class_docstr: Binary numpy array representation of a mask.
  
  # Arguments
      data: Mask array, with the dimensions: (num_instances, height, width)
      pad_dim: bool
code: def __len__(self):
      return len(self.data)
  
imports: from icevision.imports import *
  from icevision.utils import *
  from PIL import Image
label_desc: Use image node_id 2 for calling the MaskArray obj's underlying member method code with example usage: obj.__len__() and returns: len