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Context manager to atomically replace a file (Python recipe) by Oren Tirosh
ActiveState Code (http://code.activestate.com/recipes/578166/)

This context manager ensures that a file's content is either replaced atomically with new contents or left unchanged. An exception or other error will not leave it empty or with partial content.

Python, 15 lines
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from contextlib import contextmanager
import os, binascii

@contextmanager
def replacefile(name):
    tmpname = '%s.tmp-%s' % (name, binascii.hexlify(os.urandom(10)).decode('ascii'))
    try:
        with open(tmpname, 'w+') as f:
            yield f
        os.rename(tmpname, name)
    finally:
        try:
            os.unlink(tmpname)
        except OSError:
            pass

Using this context manager is similar to using open() in a 'with' statement:

with replacefile(filename) as f:
    f.write(...)

You can safely read and write the same file name to process it in-place:

with open(filename) as fin, replacefile(filename) as fout:
    fout.write(something(fin.read()))

This context manager depends on POSIX semantics for atomically replacing a file with rename(2). Do not use this on Windows.

Tags: atomic, contextmanager, file, replace