class_docstr: Abstract base class for inducing variables.
code: def __len__(self) -> tf.Tensor:
      return self.num_inducing
  
imports: import abc
  from typing import Optional
  import tensorflow
  import tensorflow_probability
  from check_shapes import Shape, check_shapes
  from deprecated import deprecated
  from ..base import Module, Parameter, TensorData, TensorType
  from ..utilities import positive
label_desc: Use image node_id 2 for calling the InducingVariables obj's underlying member method code with example usage: obj.__len__() and returns: self