Pydantic v2 migration: 'PydanticDeprecatedSince20' warnings and errors for class Config, @validator, @root_validator, .dict(), .json(), parse_obj, from_orm and BaseSettings import error. What are the replacements?

Cause: Pydantic 2 reworked the API. Most v1 names still exist but emit deprecation warnings and will be removed in a later major version; some features were removed or moved to other packages, which produces errors. Typical symptoms after upgrading: DeprecationWarnings about class-based config, @validator and .dict(), an ImportError for BaseSettings from pydantic, or removed config keys being rejected or ignored. Fix (rename map from the official migration guide): 1. Config: replace the inner class Config with a model_config = ConfigDict(...) attribute (from pydantic import ConfigDict). Renamed keys include orm_mode -> from_attributes, allow_population_by_field_name -> populate_by_name, schema_extra -> json_schema_extra, validate_all -> validate_default, anystr_strip_whitespace -> str_strip_whitespace. allow_mutation is replaced by frozen (inverted meaning). 2. Validators: @validator -> @field_validator (each_item is gone, always=True becomes validate_default on the field); @root_validator -> @model_validator; @validate_arguments -> @validate_call. Field validators in v2 should be classmethods, so add @classmethod below the decorator. 3. Methods: .dict() -> .model_dump(); .json() -> .model_dump_json(); .copy() -> .model_copy(); parse_obj() -> model_validate(); parse_raw() -> model_validate_json(); construct() -> model_construct(); update_forward_refs() -> model_rebuild(); from_orm() -> model_validate() with from_attributes enabled; parse_obj_as -> TypeAdapter. 4. BaseSettings moved to a separate package: pip install pydantic-settings, then from pydantic_settings import BaseSettings. 5. For a large codebase, try the beta codemod: pip install bump-pydantic, run it on your package directory, review the diff, and run tests. If you depend on libraries that still need v1, either upgrade them or pin pydantic<2 for now. 6. Surface remaining warnings in tests with python -W error::DeprecationWarning -m pytest (or pytest -W error::DeprecationWarning) so none are missed. Verify: pip show pydantic reports 2.x, the test suite runs with no Pydantic deprecation warnings, and no import of BaseSettings from pydantic remains (grep the codebase). Sources: https://pydantic.dev/docs/validation/latest/get-started/migration/ https://pydantic.dev/docs/validation/latest/concepts/config/ https://pydantic.dev/docs/validation/latest/concepts/validators/