# why some filters require UpdatePipeline and other no?
**URL:** https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244
**Category:** ParaView Support
**Created:** [October 14, 2025, 1:22pm UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244 "2025-10-14T13:22:52Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@otaolafr](https://discourse.paraview.org/u/otaolafr)
#### Post date: [October 14, 2025, 1:22pm UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/1 "2025-10-14T13:22:52Z")
hello,
i am curious about this,
i am reading a tiff file, using:
`smalltif = TIFFSeriesReader(registrationName=pathForTiffFile.split('/')[-1].replace('.tif',''), FileNames=[pathForTiffFile])`
then i am doing a median:
```auto
median1 = Median(registrationName='Median1', Input=smalltif, KernelSize = [4, 4, 4])
```
the thing is, that if i try to ‘display’ using the eye (or fetch the data from median) paraview crashes without any message or any output in the terminal.
on the contrary, if i use transform filter for example, there is no issue at all:
```python
transform2 = Transform(registrationName='Transform2', Input=smalltif)
transform2.Transform.Translate = [10.0, 0.0, 0.0]
```
so, if i do:
- import +median+visualize median directly/fetch data from median filter, paraview crashes.
- import+transform+visualize transform directly/fetch data from transform filter, paraview does it without trouble.
- import+UpdatePipeline()+median+visualize median directly/fetch data from median filter, paraview does it without trouble.
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 15, 2025, 8:30am UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/2 "2025-10-15T08:30:04Z")
> that if i try to ‘display’ using the eye (or fetch the data from median) paraview crashes without any message or any output in the terminal.
Being able to click the eye here is a bug and should not be available. You always need to press apply before clicking the eye. Does that fixes the issue ?
---
### Author:  [@otaolafr](https://discourse.paraview.org/u/otaolafr)
#### Post date: [October 15, 2025, 8:38am UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/3 "2025-10-15T08:38:26Z")
Hello Mathieu,
Yes but it was more of a question in regards to the python side of things not the gui. On why , or how to know, when the UpdatePipeline() it is necessary and when not. As in my previous example, the transform filter does its job normally while the median makes paraview crash (without any error at all)
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 15, 2025, 8:43am UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/4 "2025-10-15T08:43:27Z")
> [@otaolafr](#):
>
> to the python side of things not the gui. On why , or how to know, when the UpdatePipeline() it is necessary and when not.
please share a python script that crashes with `Median`. It should not.
---
### Author:  [@otaolafr](https://discourse.paraview.org/u/otaolafr)
#### Post date: [October 15, 2025, 9:04am UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/5 "2025-10-15T09:04:50Z")
```auto
from paraview.simple import *
from paraview.servermanager import *
from paraview.vtk.numpy_interface import dataset_adapter as dsa
spruce_smalltif = TIFFSeriesReader(registrationName='spruce_small.tif', FileNames=['/home/franco/Downloads/spruce_small.tif'])
#UpdatePipeline()
median1 = Median(registrationName='Median', Input=spruce_smalltif, KernelSize = [1,1,1])
transform2 = Transform(registrationName='Transform2', Input=spruce_smalltif)
transform2.Transform.Translate = [10.0, 0.0, 0.0]
data=dsa.WrapDataObject(servermanager.Fetch(median1))
```
it crashes when the fetch is called to be exact, where if i fetch the data from transform2 it does not.
here you have the data if necessary [FileSender](https://filesender.renater.fr/?s=download&token=7debf4bb-5d93-47fe-b0af-4db6c6ced398) but doubt that it is the data itself the issue.
adding the `UpdatePipeline()` BEFORE the median filter solves the crash (after the median filter it still crashes.)
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 15, 2025, 1:38pm UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/6 "2025-10-15T13:38:33Z")
Hi @otaolafr
There is a bug in `vtkImageMedian3D` where it does not check that an array has been set before accessing it which causes the segfault. However, adding the check would just mean that ParaView would error out instead.
Indeed, calling `Fetch()` an a non-updated pipeline is not supported. It could be supported but it currently is not. Always `UpdatePipeline` before `Fetch`.
---
### Author:  [@otaolafr](https://discourse.paraview.org/u/otaolafr)
#### Post date: [October 15, 2025, 1:51pm UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/7 "2025-10-15T13:51:29Z")
> [@mwestphal](#):
>
> There is a bug in `vtkImageMedian3D` where it does not check that an array has been set before accessing it which causes the segfault. However, adding the check would just mean that ParaView would error out instead.
well, and how does it that with transform it does not give any error?
> Indeed, calling `Fetch()` an a non-updated pipeline is not supported. It could be supported but it currently is not. Always `UpdatePipeline` before `Fetch`.
in my case I simply put it inside the function i use to fetch the data (i have a function that calls fetch inside of it), but would be awsome if when fetch is called updatePipeline is called also, as it is a necessary thing and it would reduce for other users that will not know this.
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 15, 2025, 1:54pm UTC](https://discourse.paraview.org/t/why-some-filters-require-updatepipeline-and-other-no/17244/8 "2025-10-15T13:54:45Z")
> [@otaolafr](#):
>
> well, and how does it that with transform it does not give any error?
Because you get lucky and the local VTK pipleine update happening under the hood works, it is not officially supported though.
> would be awsome if when fetch is called updatePipeline is called also, as it is a necessary thing
Possible to add, please open an issue.