Extending Model Optimizer for Custom MXNet* Operations

This section provides instruction on how to support a custom MXNet operation (or as it called in the MXNet documentation "operator" or "layer") which is not a part of the MXNet operation set. For example, if the operator is implemented using the following guide.

This section describes a procedure on how to extract operator attributes in the Model Optimizer. The rest of the operation enabling pipeline and documentation on how to support MXNet operations from standard MXNet operation set is described in the main document Customize_Model_Optimizer.

Writing Extractor for Custom MXNet Operation

Custom MXNet operations have an attribute op (defining the type of the operation) equal to Custom and attribute op_type which is an operation type defined by an user. Implement extractor class inherited from the MXNetCustomFrontExtractorOp class instead of FrontExtractorOp class used for standard framework operations in order to extract attributes for such kind of operations. The op class attribute value should be set to the op_type value so the extractor is triggered for this kind of operation.

There is the example of the extractor for the custom operation registered with type (op_type value) equal to MyCustomOp having attribute my_attribute of the floating point type with default value 5.6. In this sample we assume that we have already created the CustomOp class (inherited from Op class) for the Model Optimizer operation for this MXNet custom operation as described in the Customize_Model_Optimizer.

from extension.ops.custom_op import CustomOp  # implementation of the MO operation class
from mo.front.mxnet.extractors.utils import get_mxnet_layer_attrs
from mo.front.extractor import MXNetCustomFrontExtractorOp
 
class CustomProposalFrontExtractor(MXNetCustomFrontExtractorOp):  # inherit from specific base class
    op = 'MyCustomOp'  # the value corresponding to the `op_type` value of the MXNet operation
    enabled = True  # the extractor is enabled
 
    @staticmethod
    def extract(node):
        attrs = get_mxnet_layer_attrs(node.symbol_dict)  # parse the attributes to a dictionary with string values
        node_attrs = {
            'my_attribute': attrs.float('my_attribute', 5.6)
        }
 
        CustomOp.update_node_stat(node, node_attrs)  # update the attributes of the node
        return self.enabled