MCP Versions 0.3.0 and higher are incompatible with Pydantic V2

[gmichelhelcim]

Just some days ago, spinning up the MCP server with

uvx mcp-server-datahub@latest

worked without issues.

When spinning it up today, the server crashes with the following error, before it can run startup client tests.

 π sentinel 466-phishing-alert-refinements ✗ ❯ uvx mcp-server-datahub@0.3.0
Installed 85 packages in 111ms
/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/_internal/_config.py:383: UserWarning: Valid config keys have changed in V2:
* 'allow_population_by_field_name' has been renamed to 'validate_by_name'
  warnings.warn(message, UserWarning)
Traceback (most recent call last):
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/bin/mcp-server-datahub", line 6, in <module>
    from mcp_server_datahub.__main__ import main
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/mcp_server_datahub/__main__.py", line 11, in <module>
    from fastmcp.server.middleware import CallNext, Middleware, MiddlewareContext
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/fastmcp/__init__.py", line 5, in <module>
    from fastmcp.settings import Settings
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/fastmcp/settings.py", line 58, in <module>
    class Settings(BaseSettings):
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/_internal/_model_construction.py", line 242, in __new__
    set_model_fields(cls, config_wrapper=config_wrapper, ns_resolver=ns_resolver)
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/_internal/_model_construction.py", line 566, in set_model_fields
    fields, class_vars = collect_model_fields(cls, config_wrapper, ns_resolver, typevars_map=typevars_map)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/_internal/_fields.py", line 364, in collect_model_fields
    field_info = FieldInfo_.from_annotated_attribute(ann_type, assigned_value, _source=AnnotationSource.CLASS)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/fields.py", line 443, in from_annotated_attribute
    field_info = FieldInfo._construct(
                 ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/fields.py", line 519, in _construct
    merged_field_info = cls(**merged_kwargs)
                        ^^^^^^^^^^^^^^^^^^^^
  File "/Users/gmichel/.cache/uv/archive-v0/lobeYhps_c8WwK7J6L20H/lib/python3.12/site-packages/pydantic/fields.py", line 232, in __init__
    raise TypeError('cannot specify both default and default_factory')
TypeError: cannot specify both default and default_factory

uv/uvx version: uv 0.8.0 (0b2357294 2025-07-17)
python3 --version: Python 3.13.3

[nick93201]

anyone help resolving this issue ?

[gmichelhelcim]

Fixed in #50