code: def add_event(self, key, event):
          
          assert isinstance(key, str)
          assert isinstance(event, bytes)
          if all([char.isalnum() or char == '-' for char in key]):
              safe_key = key
          else:
              raise ValueError("Key must be alphanumeric or a dash (-):"
                               " {0}".format(key))
          safe_event = base64.encodestring(event).decode().strip()
          data = "{0}\t{1}\n".format(safe_key, safe_event)
  
          # Important to make a single atomic write here
          self._hasher.update(data.encode())
          self.f.write(data)
docs: Add an event and its corresponding key to the store.