Fields

Field classes for various types of data.

Classes

Field(*, default, missing, data_key, …)	Basic field from which other fields should extend.
Raw(*, default, missing, data_key, …)	Field that applies no formatting.
Nested(nested, type, str, Callable[[], …)	Allows you to nest a Schema inside a field.
Mapping(keys, type] = None, values, …)	An abstract class for objects with key-value pairs.
Dict(keys, type] = None, values, …)	A dict field.
List(cls_or_instance, type], **kwargs)	A list field, composed with another Field class or instance.
Tuple(tuple_fields, *args, **kwargs)	A tuple field, composed of a fixed number of other Field classes or
String(*, default, missing, data_key, …)	A string field.
UUID(*, default, missing, data_key, …)	A UUID field.
Number(*, as_string, **kwargs)	Base class for number fields.
Integer(*, strict, **kwargs)	An integer field.
Decimal(places, rounding, *, allow_nan, …)	A field that (de)serializes to the Python decimal.Decimal type.
Boolean(*, truthy, falsy, **kwargs)	A boolean field.
Float(*, allow_nan, as_string, **kwargs)	A double as an IEEE-754 double precision string.
DateTime(format, **kwargs)	A formatted datetime string.
NaiveDateTime(format, *, timezone, **kwargs)	A formatted naive datetime string.
AwareDateTime(format, *, default_timezone, …)	A formatted aware datetime string.
Time(*, default, missing, data_key, …)	ISO8601-formatted time string.
Date(format, **kwargs)	ISO8601-formatted date string.
TimeDelta(precision, **kwargs)	A field that (de)serializes a datetime.timedelta object to an integer and vice versa.
Url(*, relative, schemes, Set[str]] = None, …)	A validated URL field.
URL	A validated URL field.
Email(*args, **kwargs)	A validated email field.
Method(serialize, deserialize, **kwargs)	A field that takes the value returned by a Schema method.
Function(serialize, Any], Callable[[Any, …)	A field that takes the value returned by a function.
Str	A string field.
Bool	A boolean field.
Int	An integer field.
Constant(constant, **kwargs)	A field that (de)serializes to a preset constant.
Pluck(nested, type, str, Callable[[], …)	Allows you to replace nested data with one of the data’s fields.

class marshmallow.fields.AwareDateTime(format: str = None, *, default_timezone: datetime.timezone = None, **kwargs)

A formatted aware datetime string.

Parameters

• format – See DateTime.

• default_timezone – Used on deserialization. If None, naive datetimes are rejected. If not None, naive datetimes are set this timezone.

• kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)

Deserialize value.

New in version 3.0.0rc9.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

marshmallow.fields.Bool

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Methods

alias of marshmallow.fields.Boolean

class marshmallow.fields.Boolean(*, truthy: Set = None, falsy: Set = None, **kwargs)

A boolean field.

Parameters

• truthy – Values that will (de)serialize to True. If an empty set, any non-falsy value will deserialize to True. If None, marshmallow.fields.Boolean.truthy will be used.

• falsy – Values that will (de)serialize to False. If None, marshmallow.fields.Boolean.falsy will be used.

• kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages	Default error messages.
falsy	Default falsy values.
truthy	Default truthy values.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'invalid': 'Not a valid boolean.'}

Default error messages.

falsy = {'NO', 0, 'n', 'False', 'F', 'FALSE', 'off', 'No', 'Off', '0', 'N', 'false', 'f', 'no', 'OFF'}

Default falsy values.

truthy = {'YES', 'on', 1, 'Y', 't', 'ON', 'On', '1', 'T', 'true', 'TRUE', 'y', 'Yes', 'yes', 'True'}

Default truthy values.

class marshmallow.fields.Constant(constant: Any, **kwargs)

A field that (de)serializes to a preset constant. If you only want the constant added for serialization or deserialization, you should use dump_only=True or load_only=True respectively.

Parameters

constant – The constant to return for the field attribute.

Methods

_deserialize(value, *args, **kwargs)	Deserialize value.
_serialize(value, *args, **kwargs)	Serializes value to a basic Python datatype.

New in version 2.0.0.

_deserialize(value, *args, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, *args, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

class marshmallow.fields.Date(format: str = None, **kwargs)

ISO8601-formatted date string.

Parameters

• format – Either "iso" (for ISO8601) or a date format string. If None, defaults to “iso”.

• kwargs – The same keyword arguments that Field receives.

Attributes

default_error_messages

Default error messages.

default_error_messages = {'format': '"{input}" cannot be formatted as a date.', 'invalid': 'Not a valid date.'}

Default error messages.

class marshmallow.fields.DateTime(format: str = None, **kwargs)

A formatted datetime string.

Example: '2014-12-22T03:12:58.019077+00:00'

Parameters

• format – Either "rfc" (for RFC822), "iso" (for ISO8601), or a date format string. If None, defaults to “iso”.

• kwargs – The same keyword arguments that Field receives.

Methods

_bind_to_schema(field_name, schema)	Update field with values from its parent schema.
_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

Changed in version 3.0.0rc9: Does not modify timezone information on (de)serialization.

_bind_to_schema(field_name, schema)

Update field with values from its parent schema. Called by Schema._bind_field.

Parameters

• field_name (str) – Field name set in schema.

• schema (Schema) – Parent schema.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'format': '"{input}" cannot be formatted as a {obj_type}.', 'invalid': 'Not a valid {obj_type}.', 'invalid_awareness': 'Not a valid {awareness} {obj_type}.'}

Default error messages.

class marshmallow.fields.Decimal(places: int = None, rounding: str = None, *, allow_nan: bool = False, as_string: bool = False, **kwargs)

A field that (de)serializes to the Python decimal.Decimal type. It’s safe to use when dealing with money values, percentages, ratios or other numbers where precision is critical.

Warning

This field serializes to a decimal.Decimal object by default. If you need to render your data as JSON, keep in mind that the json module from the standard library does not encode decimal.Decimal. Therefore, you must use a JSON library that can handle decimals, such as simplejson, or serialize to a string by passing as_string=True.

Methods

_format_num(value)	Return the number value for value, given this field’s num_type.
_validated(value)	Format the value or raise a ValidationError if an error occurs.

Attributes

default_error_messages

Default error messages.

Classes

num_type

Construct a new Decimal object.

Warning

If a JSON float value is passed to this field for deserialization it will first be cast to its corresponding string value before being deserialized to a decimal.Decimal object. The default __str__ implementation of the built-in Python float type may apply a destructive transformation upon its input data and therefore cannot be relied upon to preserve precision. To avoid this, you can instead pass a JSON string to be deserialized directly.

Parameters

• places – How many decimal places to quantize the value. If None, does not quantize the value.

• rounding – How to round the value during quantize, for example decimal.ROUND_UP. If None, uses the rounding value from the current thread’s context.

• allow_nan – If True, NaN, Infinity and -Infinity are allowed, even though they are illegal according to the JSON specification.

• as_string – If True, serialize to a string instead of a Python decimal.Decimal type.

• kwargs – The same keyword arguments that Number receives.

New in version 1.2.0.

_format_num(value)

Return the number value for value, given this field’s num_type.

_validated(value)

Format the value or raise a ValidationError if an error occurs.

default_error_messages = {'special': 'Special numeric values (nan or infinity) are not permitted.'}

Default error messages.

num_type

alias of decimal.Decimal

class marshmallow.fields.Dict(keys: Union[marshmallow.fields.Field, type] = None, values: Union[marshmallow.fields.Field, type] = None, **kwargs)

A dict field. Supports dicts and dict-like objects. Extends Mapping with dict as the mapping_type.

Example:

numbers = fields.Dict(keys=fields.Str(), values=fields.Float())

Classes

mapping_type

dict() -> new empty dictionary

Parameters

kwargs – The same keyword arguments that Mapping receives.

New in version 2.1.0.

mapping_type

alias of builtins.dict

class marshmallow.fields.Email(*args, **kwargs)

A validated email field. Validation occurs during both serialization and deserialization.

Parameters

• args – The same positional arguments that String receives.

• kwargs – The same keyword arguments that String receives.

Attributes

default_error_messages

Default error messages.

default_error_messages = {'invalid': 'Not a valid email address.'}

Default error messages.

class marshmallow.fields.Field(*, default: Any = <marshmallow.missing>, missing: Any = <marshmallow.missing>, data_key: str = None, attribute: str = None, validate: Union[Callable[[Any], Any], Iterable[Callable[[Any], Any]]] = None, required: bool = False, allow_none: bool = None, load_only: bool = False, dump_only: bool = False, error_messages: Dict[str, str] = None, **metadata)

Basic field from which other fields should extend. It applies no formatting by default, and should only be used in cases where data does not need to be formatted before being serialized or deserialized. On error, the name of the field will be returned.

Parameters

• default – If set, this value will be used during serialization if the input value is missing. If not set, the field will be excluded from the serialized output if the input value is missing. May be a value or a callable.

• missing – Default deserialization value for the field if the field is not found in the input data. May be a value or a callable.

• data_key – The name of the dict key in the external representation, i.e. the input of load and the output of dump. If None, the key will match the name of the field.

• attribute – The name of the attribute to get the value from when serializing. If None, assumes the attribute has the same name as the field. Note: This should only be used for very specific use cases such as outputting multiple fields for a single attribute. In most cases, you should use data_key instead.

• validate – Validator or collection of validators that are called during deserialization. Validator takes a field’s input value as its only parameter and returns a boolean. If it returns False, an ValidationError is raised.

• required – Raise a ValidationError if the field value is not supplied during deserialization.

• allow_none – Set this to True if None should be considered a valid value during validation/deserialization. If missing=None and allow_none is unset, will default to True. Otherwise, the default is False.

• load_only – If True skip this field during serialization, otherwise its value will be present in the serialized data.

• dump_only – If True skip this field during deserialization, otherwise its value will be present in the deserialized object. In the context of an HTTP API, this effectively marks the field as “read-only”.

• error_messages (dict) – Overrides for Field.default_error_messages.

• metadata – Extra arguments to be stored as metadata.

Methods

_bind_to_schema(field_name, schema)	Update field with values from its parent schema.
_deserialize(value, attr, data, Any]], **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.
_validate(value)	Perform validation on value.
_validate_missing(value)	Validate missing values.
deserialize(value, attr, data, Any] = None, …)	Deserialize value.
fail(key, **kwargs)	Helper method that raises a ValidationError with an error message from self.error_messages.
get_value(obj, attr[, accessor, default])	Return the value for a given key from an object.
make_error(key, **kwargs)	Helper method to make a ValidationError with an error message from self.error_messages.
serialize(attr, obj, accessor, str, Any], …)	Pulls the value for the given key from the object, applies the field’s formatting and returns the result.

Attributes

context	The context dictionary for the parent Schema.
default_error_messages	Default error messages for various kinds of errors.
root	Reference to the Schema that this field belongs to even if it is buried in a container field (e.g.

Changed in version 2.0.0: Removed error parameter. Use error_messages instead.

Changed in version 2.0.0: Added allow_none parameter, which makes validation/deserialization of None consistent across fields.

Changed in version 2.0.0: Added load_only and dump_only parameters, which allow field skipping during the (de)serialization process.

Changed in version 2.0.0: Added missing parameter, which indicates the value for a field if the field is not found during deserialization.

Changed in version 2.0.0: default value is only used if explicitly set. Otherwise, missing values inputs are excluded from serialized output.

Changed in version 3.0.0b8: Add data_key parameter for the specifying the key in the input and output data. This parameter replaced both load_from and dump_to.

_bind_to_schema(field_name, schema)

Update field with values from its parent schema. Called by Schema._bind_field.

Parameters

• field_name (str) – Field name set in schema.

• schema (Schema) – Parent schema.

_deserialize(value: Any, attr: Optional[str], data: Optional[Mapping[str, Any]], **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value: Any, attr: str, obj: Any, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

_validate(value)

Perform validation on value. Raise a ValidationError if validation does not succeed.

_validate_missing(value)

Validate missing values. Raise a ValidationError if value should be considered missing.

property context

The context dictionary for the parent Schema.

default_error_messages = {'null': 'Field may not be null.', 'required': 'Missing data for required field.', 'validator_failed': 'Invalid value.'}

Default error messages for various kinds of errors. The keys in this dictionary are passed to Field.make_error. The values are error messages passed to marshmallow.exceptions.ValidationError.

deserialize(value: Any, attr: str = None, data: Mapping[str, Any] = None, **kwargs)

Deserialize value.

Parameters

• value – The value to deserialize.

• attr – The attribute/key in data to deserialize.

• data – The raw input data passed to Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – If an invalid value is passed or if a required value is missing.

fail(key: str, **kwargs)

Helper method that raises a ValidationError with an error message from self.error_messages.

Deprecated since version 3.0.0: Use make_error instead.

get_value(obj, attr, accessor=None, default=<marshmallow.missing>)

Return the value for a given key from an object.

Parameters

• obj (object) – The object to get the value from.

• attr (str) – The attribute/key in obj to get the value from.

• accessor (callable) – A callable used to retrieve the value of attr from the object obj. Defaults to marshmallow.utils.get_value.

make_error(key: str, **kwargs) → marshmallow.exceptions.ValidationError

Helper method to make a ValidationError with an error message from self.error_messages.

property root

Reference to the Schema that this field belongs to even if it is buried in a container field (e.g. List). Return None for unbound fields.

serialize(attr: str, obj: Any, accessor: Callable[[Any, str, Any], Any] = None, **kwargs)

Pulls the value for the given key from the object, applies the field’s formatting and returns the result.

Parameters

• attr – The attribute/key to get from the object.

• obj – The object to access the attribute/key from.

• accessor – Function used to access values from obj.

• kwargs – Field-specific keyword arguments.

class marshmallow.fields.Float(*, allow_nan: bool = False, as_string: bool = False, **kwargs)

A double as an IEEE-754 double precision string.

Parameters

• allow_nan (bool) – If True, NaN, Infinity and -Infinity are allowed, even though they are illegal according to the JSON specification.

• as_string (bool) – If True, format the value as a string.

• kwargs – The same keyword arguments that Number receives.

Methods

_validated(value)

Format the value or raise a ValidationError if an error occurs.

Attributes

default_error_messages

Default error messages.

Classes

num_type

Convert a string or number to a floating point number, if possible.

_validated(value)

Format the value or raise a ValidationError if an error occurs.

default_error_messages = {'special': 'Special numeric values (nan or infinity) are not permitted.'}

Default error messages.

num_type

alias of builtins.float

class marshmallow.fields.Function(serialize: Union[Callable[[Any], Any], Callable[[Any, Dict], Any]] = None, deserialize: Union[Callable[[Any], Any], Callable[[Any, Dict], Any]] = None, **kwargs)

A field that takes the value returned by a function.

Parameters

• serialize – A callable from which to retrieve the value. The function must take a single argument obj which is the object to be serialized. It can also optionally take a context argument, which is a dictionary of context variables passed to the serializer. If no callable is provided then the `load_only` flag will be set to True.

• deserialize – A callable from which to retrieve the value. The function must take a single argument value which is the value to be deserialized. It can also optionally take a context argument, which is a dictionary of context variables passed to the deserializer. If no callable is provided then `value` will be passed through unchanged.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Changed in version 2.3.0: Deprecated func parameter in favor of serialize.

Changed in version 3.0.0a1: Removed func parameter.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

marshmallow.fields.Int

num_type

int([x]) -> integer

Methods

_validated(value)

Format the value or raise a ValidationError if an error occurs.

Classes

alias of marshmallow.fields.Integer

class marshmallow.fields.Integer(*, strict: bool = False, **kwargs)

An integer field.

Parameters

• strict – If True, only integer types are valid. Otherwise, any value castable to int is valid.

• kwargs – The same keyword arguments that Number receives.

Methods

_validated(value)

Format the value or raise a ValidationError if an error occurs.

Attributes

default_error_messages

Default error messages.

Classes

num_type

int([x]) -> integer

_validated(value)

Format the value or raise a ValidationError if an error occurs.

default_error_messages = {'invalid': 'Not a valid integer.'}

Default error messages.

num_type

alias of builtins.int

class marshmallow.fields.List(cls_or_instance: Union[marshmallow.fields.Field, type], **kwargs)

A list field, composed with another Field class or instance.

Example:

numbers = fields.List(fields.Float())

Methods

_bind_to_schema(field_name, schema)	Update field with values from its parent schema.
_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

Parameters

• cls_or_instance – A field class or instance.

• kwargs – The same keyword arguments that Field receives.

Changed in version 2.0.0: The allow_none parameter now applies to deserialization and has the same semantics as the other fields.

Changed in version 3.0.0rc9: Does not serialize scalar values to single-item lists.

_bind_to_schema(field_name, schema)

Update field with values from its parent schema. Called by Schema._bind_field.

Parameters

• field_name (str) – Field name set in schema.

• schema (Schema) – Parent schema.

_deserialize(value, attr, data, **kwargs) → List[Any]

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs) → Optional[List[Any]]

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'invalid': 'Not a valid list.'}

Default error messages.

class marshmallow.fields.Mapping(keys: Union[marshmallow.fields.Field, type] = None, values: Union[marshmallow.fields.Field, type] = None, **kwargs)

An abstract class for objects with key-value pairs.

Parameters

• keys – A field class or instance for dict keys.

• values – A field class or instance for dict values.

• kwargs – The same keyword arguments that Field receives.

Methods

_bind_to_schema(field_name, schema)	Update field with values from its parent schema.
_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

Classes

mapping_type

dict() -> new empty dictionary

Note

When the structure of nested data is not known, you may omit the keys and values arguments to prevent content validation.

New in version 3.0.0rc4.

_bind_to_schema(field_name, schema)

Update field with values from its parent schema. Called by Schema._bind_field.

Parameters

• field_name (str) – Field name set in schema.

• schema (Schema) – Parent schema.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'invalid': 'Not a valid mapping type.'}

Default error messages.

mapping_type

alias of builtins.dict

class marshmallow.fields.Method(serialize: str = None, deserialize: str = None, **kwargs)

A field that takes the value returned by a Schema method.

Parameters

• serialize (str) – The name of the Schema method from which to retrieve the value. The method must take an argument obj (in addition to self) that is the object to be serialized.

• deserialize (str) – Optional name of the Schema method for deserializing a value The method must take a single argument value, which is the value to deserialize.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Changed in version 2.0.0: Removed optional context parameter on methods. Use self.context instead.

Changed in version 2.3.0: Deprecated method_name parameter in favor of serialize and allow serialize to not be passed at all.

Changed in version 3.0.0: Removed method_name parameter.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

class marshmallow.fields.NaiveDateTime(format: str = None, *, timezone: datetime.timezone = None, **kwargs)

A formatted naive datetime string.

Parameters

• format – See DateTime.

• timezone – Used on deserialization. If None, aware datetimes are rejected. If not None, aware datetimes are converted to this timezone before their timezone information is removed.

• kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)

Deserialize value.

New in version 3.0.0rc9.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

class marshmallow.fields.Nested(nested: Union[marshmallow.base.SchemaABC, type, str, Callable[[], marshmallow.base.SchemaABC]], *, default: Any = <marshmallow.missing>, only: Union[Sequence[str], Set[str]] = None, exclude: Union[Sequence[str], Set[str]] = (), many: bool = False, unknown: str = None, **kwargs)

Allows you to nest a Schema inside a field.

Examples:

class ChildSchema(Schema):
    id = fields.Str()
    name = fields.Str()
    # Use lambda functions when you need two-way nesting or self-nesting
    parent = fields.Nested(lambda: ParentSchema(only=("id",)), dump_only=True)
    siblings = fields.List(fields.Nested(lambda: ChildSchema(only=("id", "name"))))

class ParentSchema(Schema):
    id = fields.Str()
    children = fields.List(
        fields.Nested(ChildSchema(only=("id", "parent", "siblings")))
    )
    spouse = fields.Nested(lambda: ParentSchema(only=("id",)))

Methods

_deserialize(value, attr, data[, partial])	Same as Field._deserialize() with additional partial argument.
_serialize(nested_obj, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages	Default error messages.
schema	The nested Schema object.

When passing a Schema instance as the first argument, the instance’s exclude, only, and many attributes will be respected.

Therefore, when passing the exclude, only, or many arguments to fields.Nested, you should pass a Schema class (not an instance) as the first argument.

# Yes
author = fields.Nested(UserSchema, only=('id', 'name'))

# No
author = fields.Nested(UserSchema(), only=('id', 'name'))

Parameters

• nested – Schema instance, class, class name (string), or callable that returns a Schema instance.

• exclude – A list or tuple of fields to exclude.

• only – A list or tuple of fields to marshal. If None, all fields are marshalled. This parameter takes precedence over exclude.

• many – Whether the field is a collection of objects.

• unknown – Whether to exclude, include, or raise an error for unknown fields in the data. Use EXCLUDE, INCLUDE or RAISE.

• kwargs – The same keyword arguments that Field receives.

_deserialize(value, attr, data, partial=None, **kwargs)

Same as Field._deserialize() with additional partial argument.

Parameters

partial (bool|tuple) – For nested schemas, the partial parameter passed to Schema.load.

Changed in version 3.0.0: Add partial parameter.

_serialize(nested_obj, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'type': 'Invalid type.'}

Default error messages.

property schema

The nested Schema object.

Changed in version 1.0.0: Renamed from serializer to schema.

class marshmallow.fields.Number(*, as_string: bool = False, **kwargs)

Base class for number fields.

Parameters

• as_string (bool) – If True, format the serialized value as a string.

• kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_format_num(value)	Return the number value for value, given this field’s num_type.
_serialize(value, attr, obj, **kwargs)	Return a string if self.as_string=True, otherwise return this field’s num_type.
_validated(value)	Format the value or raise a ValidationError if an error occurs.

Attributes

default_error_messages

Default error messages.

Classes

num_type

Convert a string or number to a floating point number, if possible.

_deserialize(value, attr, data, **kwargs) → Optional[_T]

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_format_num(value) → Any

Return the number value for value, given this field’s num_type.

_serialize(value, attr, obj, **kwargs) → Optional[Union[str, _T]]

Return a string if self.as_string=True, otherwise return this field’s num_type.

_validated(value) → Optional[_T]

Format the value or raise a ValidationError if an error occurs.

default_error_messages = {'invalid': 'Not a valid number.', 'too_large': 'Number too large.'}

Default error messages.

num_type

alias of builtins.float

class marshmallow.fields.Pluck(nested: Union[marshmallow.base.SchemaABC, type, str, Callable[], marshmallow.base.SchemaABC]], field_name: str, **kwargs)

Allows you to replace nested data with one of the data’s fields.

Example:

from marshmallow import Schema, fields

class ArtistSchema(Schema):
    id = fields.Int()
    name = fields.Str()

class AlbumSchema(Schema):
    artist = fields.Pluck(ArtistSchema, 'id')


in_data = {'artist': 42}
loaded = AlbumSchema().load(in_data) # => {'artist': {'id': 42}}
dumped = AlbumSchema().dump(loaded)  # => {'artist': 42}

Methods

_deserialize(value, attr, data[, partial])	Same as Field._deserialize() with additional partial argument.
_serialize(nested_obj, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Parameters

• nested (Schema) – The Schema class or class name (string) to nest, or "self" to nest the Schema within itself.

• field_name (str) – The key to pluck a value from.

• kwargs – The same keyword arguments that Nested receives.

_deserialize(value, attr, data, partial=None, **kwargs)

Same as Field._deserialize() with additional partial argument.

Parameters

partial (bool|tuple) – For nested schemas, the partial parameter passed to Schema.load.

Changed in version 3.0.0: Add partial parameter.

_serialize(nested_obj, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

class marshmallow.fields.Raw(*, default: Any = <marshmallow.missing>, missing: Any = <marshmallow.missing>, data_key: str = None, attribute: str = None, validate: Union[Callable[[Any], Any], Iterable[Callable[[Any], Any]]] = None, required: bool = False, allow_none: bool = None, load_only: bool = False, dump_only: bool = False, error_messages: Dict[str, str] = None, **metadata)

Field that applies no formatting.

marshmallow.fields.Str

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Methods

alias of marshmallow.fields.String

class marshmallow.fields.String(*, default: Any = <marshmallow.missing>, missing: Any = <marshmallow.missing>, data_key: str = None, attribute: str = None, validate: Union[Callable[[Any], Any], Iterable[Callable[[Any], Any]]] = None, required: bool = False, allow_none: bool = None, load_only: bool = False, dump_only: bool = False, error_messages: Dict[str, str] = None, **metadata)

A string field.

Parameters

kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

_deserialize(value, attr, data, **kwargs) → Any

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs) → Optional[str]

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'invalid': 'Not a valid string.', 'invalid_utf8': 'Not a valid utf-8 string.'}

Default error messages.

class marshmallow.fields.Time(*, default: Any = <marshmallow.missing>, missing: Any = <marshmallow.missing>, data_key: str = None, attribute: str = None, validate: Union[Callable[[Any], Any], Iterable[Callable[[Any], Any]]] = None, required: bool = False, allow_none: bool = None, load_only: bool = False, dump_only: bool = False, error_messages: Dict[str, str] = None, **metadata)

ISO8601-formatted time string.

Parameters

kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize an ISO8601-formatted time to a datetime.time object.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

_deserialize(value, attr, data, **kwargs)

Deserialize an ISO8601-formatted time to a datetime.time object.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'format': '"{input}" cannot be formatted as a time.', 'invalid': 'Not a valid time.'}

Default error messages.

class marshmallow.fields.TimeDelta(precision: str = 'seconds', **kwargs)

A field that (de)serializes a datetime.timedelta object to an integer and vice versa. The integer can represent the number of days, seconds or microseconds.

Parameters

• precision – Influences how the integer is interpreted during (de)serialization. Must be ‘days’, ‘seconds’, ‘microseconds’, ‘milliseconds’, ‘minutes’, ‘hours’ or ‘weeks’.

• kwargs – The same keyword arguments that Field receives.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

Changed in version 2.0.0: Always serializes to an integer value to avoid rounding errors. Add precision parameter.

_deserialize(value, attr, data, **kwargs)

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs)

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'format': '{input!r} cannot be formatted as a timedelta.', 'invalid': 'Not a valid period of time.'}

Default error messages.

class marshmallow.fields.Tuple(tuple_fields, *args, **kwargs)

A tuple field, composed of a fixed number of other Field classes or instances

Example:

row = Tuple((fields.String(), fields.Integer(), fields.Float()))

Methods

_bind_to_schema(field_name, schema)	Update field with values from its parent schema.
_deserialize(value, attr, data, **kwargs)	Deserialize value.
_serialize(value, attr, obj, **kwargs)	Serializes value to a basic Python datatype.

Attributes

default_error_messages

Default error messages.

Note

Because of the structured nature of collections.namedtuple and typing.NamedTuple, using a Schema within a Nested field for them is more appropriate than using a Tuple field.

Parameters

• tuple_fields (Iterable[Field]) – An iterable of field classes or instances.

• kwargs – The same keyword arguments that Field receives.

New in version 3.0.0rc4.

_bind_to_schema(field_name, schema)

Update field with values from its parent schema. Called by Schema._bind_field.

Parameters

• field_name (str) – Field name set in schema.

• schema (Schema) – Parent schema.

_deserialize(value, attr, data, **kwargs) → Tuple

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_serialize(value, attr, obj, **kwargs) → Optional[Tuple]

Serializes value to a basic Python datatype. Noop by default. Concrete Field classes should implement this method.

Example:

class TitleCase(Field):
    def _serialize(self, value, attr, obj, **kwargs):
        if not value:
            return ''
        return str(value).title()

Parameters

• value – The value to be serialized.

• attr (str) – The attribute or key on the object to be serialized.

• obj (object) – The object the value was pulled from.

• kwargs (dict) – Field-specific keyword arguments.

Returns

The serialized value

default_error_messages = {'invalid': 'Not a valid tuple.'}

Default error messages.

marshmallow.fields.URL

alias of marshmallow.fields.Url

class marshmallow.fields.UUID(*, default: Any = <marshmallow.missing>, missing: Any = <marshmallow.missing>, data_key: str = None, attribute: str = None, validate: Union[Callable[[Any], Any], Iterable[Callable[[Any], Any]]] = None, required: bool = False, allow_none: bool = None, load_only: bool = False, dump_only: bool = False, error_messages: Dict[str, str] = None, **metadata)

A UUID field.

Methods

_deserialize(value, attr, data, **kwargs)	Deserialize value.
_validated(value)	Format the value or raise a ValidationError if an error occurs.

Attributes

default_error_messages

Default error messages.

_deserialize(value, attr, data, **kwargs) → Optional[uuid.UUID]

Deserialize value. Concrete Field classes should implement this method.

Parameters

• value – The value to be deserialized.

• attr – The attribute/key in data to be deserialized.

• data – The raw input data passed to the Schema.load.

• kwargs – Field-specific keyword arguments.

Raises

ValidationError – In case of formatting or validation failure.

Returns

The deserialized value.

Changed in version 2.0.0: Added attr and data parameters.

Changed in version 3.0.0: Added **kwargs to signature.

_validated(value) → Optional[uuid.UUID]

Format the value or raise a ValidationError if an error occurs.

default_error_messages = {'invalid_uuid': 'Not a valid UUID.'}

Default error messages.

class marshmallow.fields.Url(*, relative: bool = False, schemes: Union[Sequence[str], Set[str]] = None, require_tld: bool = True, **kwargs)

A validated URL field. Validation occurs during both serialization and deserialization.

Parameters

• default – Default value for the field if the attribute is not set.

• relative – Whether to allow relative URLs.

• require_tld – Whether to reject non-FQDN hostnames.

• schemes – Valid schemes. By default, http, https, ftp, and ftps are allowed.

• kwargs – The same keyword arguments that String receives.

Attributes

default_error_messages

Default error messages.

default_error_messages = {'invalid': 'Not a valid URL.'}

Default error messages.