class_docstr: Base class used to filter attributes based on their expected class.
code: def __len__(self):
      return sum(
          map(
              lambda x: isinstance(x, self.clazz),
              self.attributes.values(),
          )
      )
  
imports: from collections.abc import MutableMapping
  from numbers import Integral
  from hls4ml.model.types import NamedType, Source, TensorVariable, WeightVariable
  from hls4ml.utils.string_utils import convert_to_pascal_case
label_desc: Use image node_id 3 for calling the AttributeMapping obj's underlying member method code with example usage: obj.__len__() and returns: sum