<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _find_datastream(self, name):
 """Find and return if a datastream exists, by name."""

        for stream in self.data_streams: #search to see if this is a new datastream or a known one
            if stream.name == name:
                return stream
        return None