# Loading multiple files for a custom Python reader
**URL:** https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452
**Category:** Development
**Created:** [November 22, 2021, 3:40pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452 "2021-11-22T15:40:56Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@David\_Cortes](https://discourse.paraview.org/u/David_Cortes)
#### Post date: [November 22, 2021, 3:40pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/1 "2021-11-22T15:40:56Z")
Hi, I’m writing a reader in Python based on this documentation [util.vtkAlgorithm Module — ParaView/Python 5.9.1 documentation](https://kitware.github.io/paraview-docs/latest/python/paraview.util.vtkAlgorithm.html) How can I load multiple files and assign them a `timestep` as Paraview does automatically when loading multiple VTK files with a similar filename such as `0000`, `0001`, etc.?
When I load multiple files using a wildcard, say `*.ovf` , Paraview only reads the first file from the list. In the documentation, time steps are implemented but this is only done by reading the input’s file time column. In my case I need to assign a “time” based on the filenames. I also found this [https://www.paraview.org/Wiki/Animating\_legacy\_VTK\_file\_series](https://www.paraview.org/Wiki/Animating_legacy_VTK_file_series) but I’m not sure how to implement that using the `@smproperty` decorators .
Is there a way to obtain/access the list of files loaded by Paraview when selecting multiple files so to assign them a time step?
Also, is `vtkFileSeriesReader` involved when reading multiple files with similar names?
---
### Author:  [@theodorebaltis](https://discourse.paraview.org/u/theodorebaltis)
#### Post date: [November 22, 2021, 5:34pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/2 "2021-11-22T17:34:26Z")
I’m no expert but I believe that in general readers that accept multiple files actually read them in as an explicit list. The wildcard/family selection mechanism is only implemented in the file dialog, but the wildcard is expanded to an explicit list before being passed to the reader.
For example, the XDMFReader Python signature is
```python
reader = XDMFReader(registrationName='name', FileNames=['/path/to/file_001.xmf2', '/path/to/file_002.xmf2', '/path/to/file_003.xmf2'])
```
The XDMF format has a way to define time for each file. If a format does not (or if the times are not defined) then I think each file is given an arbitrary time of 1s,2s,3s, etc. If a format does not support time, then you can create a wrapper meta-file where you define times for each file.
Check out [https://discourse.paraview.org/t/assign-time-to-a-timestep/3505](https://discourse.paraview.org/t/assign-time-to-a-timestep/3505)
And yes I believe that in general readers are written for an individual file, and the `vtkFileSeriesReader` is used as a manager to hold all the file names and pass them to the reader as requested.
---
### Author:  [@David\_Cortes](https://discourse.paraview.org/u/David_Cortes)
#### Post date: [November 24, 2021, 7:35pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/3 "2021-11-24T19:35:07Z")
> [@theodorebaltis](#):
>
> ```auto
>
> ```
Thank you, but I thought there was a Python way to register the filenames using the decorators. I think I can try to do something with the XML strings
---
### Author:  [@theodorebaltis](https://discourse.paraview.org/u/theodorebaltis)
#### Post date: [November 29, 2021, 4:35pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/4 "2021-11-29T16:35:51Z")
Sorry I misunderstood.
From a Python-based reader I wrote, here is the method used to ingest files.
Note that I’m using the `vtkXdmfReader` internally.
```python
@smproperty.stringvector(name="FileNames",
label="File Names",
animateable="1",
clean_command="RemoveAllFileNames",
command="AddFileName",
repeat_command="1",
number_of_elements="1",
panel_visibility="never"
)
@smdomain.filelist()
@smhint.filechooser(extensions="xmf", file_description="Velodyne Lagrangian XMF files")
def AddFileName(self, name):
if name == 'None':
return
_ndata = vtkXdmfReader()
_ndata.CanReadFile(name)
_ndata.SetFileName(name)
_ndata.UpdateInformation()
#-- Timestep stuff
#- Get timesteps
executive = self.GetExecutive()
timesteps = _ndata.GetOutputInformation(0).Get(executive.TIME_STEPS())
#- Add timestep(s) to internal tracking
self._timesteps.extend(timesteps)
self._timesteps = sorted(self._timesteps)
```
This method will run on all files passed from the file browser dialog.
Later on I use the collected time information like so:
```python
def RequestInformation(self, request, inInfoVec, outInfoVec):
executive = self.GetExecutive()
outInfo = outInfoVec.GetInformationObject(0)
outInfo.Remove(executive.TIME_STEPS())
outInfo.Remove(executive.TIME_RANGE())
timesteps = self._timesteps
if timesteps != []:
for t in timesteps:
outInfo.Append(executive.TIME_STEPS(), t)
outInfo.Append(executive.TIME_RANGE(), timesteps[0])
outInfo.Append(executive.TIME_RANGE(), timesteps[-1])
```
Check out this link:
[https://public.kitware.com/pipermail/paraview/2013-September/029316.html](https://public.kitware.com/pipermail/paraview/2013-September/029316.html)
---
### Author:  [@David\_Cortes](https://discourse.paraview.org/u/David_Cortes)
#### Post date: [November 30, 2021, 1:58pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/5 "2021-11-30T13:58:50Z")
Thanks, this is very helpful. Do you know where exactly the data changes when updating the time step in Paraview? Is this done in the RequestData method?
---
### Author:  [@theodorebaltis](https://discourse.paraview.org/u/theodorebaltis)
#### Post date: [November 30, 2021, 3:03pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/6 "2021-11-30T15:03:01Z")
Yup, in `RequestData`.
The “util.vtkAlgorithm Module” link you originally posted has a few good examples of how to implement `RequestData`.
I personally followed the PythonCSVReader example pretty closely for updating the timestep and pulling the raw data, except I used an internal dictionary to map timesteps to the associated files (I appended the mappings in the `AddFileName` method, which is not part of the PythonCSVReader example, and also not shown in the posted code above - I clipped out some of the more complicated/usage-specific stuff).
---
### Author:  [@David\_Cortes](https://discourse.paraview.org/u/David_Cortes)
#### Post date: [November 30, 2021, 3:13pm UTC](https://discourse.paraview.org/t/loading-multiple-files-for-a-custom-python-reader/8452/7 "2021-11-30T15:13:36Z")
I see, I ended up doing the same, although it’s a bit hard to map time step floating numbers in a dictionary or list, so for now I’m only using integers. Do you know if there is a way to get the time step index directly from Paraview’s interface?
Thanks so much for the help 🙂