onnxruntime/docs/how-to/custom-python-operator.md

---
title: Use the PyOp operator
parent: Recipes
nav_order: 4
---

# How to use the Python Operator (PyOp)
{: .no_toc }

The Python Operator provides the capability to easily invoke any custom Python code within a single node of an ONNX graph using ONNX Runtime. This can be useful for quicker experimentation when a model requires operators that are not officially supported in ONNX and ONNX Runtime, particularly if there is already a Python implementation for the required functionality. This should be used with discretion in production scenarios, and all security or other risks should be considered beforehand.

## Design Overview

The feature can be in [language_interop_ops](https://github.com/microsoft/onnxruntime/tree/master/onnxruntime/core/language_interop_ops).

Here is a chart of calling sequence:
<pre>
onnxruntime                        python capi                         script
     |                                  |                                 |
     | ------------------------------>  |                                 |
     |       call with tensor(s)        | ------------------------------> |
     |                                  |         call with numpy(s)      | 
     |                                  |                                 | compute
     |                                  | <------------------------------ |
     | <------------------------------  |           return numpys(s)      |
     |         return tensor(s)         |                                 |
</pre>

## How to Use
### Step 1
Build onnxruntime with `--config Release --enable_language_interop_ops --build_wheel` and pip install the latest wheel file. 

### Step 2
Create an onnx model containing Python operator nodes:
```python
ad1_node = helper.make_node('Add', ['A','B'], ['S'])
mul_node = helper.make_node('Mul', ['C','D'], ['P'])
py1_node = helper.make_node(op_type = 'PyOp', #required, must be 'PyOp'
                            inputs = ['S','P'], #required
                            outputs = ['L','M','N'], #required
                            domain = 'pyopmulti_1', #required, must be unique
                            input_types = [TensorProto.FLOAT, TensorProto.FLOAT], #required
                            output_types = [TensorProto.FLOAT, TensorProto.FLOAT, TensorProto.FLOAT], #required
                            module = 'mymodule', #required
                            class_name = 'Multi_1', #required
                            compute = 'compute', #optional, 'compute' by default
                            W1 = '5', W2 = '7', W3 = '9') #optional, must all be strings
ad2_node = helper.make_node('Add', ['L','M'], ['H'])
py2_node = helper.make_node('PyOp',['H','N','E'],['O','W'], domain = 'pyopmulti_2',
                            input_types = [TensorProto.FLOAT, TensorProto.FLOAT, TensorProto.FLOAT],
                            output_types = [TensorProto.FLOAT, TensorProto.FLOAT],
                            module = 'mymodule', class_name = 'Multi_2')
sub_node = helper.make_node('Sub', ['O','W'], ['F'])
graph = helper.make_graph([ad1_node,mul_node,py1_node,ad2_node,py2_node,sub_node], 'multi_pyop_graph', [A,B,C,D,E], [F])
model = helper.make_model(graph, producer_name = 'pyop_model')
onnx.save(model, './model.onnx')
```
### Step 3
Implement mymodule.py:
```python
class Multi_1:
    def __init__(self, W1, W2, W3):
        self.W1 = int(W1)
        self.W2 = int(W2)
        self.W3 = int(W3)
    def compute(self, S, P):
        ret = S + P
        return ret + self.W1, ret + self.W2, ret + self.W3
class Multi_2:
    def compute(self, *kwargs):
        return sum(kwargs[0:-1]), sum(kwargs[1:])
```
### Step 4
Copy mymodule.py into Python sys.path, then run the model with onnxruntime python API. On Windows, please set PYTHONHOME beforehand. It should point to directory where the python is installed, such as C:\Python37 or C:\ProgramData\Anaconda3\envs\myconda1 if it is in conda.

## Supported Data Types
* TensorProto.BOOL
* TensorProto.UINT8
* TensorProto.UINT16
* TensorProto.UINT32
* TensorProto.INT16
* TensorProto.INT32
* TensorProto.FLOAT
* TensorProto.DOUBLE

## Limitations
* Inferencing and compiling environments must be installed with same version of python.
* On Windows, `--config Debug` has known issues. Please build with `--config RelWithDebInfo` if debugging symbols are needed.
* Due to Python C API restrictions, multi-threading is disabled so Python operators will run sequentially.

## Test Coverage
The operator has been tested on multiple platforms, with or without conda:

Platform | Python 3.5 | Python 3.6 | Python 3.7
----------- | ------------| -----------  | -----------
Windows | (conda) passed | (conda) passed | passed
Linux | (conda) passed | (conda) passed | passed
Mac |  (conda) passed | (conda) passed | (conda) passed

## Example
Developers could resort to PyOp during model conversion for missing operators:
```python
import os
import numpy as np
from onnx import *
from skl2onnx import convert_sklearn
from skl2onnx.common.data_types import FloatTensorType
from skl2onnx.common.utils import check_input_and_output_numbers

X = np.array([[1, 1], [2, 1], [3, 1.2], [4, 1], [5, 0.8], [6, 1]],dtype=np.single)
nmf = NMF(n_components=2, init='random', random_state=0)
W = np.array(nmf.fit_transform(X), dtype=np.single)

def calculate_sklearn_nmf_output_shapes(operator):
    check_input_and_output_numbers(operator, output_count_range=1, input_count_range=1)
    operator.outputs[0].type.shape = operator.inputs[0].type.shape

def convert_nmf(scope, operator, container):
    ws = [str(w) for w in W.flatten()]
    attrs = {'W':'|'.join(ws)}
    container.add_node(op_type='PyOp', name='nmf', inputs=['X'], outputs=['variable'],
                       op_version=10, op_domain='MyDomain', module='mymodule', class_name='MyNmf',
                       input_types=[TensorProto.FLOAT], output_types=[TensorProto.FLOAT], **attrs)

custom_shape_calculators = {type(nmf): calculate_sklearn_nmf_output_shapes}
custom_conversion_functions = {type(nmf): convert_nmf}
initial_types = [('X', FloatTensorType([6,2]))]
onx = convert_sklearn(nmf, '', initial_types, '', None, custom_conversion_functions, custom_shape_calculators)
with th open("model.onnx", "wb") as f:
    f.write(onx.SerializeToString())
```
mymodule.py:
```python
import numpy as np
class MyNmf:
    def __init__(self,W):
        A = []
        for w in W.split('|'):
            A.append(float(w))
        self.__W = np.array(A,dtype=np.single).reshape(6,2)
    def compute(self,X):
        return self.__W
```