uhd RX start/stop test on top_block

gistfile1.txt

#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: Uhd Rx
# Generated: Mon Dec 16 14:05:31 2013
##################################################

from gnuradio import analog
from gnuradio import audio
from gnuradio import blocks
from gnuradio import eng_notation
from gnuradio import filter
from gnuradio import gr
from gnuradio import uhd
from gnuradio.eng_option import eng_option
from gnuradio.filter import firdes
from optparse import OptionParser
import math
import time

class uhd_rx(gr.top_block):

    def __init__(self):
        gr.top_block.__init__(self, "Uhd Rx")

        ##################################################
        # Variables
        ##################################################
        self.samp_rate = samp_rate = 160000

        ##################################################
        # Blocks
        ##################################################
        self.uhd_usrp_source_0 = uhd.usrp_source(
        	device_addr="",
        	stream_args=uhd.stream_args(
        		cpu_format="fc32",
        		channels=range(1),
        	),
        )
        self.uhd_usrp_source_0.set_samp_rate(samp_rate)
        self.uhd_usrp_source_0.set_center_freq(88.3e6, 0)
        self.uhd_usrp_source_0.set_gain(20, 0)
        self.rational_resampler_xxx_0 = filter.rational_resampler_fff(
                interpolation=3,
                decimation=10,
                taps=None,
                fractional_bw=None,
        )
        self.blocks_multiply_const_vxx_0 = blocks.multiply_const_vff((.1, ))
        self.audio_sink_0 = audio.sink(48000, "", True)
        self.analog_quadrature_demod_cf_0 = analog.quadrature_demod_cf(1)

        ##################################################
        # Connections
        ##################################################
        self.connect((self.uhd_usrp_source_0, 0), (self.analog_quadrature_demod_cf_0, 0))
        self.connect((self.analog_quadrature_demod_cf_0, 0), (self.rational_resampler_xxx_0, 0))
        self.connect((self.rational_resampler_xxx_0, 0), (self.blocks_multiply_const_vxx_0, 0))
        self.connect((self.blocks_multiply_const_vxx_0, 0), (self.audio_sink_0, 0))


# QT sink close method reimplementation

    def get_samp_rate(self):
        return self.samp_rate

    def set_samp_rate(self, samp_rate):
        self.samp_rate = samp_rate
        self.uhd_usrp_source_0.set_samp_rate(self.samp_rate)

if __name__ == '__main__':
    parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
    (options, args) = parser.parse_args()
    tb = uhd_rx()
    tb.start()
    running = True

    while (1):
        if running:
            s = raw_input('(x to exit) Enter stop: ')
        else:
            s = raw_input('(x to exit) Enter start: ')
        if (len(s) == 0):
            if running:
                tb.stop()
                tb.wait()
                running = False
            else:
                tb.start()
                running = True
        elif s == "x":
            tb.stop()
            sys.exit()