import contextlib
import io
import os
import sys
import tempfile
try:
import fcntl
except ImportError:
fcntl = None
# `fspath` was added in Python 3.6
try:
from os import fspath
except ImportError:
fspath = None
__version__ = '1.4.0'
PY2 = sys.version_info[0] == 2
text_type = unicode if PY2 else str # noqa
def _path_to_unicode(x):
if not isinstance(x, text_type):
return x.decode(sys.getfilesystemencoding())
return x
DEFAULT_MODE = "wb" if PY2 else "w"
_proper_fsync = os.fsync
if sys.platform != 'win32':
if hasattr(fcntl, 'F_FULLFSYNC'):
def _proper_fsync(fd):
# https://lists.apple.com/archives/darwin-dev/2005/Feb/msg00072.html
# https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man2/fsync.2.html
# https://github.com/untitaker/python-atomicwrites/issues/6
fcntl.fcntl(fd, fcntl.F_FULLFSYNC)
def _sync_directory(directory):
# Ensure that filenames are written to disk
fd = os.open(directory, 0)
try:
_proper_fsync(fd)
finally:
os.close(fd)
def _replace_atomic(src, dst):
os.rename(src, dst)
_sync_directory(os.path.normpath(os.path.dirname(dst)))
def _move_atomic(src, dst):
os.link(src, dst)
os.unlink(src)
src_dir = os.path.normpath(os.path.dirname(src))
dst_dir = os.path.normpath(os.path.dirname(dst))
_sync_directory(dst_dir)
if src_dir != dst_dir:
_sync_directory(src_dir)
else:
from ctypes import windll, WinError
_MOVEFILE_REPLACE_EXISTING = 0x1
_MOVEFILE_WRITE_THROUGH = 0x8
_windows_default_flags = _MOVEFILE_WRITE_THROUGH
def _handle_errors(rv):
if not rv:
raise WinError()
def _replace_atomic(src, dst):
_handle_errors(windll.kernel32.MoveFileExW(
_path_to_unicode(src), _path_to_unicode(dst),
_windows_default_flags | _MOVEFILE_REPLACE_EXISTING
))
def _move_atomic(src, dst):
_handle_errors(windll.kernel32.MoveFileExW(
_path_to_unicode(src), _path_to_unicode(dst),
_windows_default_flags
))
[docs]def replace_atomic(src, dst):
'''
Move ``src`` to ``dst``. If ``dst`` exists, it will be silently
overwritten.
Both paths must reside on the same filesystem for the operation to be
atomic.
'''
return _replace_atomic(src, dst)
[docs]def move_atomic(src, dst):
'''
Move ``src`` to ``dst``. There might a timewindow where both filesystem
entries exist. If ``dst`` already exists, :py:exc:`FileExistsError` will be
raised.
Both paths must reside on the same filesystem for the operation to be
atomic.
'''
return _move_atomic(src, dst)
[docs]class AtomicWriter(object):
'''
A helper class for performing atomic writes. Usage::
with AtomicWriter(path).open() as f:
f.write(...)
:param path: The destination filepath. May or may not exist.
:param mode: The filemode for the temporary file. This defaults to `wb` in
Python 2 and `w` in Python 3.
:param overwrite: If set to false, an error is raised if ``path`` exists.
Errors are only raised after the file has been written to. Either way,
the operation is atomic.
If you need further control over the exact behavior, you are encouraged to
subclass.
'''
def __init__(self, path, mode=DEFAULT_MODE, overwrite=False,
**open_kwargs):
if 'a' in mode:
raise ValueError(
'Appending to an existing file is not supported, because that '
'would involve an expensive `copy`-operation to a temporary '
'file. Open the file in normal `w`-mode and copy explicitly '
'if that\'s what you\'re after.'
)
if 'x' in mode:
raise ValueError('Use the `overwrite`-parameter instead.')
if 'w' not in mode:
raise ValueError('AtomicWriters can only be written to.')
# Attempt to convert `path` to `str` or `bytes`
if fspath is not None:
path = fspath(path)
self._path = path
self._mode = mode
self._overwrite = overwrite
self._open_kwargs = open_kwargs
[docs] def open(self):
'''
Open the temporary file.
'''
return self._open(self.get_fileobject)
@contextlib.contextmanager
def _open(self, get_fileobject):
f = None # make sure f exists even if get_fileobject() fails
try:
success = False
with get_fileobject(**self._open_kwargs) as f:
yield f
self.sync(f)
self.commit(f)
success = True
finally:
if not success:
try:
self.rollback(f)
except Exception:
pass
[docs] def get_fileobject(self, suffix="", prefix=tempfile.gettempprefix(),
dir=None, **kwargs):
'''Return the temporary file to use.'''
if dir is None:
dir = os.path.normpath(os.path.dirname(self._path))
descriptor, name = tempfile.mkstemp(suffix=suffix, prefix=prefix,
dir=dir)
# io.open() will take either the descriptor or the name, but we need
# the name later for commit()/replace_atomic() and couldn't find a way
# to get the filename from the descriptor.
os.close(descriptor)
kwargs['mode'] = self._mode
kwargs['file'] = name
return io.open(**kwargs)
[docs] def sync(self, f):
'''responsible for clearing as many file caches as possible before
commit'''
f.flush()
_proper_fsync(f.fileno())
[docs] def commit(self, f):
'''Move the temporary file to the target location.'''
if self._overwrite:
replace_atomic(f.name, self._path)
else:
move_atomic(f.name, self._path)
[docs] def rollback(self, f):
'''Clean up all temporary resources.'''
os.unlink(f.name)
[docs]def atomic_write(path, writer_cls=AtomicWriter, **cls_kwargs):
'''
Simple atomic writes. This wraps :py:class:`AtomicWriter`::
with atomic_write(path) as f:
f.write(...)
:param path: The target path to write to.
:param writer_cls: The writer class to use. This parameter is useful if you
subclassed :py:class:`AtomicWriter` to change some behavior and want to
use that new subclass.
Additional keyword arguments are passed to the writer class. See
:py:class:`AtomicWriter`.
'''
return writer_cls(path, **cls_kwargs).open()