self.stdout_path = '/dev/stdout' not possible in Python 3 anymore

[spaceone]

Hello,

the following code worked with Python 2:

from daemon.runner import DaemonRunner, DaemonRunnerStopFailureError, DaemonRunnerStartFailureError
class Foo(DaemonRunner):
    def __init__(self):
        self.stdin_path = '/dev/stdin'
        self.stdout_path = '/dev/stdout'
        self.stderr_path = '/dev/stderr'
        DaemonRunner.__init__(self, self)
…

It crashes with Python 3:

    DaemonRunner.__init__(self, self)                             
  File "/usr/lib/python3/dist-packages/daemon/runner.py", line 111, in __init__
    self.daemon_context.stdout = open(app.stdout_path, 'w+t')
io.UnsupportedOperation: File or stream is not seekable.

How do I get it working again?

[spaceone]

we replaced python-daemon with systemd meanwhile