pidfile context manager

have_pidfile.py

import os
import contextmanager

@contextlib.contextmanager
def have_pidfile(fname):
    f = open(fname, 'w')
    f.write('%d\n' % os.getpid())
    f.flush()
    s = os.fstat(f.fileno())
    dev, ino = s.st_dev, s.st_ino
    try:
        yield f
    finally:
        try:
            # make sure we still own the thing linked there
            s = os.stat(fname)
            if s.st_dev == dev and s.st_ino == ino:
                # (race condition here)
                os.unlink(fname)
        except OSError:
            pass
        finally:
            f.close()