ImportError: No module named 'gnuradio'

As a beginner I'm trying Coding in Python GNU Radio Applications. When I set the following code in the editor (Eclipse)

from gnuradio import gr
from gnuradio import audio, analog

class my_top_block(gr.top_block):
    def __init__(self):
        gr.top_block.__init__(self)

        sample_rate = 32000
        ampl = 0.1

        src0 = analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, 350, ampl)
        src1 = analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, 440, ampl)
        dst = audio.sink(sample_rate, "")
        self.connect(src0, (dst, 0))
        self.connect(src1, (dst, 1))

if __name__ == '__main__':
    try:
        my_top_block().run()
    except [[KeyboardInterrupt]]:
        pass

It show the following error:

   **from gnuradio import gr

ImportError: No module named 'gnuradio':**

Any help will be really appreciated ?