docstr: returns number of frames
docstr_tok: ["returns","number","of","frames"]
code: def get_nframes(self):
      """returns number of frames"""
      framed = get_frame_order(self._mlist)
      return len(framed)
  
imports: import warnings
  from numbers import Integral
  import numpy
  from .arraywriters import make_array_writer
  from .fileslice import canonical_slicers, predict_shape, slice2outax
  from .spatialimages import SpatialHeader, SpatialImage
  from .volumeutils import array_from_file, make_dt_codes, native_code, swapped_code
  from .wrapstruct import WrapStruct
label_desc: Use image node_id 3 for calling the EcatSubHeader obj's underlying member method code with example usage: obj.get_nframes() and returns: len