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# Copyright (C) 2012 Codethink Limited
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
import logging
import os
import tempfile
class SaveFile(file):
'''Save files with a temporary name and rename when they're ready.
This class acts exactly like the normal ``file`` class, except that
it is meant only for saving data to files. The data is written to
a temporary file, which gets renamed to the target name when the
open file is closed. This avoids readers of the file from getting
an incomplete file.
Example:
f = SaveFile('foo', 'w')
f.write(stuff)
f.close()
The file will be called something like ``tmpCAFEBEEF`` until ``close``
is called, at which point it gets renamed to ``foo``.
If the writer decides the file is not worth saving, they can call the
``abort`` method, which deletes the temporary file.
'''
def __init__(self, filename, *args, **kwargs):
self.real_filename = filename
dirname = os.path.dirname(filename)
fd, self._savefile_tempname = tempfile.mkstemp(dir=dirname)
os.close(fd)
file.__init__(self, self._savefile_tempname, *args, **kwargs)
def abort(self):
'''Abort file saving.
The temporary file will be removed, and the universe is almost
exactly as if the file save had never started.
'''
os.remove(self._savefile_tempname)
return file.close(self)
def close(self):
ret = file.close(self)
logging.debug('Rename temporary file %s to %s' %
(self._savefile_tempname, self.real_filename))
os.rename(self._savefile_tempname, self.real_filename)
return ret
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