# Python Plugin Filter Reading Info from Python Plugin Source
**URL:** https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651
**Category:** Development
**Tags:** python
**Created:** [July 20, 2021, 3:48am UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651 "2021-07-20T03:48:04Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 20, 2021, 3:48am UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/1 "2021-07-20T03:48:04Z")
I’m using Paraview 5.8.0 on Ubuntu 20.04.
I’ve created a python plugin that acts as a source with two vtkPolyData outputs (spheres). The source is called “CR3BP System” and inherits the VTKPythonAlgorithmBase class
```auto
class PythonCR3BPSystemSource(VTKPythonAlgorithmBase):
```
I’ve added a slider bar to the GUI for a parameter “mu” that determines the placement of the two spheres. I would like to create another source called “CR3BP Traj” that reads in the “mu” parameter from the CR3BP system. How can I go about doing this?
My first idea is to create a filter with one input and define the expected input as the “CR3BP System”. I’m not sure how to do this.
Here’s my current code for the"CR3BP System" object
```auto
from vtkmodules.vtkCommonDataModel import vtkDataSet
from vtkmodules.util.vtkAlgorithm import VTKPythonAlgorithmBase
from vtkmodules.numpy_interface import dataset_adapter as dsa
from paraview.util.vtkAlgorithm import smproxy , smproperty , smdomain
import numpy as np
# mu = 1
# to add a source, instead of a filter, use the ‘smproxy.source‘ decorator.
@smproxy.source(label="CR3BP System")
class PythonCR3BPSystemSource(VTKPythonAlgorithmBase):
def __init__ (self):
VTKPythonAlgorithmBase. __init__ (self,
nInputPorts=0,
nOutputPorts=2,
outputType='vtkPolyData')
from vtkmodules.vtkFiltersSources import vtkSphereSource
self.prim = vtkSphereSource()
self.prim.SetThetaResolution(20)
self.prim.SetPhiResolution(20)
self.prim.SetStartTheta(1e-5)
self.sec = vtkSphereSource()
self.sec.SetThetaResolution(20)
self.sec.SetPhiResolution(20)
self.sec.SetStartTheta(1e-5)
def RequestData(self, request , inInfo , outInfo):
from vtkmodules.vtkCommonDataModel import vtkPolyData
self.prim.Update()
self.sec.Update()
output0 = vtkPolyData.GetData(outInfo , 0)
output0.ShallowCopy(self.prim.GetOutput())
output1 = vtkPolyData.GetData(outInfo , 1)
output1.ShallowCopy(self.sec.GetOutput())
return 1
@smproperty.doublevector(name="mu", default_values=2.528017682687079e-05)
@smdomain.doublerange(min=0, max=0.5)
def SetMu(self, mu):
self.mu = mu
self.sec.SetCenter(1-mu,0,0)
self.prim.SetCenter(-mu,0,0)
self.Modified()
@smproperty.doublevector(name="R1", default_values=0.1041737445984205)
def SetPrimRadius(self, R1):
self.prim.SetRadius(R1)
self.Modified()
@smproperty.doublevector(name="R2", default_values=0.0023257338697660556)
def SetSecRadius(self, R2):
self.sec.SetRadius(R2)
self.Modified()
```
---
### Author:  [@lhofmann](https://discourse.paraview.org/u/lhofmann)
#### Post date: [July 20, 2021, 8:30am UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/2 "2021-07-20T08:30:09Z")
You could attach mu as a FieldData array to your output and read it in the second filter from its input.
---
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 20, 2021, 3:10pm UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/3 "2021-07-20T15:10:49Z")
Thanks! That works for me. I’ve attached my code change below.
```auto
def RequestData(self, request , inInfo , outInfo):
from vtkmodules.vtkCommonDataModel import vtkPolyData, vtkFieldData
from vtkmodules.vtkCommonCore import vtkDoubleArray
# from vtkmodules.vtkCommonDataModel import *
data = vtkDoubleArray()
data.SetNumberOfComponents(1)
data.SetNumberOfTuples(1)
data.SetName("mu")
data.SetComponent(0,0,42)
field = vtkFieldData()
field.AddArray(data)
self.prim.Update()
self.sec.Update()
output0 = vtkPolyData.GetData(outInfo , 0)
output0.ShallowCopy(self.prim.GetOutput())
output0.SetFieldData(field)
```
As a followup question, this field data is assigned to one of the sphere objects, not the CR3BPSystem object. Could I add the fielddata to the CR3BPSystem object and have that be the input to my filter? I’m going to have other parameters associated with both spheres that I want to pass on.
---
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 20, 2021, 3:52pm UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/4 "2021-07-20T15:52:03Z")
Answering my own question, I could make a multiBlockDataSet that has the spheres as blocks. I’ll try that.
---
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 20, 2021, 8:25pm UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/5 "2021-07-20T20:25:35Z")
OK, my MultiBlockDataSet looks great. I can animate the spheres moving around each other.
Now I would like to create a new source that reads in the FieldData and outputs a new PolyLineSource(). I’m getting stuck reading in the MultiBlockDataSet.
I’ve tried creating the following source from the example filter that keeps the input type
```auto
from vtkmodules.vtkCommonDataModel import vtkDataSet
from vtkmodules.util.vtkAlgorithm import VTKPythonAlgorithmBase
from vtkmodules.numpy_interface import dataset_adapter as dsa
from paraview.util.vtkAlgorithm import smproxy , smproperty , smdomain
import numpy as np
@smproxy.source(label="CR3BP Traj")
@smproperty.input(name="Input")
@smdomain.datatype(dataTypes=["vtkMultiBlockDataSet"], composite_data_supported=True)
class PreserveInputTypeFilter(VTKPythonAlgorithmBase):
"""
Example filter demonstrating how to write a filter that preserves the input
dataset type.
"""
def __init__ (self):
VTKPythonAlgorithmBase. __init__ (self,
nInputPorts=1,
nOutputPorts=1,
outputType='vtkMultiBlockDataSet')
def RequestData(self, request, inInfo, outInfo):
input0 = dsa.WrapDataObject(vtkDataSet.GetData(inInfo[0]))
inData = self.GetInputData(inInfo, 0, 0)
outData = self.GetOutputData(outInfo, 0)
print("input type =", inData.GetClassName())
print("output type =", outData.GetClassName())
assert outData.IsA(inData.GetClassName())
return 1
```
I create a CR3BPSystem object, select it, then try to create this CR3BPTraj object. I get the following errors
```auto
Input port 0 of algorithm vtkPythonAlgorithm(0x9a3b240) has 0 connections but is not optional.
ERROR: In /home/buildslave/dashboards/buildbot/paraview-pvbinsdash-linux-shared-release_superbuild/build/superbuild/paraview/src/VTK/Common/ExecutionModel/vtkDemandDrivenPipeline.cxx, line 668
vtkPVCompositeDataPipeline (0x9ed5260): Input port 0 of algorithm vtkPythonAlgorithm(0x9a3b240) has 0 connections but is not optional.
Algorithm vtkPVGeometryFilter(0xbd369c0) returned failure for request: vtkInformation (0xbd344b0) Debug: Off Modified Time: 1792682 Reference Count: 1 Registered Events: (none) Request: REQUEST_DATA_OBJECT FROM_OUTPUT_PORT: 0 ALGORITHM_AFTER_FORWARD: 1 FORWARD_DIRECTION: 0
ERROR: In /home/buildslave/dashboards/buildbot/paraview-pvbinsdash-linux-shared-release_superbuild/build/superbuild/paraview/src/VTK/Common/ExecutionModel/vtkExecutive.cxx, line 753
vtkCompositeDataPipeline (0xc006ce0): Algorithm vtkPVGeometryFilter(0xbd369c0) returned failure for request: vtkInformation (0xbd344b0)
Debug: Off
Modified Time: 1792682
Reference Count: 1
Registered Events: (none)
Request: REQUEST_DATA_OBJECT
FROM_OUTPUT_PORT: 0
ALGORITHM_AFTER_FORWARD: 1
FORWARD_DIRECTION: 0
```
---
### Author:  [@lhofmann](https://discourse.paraview.org/u/lhofmann)
#### Post date: [July 21, 2021, 7:23am UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/6 "2021-07-21T07:23:15Z")
vtkMultiBlockDataSet is not derived from vtkDataSet, so you probably need these adjustments:
- set `inputType='vtkMultiBlockDataSet'` in your `VTKPythonAlgorithmBase. __init__ ` call (it defaults to vtkDataSet)
- use `vtkMultiBlockDataSet.GetData(inInfo[0])` in RequestData
---
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 21, 2021, 2:37pm UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/7 "2021-07-21T14:37:13Z")
I’m still getting the same error. I’ve pared down my code to the bare minimum.
```auto
from vtkmodules.vtkCommonDataModel import vtkDataSet
from vtkmodules.util.vtkAlgorithm import VTKPythonAlgorithmBase
from vtkmodules.numpy_interface import dataset_adapter as dsa
from paraview.util.vtkAlgorithm import smproxy , smproperty , smdomain
import numpy as np
@smproxy.source(label="CR3BP Traj")
@smproperty.input(name="Input")
# @smdomain.datatype(dataTypes=["vtkMultiBlockDataSet"], composite_data_supported=True)
class PythonCR3BPTrajSource(VTKPythonAlgorithmBase):
def __init__ (self):
VTKPythonAlgorithmBase. __init__ (self,
nInputPorts=1,
inputType='vtkMultiBlockDataSet',
nOutputPorts=1,
outputType='vtkMultiBlockDataSet')
def RequestData(self, request, inInfo, outInfo):
input0 = vtkMultiBlockDataSet.GetData(inInfo[0])
input1 = dsa.WrapDataObject(vtkMultiBlockDataSet.GetData(inInfo[0]))
input2 = self.GetInputData(inInfo, 0, 0)
return 1
```
```auto
Input port 0 of algorithm vtkPythonAlgorithm(0x7f1454010af0) has 0 connections but is not optional.
ERROR: In /home/buildslave/dashboards/buildbot/paraview-pvbinsdash-linux-shared-release_superbuild/build/superbuild/paraview/src/VTK/Common/ExecutionModel/vtkDemandDrivenPipeline.cxx, line 668
vtkPVCompositeDataPipeline (0xa2cbc90): Input port 0 of algorithm vtkPythonAlgorithm(0x7f1454010af0) has 0 connections but is not optional.
```
---
### Author:  [@Jared\_Blanchard](https://discourse.paraview.org/u/Jared_Blanchard)
#### Post date: [July 23, 2021, 2:57am UTC](https://discourse.paraview.org/t/python-plugin-filter-reading-info-from-python-plugin-source/7651/8 "2021-07-23T02:57:33Z")
This is what ended up working
```auto
from vtkmodules.vtkCommonDataModel import vtkDataSet
from vtkmodules.util.vtkAlgorithm import VTKPythonAlgorithmBase
from vtkmodules.numpy_interface import dataset_adapter as dsa
from paraview.util.vtkAlgorithm import smproxy , smproperty , smdomain
import numpy as np
@smproxy.filter(name="CR3BP Traj")
@smproperty.input(name="Input")
@smdomain.datatype(dataTypes=["vtkMultiBlockDataSet"], composite_data_supported=True)
class PythonCR3BPTrajSource(VTKPythonAlgorithmBase):
"""
Example filter demonstrating how to write a filter that preserves the input
dataset type.
"""
def __init__ (self):
super(). __init__ (nInputPorts=1, inputType="vtkMultiBlockDataSet", nOutputPorts=1, outputType="vtkMultiBlockDataSet")
from vtkmodules.vtkFiltersSources import vtkPolyLineSource
def RequestData(self, request, inInfo, outInfo):
inData = self.GetInputData(inInfo, 0, 0)
self.mu = inData.GetFieldData().GetArray('mu').GetComponent(0,0)
print(self.mu)
return 1
```