<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_trace(host=None, port=None, patch_stdstreams=False):
 """ Opens a remote PDB on first available port. """

    if host is None:
        host = os.environ.get('REMOTE_PDB_HOST', '127.0.0.1')
    if port is None:
        port = int(os.environ.get('REMOTE_PDB_PORT', '0'))
    rdb = RemotePdb(host=host, port=port, patch_stdstreams=patch_stdstreams)
    rdb.set_trace(frame=sys._getframe().f_back)