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"""File utilities"""
import os
__all__ = ['write_atomic']
def write_atomic(fn, data, bakext=None, mode='b'):
"""Write file with rename."""
if mode not in ['', 'b', 't']:
raise ValueError("unsupported fopen mode")
# write new data to tmp file
fn2 = fn + '.new'
f = open(fn2, 'w' + mode)
f.write(data)
f.close()
# link old data to bak file
if bakext:
if bakext.find('/') >= 0:
raise ValueError("invalid bakext")
fnb = fn + bakext
try:
os.unlink(fnb)
except OSError, e:
if e.errno != errno.ENOENT:
raise
try:
os.link(fn, fnb)
except OSError, e:
if e.errno != errno.ENOENT:
raise
# atomically replace file
os.rename(fn2, fn)
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