# MedCAT Trainer -- cannot export JSON CUI filter

**URL:** <https://discourse.cogstack.org/t/medcat-trainer-cannot-export-json-cui-filter/382>\
**Category:** MedCAT\
**Created:** [May 9, 2026, 12:57pm UTC](https://discourse.cogstack.org/t/medcat-trainer-cannot-export-json-cui-filter/382 "2026-05-09T12:57:27Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![ollielloyd](https://avatars.discourse-cdn.com/v4/letter/o/71c47a/32.png) [@ollielloyd](https://discourse.cogstack.org/u/ollielloyd)\
**Post date:** [May 9, 2026, 12:57pm UTC](https://discourse.cogstack.org/t/medcat-trainer-cannot-export-json-cui-filter/382/1 "2026-05-09T12:57:27Z")

</div>

When trying to download a concerpt filter JSON from the concepts tab I get this error:

```python
[medcattrainer] Internal Server Error: /api/generate-concept-filter-json/
[medcattrainer] Traceback (most recent call last):
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/core/handlers/exception.py", line 55, in inner
[medcattrainer] response = get_response(request)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/core/handlers/base.py", line 197, in _get_response
[medcattrainer] response = wrapped_callback(request, *callback_args, **callback_kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/views/decorators/csrf.py", line 65, in _view_wrapper
[medcattrainer] return view_func(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/views/generic/base.py", line 105, in view
[medcattrainer] return self.dispatch(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 515, in dispatch
[medcattrainer] response = self.handle_exception(exc)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 475, in handle_exception
[medcattrainer] self.raise_uncaught_exception(exc)
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 486, in raise_uncaught_exception
[medcattrainer] raise exc
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 512, in dispatch
[medcattrainer] response = handler(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/decorators.py", line 50, in handler
[medcattrainer] return func(*args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/api/api/views.py", line 1076, in generate_concept_filter_flat_json
[medcattrainer] filter_json = json.dumps(final_filter)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/ __init__.py", line 231, in dumps
[medcattrainer] return _default_encoder.encode(obj)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 200, in encode
[medcattrainer] chunks = self.iterencode(o, _one_shot=True)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 258, in iterencode
[medcattrainer] return _iterencode(o, 0)
[medcattrainer] ^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 180, in default
[medcattrainer] raise TypeError(f'Object of type {o. __class__. __name__ } '
[medcattrainer] TypeError: Object of type dict_keys is not JSON serializable
[medcattrainer] ERROR 2026-05-09 12:49:26,005 log.py l:253:Internal Server Error: /api/generate-concept-filter-json/
[medcattrainer] Traceback (most recent call last):
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/core/handlers/exception.py", line 55, in inner
[medcattrainer] response = get_response(request)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/core/handlers/base.py", line 197, in _get_response
[medcattrainer] response = wrapped_callback(request, *callback_args, **callback_kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/views/decorators/csrf.py", line 65, in _view_wrapper
[medcattrainer] return view_func(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/django/views/generic/base.py", line 105, in view
[medcattrainer] return self.dispatch(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 515, in dispatch
[medcattrainer] response = self.handle_exception(exc)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 475, in handle_exception
[medcattrainer] self.raise_uncaught_exception(exc)
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 486, in raise_uncaught_exception
[medcattrainer] raise exc
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/views.py", line 512, in dispatch
[medcattrainer] response = handler(request, *args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/.venv/lib/python3.12/site-packages/rest_framework/decorators.py", line 50, in handler
[medcattrainer] return func(*args, **kwargs)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/home/api/api/views.py", line 1076, in generate_concept_filter_flat_json
[medcattrainer] filter_json = json.dumps(final_filter)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/ __init__.py", line 231, in dumps
[medcattrainer] return _default_encoder.encode(obj)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 200, in encode
[medcattrainer] chunks = self.iterencode(o, _one_shot=True)
[medcattrainer] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 258, in iterencode
[medcattrainer] return _iterencode(o, 0)
[medcattrainer] ^^^^^^^^^^^^^^^^^
[medcattrainer] File "/usr/local/lib/python3.12/json/encoder.py", line 180, in default
[medcattrainer] raise TypeError(f'Object of type {o. __class__. __name__ } '
[medcattrainer] TypeError: Object of type dict_keys is not JSON serializable

```

**Root cause:** After deduplicating the concept list, `final_filter` ends up as a `dict_keys` object (not a plain list). `json.dumps()` can’t serialise `dict_keys`, so it crashes.

**File:** `webapp/api/api/views.py` line 1086

**Before:** filter\_json = json.dumps(final\_filter)

**Patch:** filter\_json = json.dumps(list(final\_filter))

Happy to help create pull request if helpful.

---

<div class="post-metadata">

**Author:** ![mart.ratas](https://avatars.discourse-cdn.com/v4/letter/m/e79b87/32.png) [@mart.ratas](https://discourse.cogstack.org/u/mart.ratas)\
**Post date:** [May 11, 2026, 8:36am UTC](https://discourse.cogstack.org/t/medcat-trainer-cannot-export-json-cui-filter/382/2 "2026-05-11T08:36:15Z")

</div>

Thanks for the feedback!

Yes, this does look like an issue ineed.

And the fix you’ve outlined seems decent as well. So if you don’t mind pushing that as a PR as well, we’d really appreciate it!