start/stop test with UHD src and file sink only

gistfile1.txt

#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: Uhdrx Filesink
# Generated: Mon Dec 16 14:23:53 2013
#
# to use: watch -n1 'ls -l rx_out' # in another terminal
##################################################

from gnuradio import blocks
from gnuradio import eng_notation
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 time

class uhdrx_filesink(gr.top_block):

    def __init__(self):
        gr.top_block.__init__(self, "Uhdrx Filesink")

        ##################################################
        # 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(25, 0)
        self.blocks_file_sink_0 = blocks.file_sink(gr.sizeof_gr_complex*1, "rx_out", False)
        self.blocks_file_sink_0.set_unbuffered(False)

        ##################################################
        # Connections
        ##################################################
        self.connect((self.uhd_usrp_source_0, 0), (self.blocks_file_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 = uhdrx_filesink()
    tb.start()
    running = True

    while (1):
        if running:
            s = raw_input('Enter stop: ')
        else:
            s = raw_input('Enter start: ')
        if (len(s) == 0):
            if running:
                tb.stop()
                tb.wait()
                running = False
            else:
                tb.start()
                running = True