'w') as file:
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yield file
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if fsync:
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file.flush()
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os.fsync(file.fileno())
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replace(tmppath, filepath)
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finally:
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try:
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os.remove(tmppath)
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except (IOError, OSError):
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pass
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