Create a file or replace its content in an atomic way using tempfile.
Python, 45 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | import os
import tempfile
# This is the stupidest thing about POSIX and glibc, fixed only in Hurd: must
# change umask to be able read its value! Quantum umask!
my_umask = os.umask(0)
os.umask(my_umask)
class SafeOpen:
'''Open a file for writing using safe atomic replacement
Example usage:
with SafeOpen(fname) as f:
f.write('Hello World.\n')
'''
def __init__(self, target, mode='w', tempdir=None, prefix=None, perms=0666,
use_umask=True):
self.target = target
assert mode in ['w', 'wb'], '(re)write is the only supported open mode!'
self.mode = mode
tdir, tname = os.path.split(target)
assert tname, 'Remove slash at end of fname!'
self.tdir = tempdir or tdir or '.' # in case dirname returns '' for
# current dir...
self.prefix = prefix or ('.%s.' % tname)
self.perms = perms
if use_umask:
self.perms &= ~my_umask
def __enter__(self):
fd, self.tpath = tempfile.mkstemp(prefix=self.prefix, dir=self.tdir,
text='b' not in self.mode)
self.f = os.fdopen(fd, self.mode)
return self.f
def __exit__(self, exct, excv, exctb):
self.f.close()
if excv is None:
os.chmod(self.tpath, self.perms)
os.rename(self.tpath, self.target) # Unix only, meanless for Windows
# with no atomic replace support
else:
# an error occurred, delete the file (and reraise exc)
os.unlink(self.tpath)
return False
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