topic Re: Issue with pydantic in ArcGIS API for Python Questions

Issue with pydantic

HamzaMerini — Mon, 08 Jun 2026 11:56:59 GMT

Hi everyone,

I'm migrating from ArcGIS Pro 3.1 to 3.4 and updating my code from `arcgis.mapping.WebMap` to `arcgis.map.Map` accordingly.

**Environment:**
- ArcGIS Pro 3.4
- arcgis 2.4.0
- arcgis-mapping 4.30.0
- Python 3.11 (conda env)
- Windows 10

**The issue:**
When instantiating `Map(item=webmap_item)`, I get the following error:

```
TypeError: 'MockValSer' object is not an instance of 'SchemaSerializer'
File "...arcgis\map\map_widget.py", line 488, in _update_source
self._webmap_dict = self._webmap.dict()
File "...arcgis\map\_dataclasses\_webmap_spec.py", line 73, in dict
d = super().model_dump(
File "...pydantic\main.py", line 475, in model_dump
return self.__pydantic_serializer__.to_python(
```

This seems to be a conflict between `arcgis-mapping 4.30.0` and pydantic v2. I've tried multiple pydantic v2 versions (2.4.0, 2.5.0, 2.13.4) with their matching `pydantic-core` versions, reinstalling from both pip and conda-forge, but the error persists.

Has anyone successfully used `arcgis.map.Map` on Windows with ArcGIS Pro 3.4? If so, what exact version of pydantic are you running?

Thanks!

Re: Issue with pydantic

DanPatterson — Mon, 08 Jun 2026 15:01:26 GMT

2.4.2 according to the package release by version document

arcpy/docs/ArcGIS-Pro-Python-Distribution-By-Release.pdf at main · Esri/arcpy

Re: Issue with pydantic

HamzaMerini — Tue, 09 Jun 2026 13:17:32 GMT

I updated pydantic to 2.4.2 but still have an issue

Re: Issue with pydantic

DanPatterson — Tue, 09 Jun 2026 15:48:55 GMT

sounds like an issue with what you are using whatever MockValSer is.

Tech Support would be your best bet, especially since you have the correct version of pydantic installed for your version of Pro. Perhaps other issues have been seen that are addressed in more recent versions of Pro.

Good luck