# Issue with MED to XDMF Conversion in FESTIM Workshop 8 **URL:** \ **Category:** User Support\ **Created:** [July 9, 2025, 10:33am UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125 "2025-07-09T10:33:47Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Andrea](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@Andrea](https://festim.discourse.group/u/Andrea)\ **Post date:** [July 9, 2025, 10:33am UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/1 "2025-07-09T10:33:47Z")
Hello, I’m learing how to use FESTIM and currently working on Workshop 8. I downloaded the `mesh.med` file from GitHub, but when I run the script, it doesn’t work. Here’s the code I’m using: ``` Import meshio def convert_med_to_xdmf( med_file, cell_file="mesh_domains.xdmf", facet_file="mesh_boundaries.xdmf", cell_type="tetra", facet_type="triangle", ): """Converts a MED mesh to XDMF Args: med_file (str): the name of the MED file cell_file (str, optional): the name of the file containing the volume markers. Defaults to "mesh_domains.xdmf". facet_file (str, optional): the name of the file containing the surface markers.. Defaults to "mesh_boundaries.xdmf". cell_type (str, optional): The topology of the cells. Defaults to "tetra". facet_type (str, optional): The topology of the facets. Defaults to "triangle". Returns: dict, dict: the correspondance dict, the cell types """ msh = meshio.read(med_file) correspondance_dict = msh.cell_tags cell_data_types = msh.cell_data_dict["cell_tags"].keys() for mesh_block in msh.cells: if mesh_block.type == cell_type: meshio.write_points_cells( cell_file, msh.points, [mesh_block], cell_data={"f": [-1 * msh.cell_data_dict["cell_tags"][cell_type]]}, ) elif mesh_block.type == facet_type: meshio.write_points_cells( facet_file, msh.points, [mesh_block], cell_data={"f": [-1 * msh.cell_data_dict["cell_tags"][facet_type]]}, ) return correspondance_dict, cell_data_types correspondance_dict, cell_data_types = convert_med_to_xdmf("mesh.med", cell_file="mesh_domains.xdmf", facet_file="mesh_boundaries.xdmf") print(correspondance_dict) ``` However, I get the following error: ``` File "/home/ndrea_i_aio/festim/CAD integration.py", line 47, in correspondance_dict, cell_data_types = convert_med_to_xdmf("mesh.med", cell_file="mesh_domains.xdmf", facet_file="mesh_boundaries.xdmf") File "/home/ndrea_i_aio/festim/CAD integration.py", line 27, in convert_med_to_xdmf cell_data_types = msh.cell_data_dict["cell_tags"].keys() KeyError: 'cell_tags' ``` How can I solve this issue? Thank you in advance! ---
**Author:** ![VVKulagin](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/vvkulagin/32/51_2.png) [@VVKulagin](https://festim.discourse.group/u/VVKulagin)\ **Post date:** [July 9, 2025, 11:14am UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/2 "2025-07-09T11:14:57Z")
Hi @Andrea! I could not reproduce your issue neither via pulling the Jupyter book from git, nor via making a standalone script. Would you mind checking the downloaded med-file (or sharing it here) and the installed dependencies (e.g. environment the installation procedure of which is described on the Workshop main page)? The task also works fine in [Binder](https://mybinder.org/v2/gh/festim-dev/FESTIM-workshop/main) ---
**Author:** ![Andrea](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@Andrea](https://festim.discourse.group/u/Andrea)\ **Post date:** [July 10, 2025, 10:23am UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/3 "2025-07-10T10:23:51Z")
Thank you for your prompt reply! I’m linking the downloaded `.med` file below. I installed `meshio` using Conda, following the instruction provided on [https://github.com/nschloe/meshio](https://github.com/nschloe/meshio), and I verified that all dependencies are installed correctly. I hope this answers all your questions—please let me know if you need anything else. [mesh.zip](https://festim.discourse.group/uploads/short-url/zI9K9ZczpbCpTf6w5bripaKC9NN.zip) (1.8 MB) ---
**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\ **Post date:** [July 10, 2025, 1:34pm UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/4 "2025-07-10T13:34:22Z")
@Andrea what cells do you have in your mesh? tetrahedra? triangles? By default, `cell_type` defaults to `"tetra"` and `facet_type` defaults to `"triangle"`. For exampe, if you have a 2D mesh with triangles for cells then you need ```python convert_med_to_xdmf( med_file, cell_file="mesh_domains.xdmf", facet_file="mesh_boundaries.xdmf", cell_type="triangle", facet_type="line", ) ``` ---
**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\ **Post date:** [July 10, 2025, 1:43pm UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/5 "2025-07-10T13:43:13Z")
Also, what version of `meshio` are you using? ---
**Author:** ![Andrea](https://avatars.discourse-cdn.com/v4/letter/a/c37758/32.png) [@Andrea](https://festim.discourse.group/u/Andrea)\ **Post date:** [July 10, 2025, 3:33pm UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/6 "2025-07-10T15:33:26Z")
Thank you very much for your help. I’m using version 5.3.5 of `meshio`. I replaced the `mesh.med` file from [GitHub](https://github.com/festim-dev/FESTIM-workshop/tree/main/book/content/task08) with the one used in the [Binder](https://hub.gesis.mybinder.org/user/festim-dev-festim-workshop-d4luzq1u/lab/tree/book/content/task08.ipynb) environment, and now everything works correctly. Thanks again for the support! ---
**Author:** ![remidm](https://yyz2.discourse-cdn.com/free1/user_avatar/festim.discourse.group/remidm/32/4_2.png) [@remidm](https://festim.discourse.group/u/remidm)\ **Post date:** [July 10, 2025, 3:48pm UTC](https://festim.discourse.group/t/issue-with-med-to-xdmf-conversion-in-festim-workshop-8/125/7 "2025-07-10T15:48:00Z")
@Andrea glad that things are now working! The files in Github and Binder are the exact same files (because Binder is nothing more than a copy of the github repository with the installed dependencies). The issue was somewhere else probably. 😃