model_config.md

Behaviour of pydantic can be controlled via the Config class on a model or a pydantic dataclass.

{!.tmp_examples/model_config_main.md!}

Also, you can specify config options as model class kwargs: {!.tmp_examples/model_config_class_kwargs.md!}

Similarly, if using the @dataclass decorator: {!.tmp_examples/model_config_dataclass.md!}

Options

title : the title for the generated JSON Schema

anystr_strip_whitespace : whether to strip leading and trailing whitespace for str & byte types (default: False)

anystr_upper : whether to make all characters uppercase for str & byte types (default: False)

anystr_lower : whether to make all characters lowercase for str & byte types (default: False)

min_anystr_length : the min length for str & byte types (default: 0)

max_anystr_length : the max length for str & byte types (default: None)

validate_all : whether to validate field defaults (default: False)

extra : whether to ignore, allow, or forbid extra attributes during model initialization. Accepts the string values of 'ignore', 'allow', or 'forbid', or values of the Extra enum (default: Extra.ignore). 'forbid' will cause validation to fail if extra attributes are included, 'ignore' will silently ignore any extra attributes, and 'allow' will assign the attributes to the model.

allow_mutation : whether or not models are faux-immutable, i.e. whether __setattr__ is allowed (default: True)

frozen

!!! warning This parameter is in beta

: setting frozen=True does everything that allow_mutation=False does, and also generates a __hash__() method for the model. This makes instances of the model potentially hashable if all the attributes are hashable. (default: False)

use_enum_values : whether to populate models with the value property of enums, rather than the raw enum. This may be useful if you want to serialise model.dict() later (default: False)

fields : a dict containing schema information for each field; this is equivalent to using the Field class, except when a field is already defined through annotation or the Field class, in which case only alias, include, exclude, min_length, max_length, regex, gt, lt, gt, le, multiple_of, max_digits, decimal_places, min_items, max_items, unique_items and allow_mutation can be set (for example you cannot set default of default_factory) (default: None)

validate_assignment : whether to perform validation on assignment to attributes (default: False)

allow_population_by_field_name : whether an aliased field may be populated by its name as given by the model attribute, as well as the alias (default: False)

!!! note The name of this configuration setting was changed in v1.0 from allow_population_by_alias to allow_population_by_field_name.

error_msg_templates : a dict used to override the default error message templates. Pass in a dictionary with keys matching the error messages you want to override (default: {})

arbitrary_types_allowed : whether to allow arbitrary user types for fields (they are validated simply by checking if the value is an instance of the type). If False, RuntimeError will be raised on model declaration (default: False). See an example in Field Types.

orm_mode : whether to allow usage of ORM mode

getter_dict : a custom class (which should inherit from GetterDict) to use when decomposing arbitrary classes for validation, for use with orm_mode; see Data binding.

alias_generator : a callable that takes a field name and returns an alias for it; see the dedicated section

keep_untouched : a tuple of types (e.g. descriptors) for a model's default values that should not be changed during model creation and will not be included in the model schemas. Note: this means that attributes on the model with defaults of this type, not annotations of this type, will be left alone.

schema_extra : a dict used to extend/update the generated JSON Schema, or a callable to post-process it; see schema customization

json_loads : a custom function for decoding JSON; see custom JSON (de)serialisation

json_dumps : a custom function for encoding JSON; see custom JSON (de)serialisation

json_encoders : a dict used to customise the way types are encoded to JSON; see JSON Serialisation

underscore_attrs_are_private : whether to treat any underscore non-class var attrs as private, or leave them as is; see Private model attributes

copy_on_model_validation : string literal to control how models instances are processed during validation, with the following means (see #4093 for a full discussion of the changes to this field):

• 'none' - models are not copied on validation, they're simply kept "untouched"
• 'shallow' - models are shallow copied, this is the default
• 'deep' - models are deep copied

smart_union : whether pydantic should try to check all types inside Union to prevent undesired coercion; see the dedicated section

post_init_call : whether stdlib dataclasses __post_init__ should be run before (default behaviour with value 'before_validation') or after (value 'after_validation') parsing and validation when they are converted.

allow_inf_nan : whether to allow infinity (+inf an -inf) and NaN values to float fields, defaults to True, set to False for compatibility with JSON, see #3994 for more details, added in V1.10

Change behaviour globally

If you wish to change the behaviour of pydantic globally, you can create your own custom BaseModel with custom Config since the config is inherited {!.tmp_examples/model_config_change_globally_custom.md!}

Alias Generator

If data source field names do not match your code style (e. g. CamelCase fields), you can automatically generate aliases using alias_generator:

{!.tmp_examples/model_config_alias_generator.md!}

Here camel case refers to "upper camel case" aka pascal case e.g. CamelCase. If you'd like instead to use lower camel case e.g. camelCase, instead use the to_lower_camel function.

Alias Precedence

!!! warning Alias priority logic changed in v1.4 to resolve buggy and unexpected behaviour in previous versions. In some circumstances this may represent a breaking change, see #1178 and the precedence order below for details.

In the case where a field's alias may be defined in multiple places, the selected value is determined as follows (in descending order of priority):

1. Set via Field(..., alias=<alias>), directly on the model
2. Defined in Config.fields, directly on the model
3. Set via Field(..., alias=<alias>), on a parent model
4. Defined in Config.fields, on a parent model
5. Generated by alias_generator, regardless of whether it's on the model or a parent

!!! note This means an alias_generator defined on a child model does not take priority over an alias defined on a field in a parent model.

For example:

{!.tmp_examples/model_config_alias_precedence.md!}

Smart Union

By default, as explained here, pydantic tries to validate (and coerce if it can) in the order of the Union. So sometimes you may have unexpected coerced data.

{!.tmp_examples/model_config_smart_union_off.md!}

To prevent this, you can enable Config.smart_union. Pydantic will then check all allowed types before even trying to coerce. Know that this is of course slower, especially if your Union is quite big.

{!.tmp_examples/model_config_smart_union_on.md!}

!!! warning Note that this option does not support compound types yet (e.g. differentiate List[int] and List[str]). This option will be improved further once a strict mode is added in pydantic and will probably be the default behaviour in v2!

{!.tmp_examples/model_config_smart_union_on_edge_case.md!}