title: Python subprocess wait until specific string on stdout
body: <p>I have a subprocess I start via <code>subprocess.Popen</code>. This process never exits until I send a SIGINT. I want to block the execution since a specific string is available on the stdout of the subprocess (lets say <code>foo</code>). Is there any "easy" way without create threads and queues? Something like
  <code>myprocess.wait_until("foo")</code>?</p>