docstr: Number of bins.
code: def num_bins(self):
      """Number of bins."""
      return int(self.shape[1])
  
imports: from __future__ import absolute_import, division, print_function
  import warnings
  import numpy
  import scipy.fftpack
  from ..processors import Processor
  from .signal import Signal, FramedSignal
label_desc: Use image node_id 2 for calling the _PropertyMixin obj's underlying member method code with example usage: obj.num_bins() and returns: int