Traceback (most recent call last):
  File "test.py", line 23, in <module>
    tck = interpolate.splrep(x, y, t=knots, w=weights)
  File "/usr/local/lib/python2.7/dist-packages/scipy/interpolate/fitpack.py", line 515, in splrep
    raise _iermess[ier][1](_iermess[ier][0])
ValueError:     Error on input data