I have the following error running fcdp-tetra_demod.py

./170913/src/demod/python/fcdp-tetra_demod.py -D hw:1 -o /dev/stdout | ./170913/src/float_to_bits /dev/stdin /dev/stdout | ./170913/src/tetra-rx /dev/stdin
Traceback (most recent call last):
  File "./170913/src/demod/python/fcdp-tetra_demod.py", line 5, in <module>
    from gnuradio import gr, gru, audio, eng_notation, blks2, optfir
ImportError: cannot import name blks2