See Changelog.

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Highlights

• add python 3.10 support, #2885 by @PrettyWood
• Discriminated unions, #619 by @PrettyWood
• Config.smart_union for better union logic, #2092 by @PrettyWood
• Binaries for Macos M1 CPUs, #3498 by @samuelcolvin
• Complex types can be set via nested environment variables, e.g. foo___bar, #3159 by @Air-Mark
• add a dark mode to pydantic documentation, #2913 by @gbdlin
• Add support for autocomplete in VS Code via __dataclass_transform__, #2721 by @tiangolo

Changes

• Add support for Decimal-specific validation configurations in Field(), additionally to using condecimal(), to allow better support from editors and tooling, #3507 by @tiangolo
• Add arm64 binaries suitable for MacOS with an M1 CPU to PyPI, #3498 by @samuelcolvin
• Fix issue where None was considered invalid when using a Union type containing Any or object, #3444 by @tharradine
• When generating field schema, pass optional field argument (of type pydantic.fields.ModelField) to __modify_schema__() if present, #3434 by @jasujm
• Fix issue when pydantic fail to parse typing.ClassVar string type annotation, #3401 by @uriyyo
• Mention Python >= 3.9.2 as an alternative to typing_extensions.TypedDict, #3374 by @BvB93
• Changed the validator method name in the Custom Errors example to more accurately describe what the validator is doing; changed from name_must_contain_space to value_must_equal_bar, #3327 by @michaelrios28
• Add AmqpDsn class, #3254 by @kludex
• Always use Enum value as default in generated JSON schema, #3190 by @joaommartins
• Add support for Mypy 0.920, #3175 by @christianbundy
• validate_arguments now supports extra customization (used to always be Extra.forbid), #3161 by @PrettyWood
• Complex types can be set by nested environment variables, #3159 by @Air-Mark
• Fix mypy plugin to collect fields based on pydantic.utils.is_valid_field so that it ignores untyped private variables, #3146 by @hi-ogawa
• fix validate_arguments issue with Config.validate_all, #3135 by @PrettyWood
• avoid dict coercion when using dict subclasses as field type, #3122 by @PrettyWood
• add support for object type, #3062 by @PrettyWood
• Updates pydantic dataclasses to keep _special properties on parent classes, #3043 by @zulrang
• Add a TypedDict class for error objects, #3038 by @matthewhughes934
• Fix support for using a subclass of an annotation as a default, #3018 by @JacobHayes
• make create_model_from_typeddict mypy compliant, #3008 by @PrettyWood
• Make multiple inheritance work when using PrivateAttr, #2989 by @hmvp
• Parse environment variables as JSON, if they have a Union type with a complex subfield, #2936 by @cbartz
• Prevent StrictStr permitting Enum values where the enum inherits from str, #2929 by @samuelcolvin
• Make SecretsSettingsSource parse values being assigned to fields of complex types when sourced from a secrets file, just as when sourced from environment variables, #2917 by @davidmreed
• add a dark mode to pydantic documentation, #2913 by @gbdlin
• Make pydantic-mypy plugin compatible with pyproject.toml configuration, consistent with mypy changes. See the doc for more information, #2908 by @jrwalk
• add python 3.10 support, #2885 by @PrettyWood
• Correctly parse generic models with Json[T], #2860 by @geekingfrog
• Update contrib docs re: python version to use for building docs, #2856 by @paxcodes
• Clarify documentation about pydantic's support for custom validation and strict type checking, despite pydantic being primarily a parsing library, #2855 by @paxcodes
• Fix schema generation for Deque fields, #2810 by @sergejkozin
• fix an edge case when mixing constraints and Literal, #2794 by @PrettyWood
• Fix postponed annotation resolution for NamedTuple and TypedDict when they're used directly as the type of fields within Pydantic models, #2760 by @jameysharp
• Fix bug when mypy plugin fails on construct method call for BaseSettings derived classes, #2753 by @uriyyo
• Add function overloading for a pydantic.create_model function, #2748 by @uriyyo
• Fix mypy plugin issue with self field declaration, #2743 by @uriyyo
• The colon at the end of the line "The fields which were supplied when user was initialised:" suggests that the code following it is related. Changed it to a period, #2733 by @krisaoe
• Renamed variable schema to schema_ to avoid shadowing of global variable name, #2724 by @shahriyarr
• Add support for autocomplete in VS Code via __dataclass_transform__, #2721 by @tiangolo
• add missing type annotations in BaseConfig and handle max_length = 0, #2719 by @PrettyWood
• Change orm_mode checking to allow recursive ORM mode parsing with dicts, #2718 by @nuno-andre
• Add episode 313 of the Talk Python To Me podcast, where Michael Kennedy and Samuel Colvin discuss pydantic, to the docs, #2712 by @RatulMaharaj
• fix JSON schema generation when a field is of type NamedTuple and has a default value, #2707 by @PrettyWood
• Enum fields now properly support extra kwargs in schema generation, #2697 by @sammchardy
• Make serialization of referenced pydantic models possible, #2650 by @PrettyWood
• Add uniqueItems option to ConstrainedList, #2618 by @nuno-andre
• Try to evaluate forward refs automatically at model creation, #2588 by @uriyyo
• Switch docs preview and coverage display to use smokeshow, #2580 by @samuelcolvin
• Add __version__ attribute to pydantic module, #2572 by @paxcodes
• Add postgresql+asyncpg, postgresql+pg8000, postgresql+psycopg2, postgresql+psycopg2cffi, postgresql+py-postgresql and postgresql+pygresql schemes for PostgresDsn, #2567 by @postgres-asyncpg
• Enable the Hypothesis plugin to generate a constrained decimal when the decimal_places argument is specified, #2524 by @cwe5590
• Allow collections.abc.Callable to be used as type in python 3.9, #2519 by @daviskirk
• Documentation update how to custom compile pydantic when using pip install, small change in setup.py to allow for custom CFLAGS when compiling, #2517 by @peterroelants
• remove side effect of default_factory to run it only once even if Config.validate_all is set, #2515 by @PrettyWood
• Add lookahead to ip regexes for AnyUrl hosts. This allows urls with DNS labels looking like IPs to validate as they are perfectly valid host names, #2512 by @sbv-csis
• Set minItems and maxItems in generated JSON schema for fixed-length tuples, #2497 by @PrettyWood
• Add strict argument to conbytes, #2489 by @koxudaxi
• Support user defined generic field types in generic models, #2465 by @daviskirk
• Add an example and a short explanation of subclassing GetterDict to docs, #2463 by @nuno-andre
• add KafkaDsn type, HttpUrl now has default port 80 for http and 443 for https, #2447 by @MihanixA
• Add PastDate and FutureDate types, #2425 by @Kludex
• Support generating schema for Generic fields with subtypes, #2375 by @maximberg
• fix(encoder): serialize NameEmail to str, #2341 by @alecgerona
• add Config.smart_union to prevent coercion in Union if possible, see the doc for more information, #2092 by @PrettyWood
• Add ability to use typing.Counter as a model field type, #2060 by @uriyyo
• Add parameterised subclasses to __bases__ when constructing new parameterised classes, so that A <: B => A[int] <: B[int], #2007 by @diabolo-dan
• Create FileUrl type that allows URLs that conform to RFC 8089. Add host_required parameter, which is True by default (AnyUrl and subclasses), False in RedisDsn, FileUrl, #1983 by @vgerak
• add confrozenset(), analogous to conset() and conlist(), #1897 by @PrettyWood
• stop calling parent class root_validator if overridden, #1895 by @PrettyWood
• Add repr (defaults to True) parameter to Field, to hide it from the default representation of the BaseModel, #1831 by @fnep
• Accept empty query/fragment URL parts, #1807 by @xavier
• Add "exclude" as a field parameter so that it can be configured using model config instead of purely at .dict / .json export time, #660 by @daviskirk

Full List of changes: https://github.com/samuelcolvin/pydantic/compare/v1.8.2...v1.9.0a1