title: redis block until key exists
body: <p>I'm new to Redis and was wondering if there is a way to be able to <code>await</code> <code>get</code>ing a value by it's key until the key exists. Minimal code:</p>
  
  <pre><code>async def handler():
      data = await self._fetch(key)
  
  async def _fetch(key):
      return self.redis_connection.get(key)
  </code></pre>
  
  <p>As you know, if such <code>key</code> doesnt exist, it <code>return</code>'s <code>None</code>. But since in my project, <code>set</code>ing key value pair to redis takes place in another application, I want the redis_connection <code>get</code> method to block untill key exists.
  Is such expectation even valid? </p>