API Reference

Schema

class marshmallow.Schema(*, only=None, exclude=(), many=False, context=None, load_only=(), dump_only=(), partial=False, unknown=None)[source]

Base schema class with which to define custom schemas.

Example usage:

import datetime as dt
from marshmallow import Schema, fields

class Album:
    def __init__(self, title, release_date):
        self.title = title
        self.release_date = release_date

class AlbumSchema(Schema):
    title = fields.Str()
    release_date = fields.Date()

# Or, equivalently
class AlbumSchema2(Schema):
    class Meta:
        fields = ("title", "release_date")

album = Album("Beggars Banquet", dt.date(1968, 12, 6))
schema = AlbumSchema()
data = schema.dump(album)
data  # {'release_date': '1968-12-06', 'title': 'Beggars Banquet'}
Parameters
  • only (tuple|list) – Whitelist of the declared fields to select when instantiating the Schema. If None, all fields are used. Nested fields can be represented with dot delimiters.

  • exclude (tuple|list) – Blacklist of the declared fields to exclude when instantiating the Schema. If a field appears in both only and exclude, it is not used. Nested fields can be represented with dot delimiters.

  • many (bool) – Should be set to True if obj is a collection so that the object will be serialized to a list.

  • context (dict) – Optional context passed to fields.Method and fields.Function fields.

  • load_only (tuple|list) – Fields to skip during serialization (write-only fields)

  • dump_only (tuple|list) – Fields to skip during deserialization (read-only fields)

  • partial (bool|tuple) – Whether to ignore missing fields and not require any fields declared. Propagates down to Nested fields as well. If its value is an iterable, only missing fields listed in that iterable will be ignored. Use dot delimiters to specify nested fields.

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

Changed in version 3.0.0: prefix parameter removed.

Changed in version 2.0.0: __validators__, __preprocessors__, and __data_handlers__ are removed in favor of marshmallow.decorators.validates_schema, marshmallow.decorators.pre_load and marshmallow.decorators.post_dump. __accessor__ and __error_handler__ are deprecated. Implement the handle_error and get_attribute methods instead.

class Meta

Options object for a Schema.

Example usage:

class Meta:
    fields = ("id", "email", "date_created")
    exclude = ("password", "secret_attribute")

Available options:

  • fields: Tuple or list of fields to include in the serialized result.

  • additional: Tuple or list of fields to include in addition to the

    explicitly declared fields. additional and fields are mutually-exclusive options.

  • include: Dictionary of additional fields to include in the schema. It is

    usually better to define fields as class variables, but you may need to use this option, e.g., if your fields are Python keywords. May be an OrderedDict.

  • exclude: Tuple or list of fields to exclude in the serialized result.

    Nested fields can be represented with dot delimiters.

  • dateformat: Default format for Date fields.

  • datetimeformat: Default format for DateTime fields.

  • render_module: Module to use for loads and dumps.

    Defaults to json from the standard library.

  • ordered: If True, order serialization output according to the

    order in which fields were declared. Output of Schema.dump will be a collections.OrderedDict.

  • index_errors: If True, errors dictionaries will include the index

    of invalid items in a collection.

  • load_only: Tuple or list of fields to exclude from serialized results.

  • dump_only: Tuple or list of fields to exclude from deserialization

  • unknown: Whether to exclude, include, or raise an error for unknown

    fields in the data. Use EXCLUDE, INCLUDE or RAISE.

  • register: Whether to register the Schema with marshmallow’s internal

    class registry. Must be True if you intend to refer to this Schema by class name in Nested fields. Only set this to False when memory usage is critical. Defaults to True.

OPTIONS_CLASS

alias of SchemaOpts

dump(obj, *, many=None)

Serialize an object to native Python data types according to this Schema’s fields.

Parameters
  • obj – The object to serialize.

  • many (bool) – Whether to serialize obj as a collection. If None, the value for self.many is used.

Returns

A dict of serialized data

Return type

dict

New in version 1.0.0.

Changed in version 3.0.0b7: This method returns the serialized data rather than a (data, errors) duple. A ValidationError is raised if obj is invalid.

Changed in version 3.0.0rc9: Validation no longer occurs upon serialization.

dumps(obj, *args, many=None, **kwargs)

Same as dump(), except return a JSON-encoded string.

Parameters
  • obj – The object to serialize.

  • many (bool) – Whether to serialize obj as a collection. If None, the value for self.many is used.

Returns

A json string

Return type

str

New in version 1.0.0.

Changed in version 3.0.0b7: This method returns the serialized data rather than a (data, errors) duple. A ValidationError is raised if obj is invalid.

classmethod from_dict(fields: Dict[str, marshmallow.fields.Field], *, name: str = 'GeneratedSchema') → Type[marshmallow.schema.Schema]

Generate a Schema class given a dictionary of fields.

from marshmallow import Schema, fields

PersonSchema = Schema.from_dict({"name": fields.Str()})
print(PersonSchema().load({"name": "David"}))  # => {'name': 'David'}

Generated schemas are not added to the class registry and therefore cannot be referred to by name in Nested fields.

Parameters
  • fields (dict) – Dictionary mapping field names to field instances.

  • name (str) – Optional name for the class, which will appear in the repr for the class.

New in version 3.0.0.

get_attribute(obj, attr, default)

Defines how to pull values from an object to serialize.

New in version 2.0.0.

Changed in version 3.0.0a1: Changed position of obj and attr.

handle_error(error, data, *, many, **kwargs)

Custom error handler function for the schema.

Parameters
  • error (ValidationError) – The ValidationError raised during (de)serialization.

  • data – The original input data.

  • many (bool) – Value of many on dump or load.

  • partial (bool) – Value of partial on load.

New in version 2.0.0.

Changed in version 3.0.0rc9: Receives many and partial (on deserialization) as keyword arguments.

load(data, *, many=None, partial=None, unknown=None)

Deserialize a data structure to an object defined by this Schema’s fields.

Parameters
  • data (dict) – The data to deserialize.

  • many (bool) – Whether to deserialize data as a collection. If None, the value for self.many is used.

  • partial (bool|tuple) – Whether to ignore missing fields and not require any fields declared. Propagates down to Nested fields as well. If its value is an iterable, only missing fields listed in that iterable will be ignored. Use dot delimiters to specify nested fields.

  • unknown – Whether to exclude, include, or raise an error for unknown fields in the data. Use EXCLUDE, INCLUDE or RAISE. If None, the value for self.unknown is used.

Returns

A dict of deserialized data

Return type

dict

New in version 1.0.0.

Changed in version 3.0.0b7: This method returns the deserialized data rather than a (data, errors) duple. A ValidationError is raised if invalid data are passed.

loads(json_data, *, many=None, partial=None, unknown=None, **kwargs)

Same as load(), except it takes a JSON string as input.

Parameters
  • json_data (str) – A JSON string of the data to deserialize.

  • many (bool) – Whether to deserialize obj as a collection. If None, the value for self.many is used.

  • partial (bool|tuple) – Whether to ignore missing fields and not require any fields declared. Propagates down to Nested fields as well. If its value is an iterable, only missing fields listed in that iterable will be ignored. Use dot delimiters to specify nested fields.

  • unknown – Whether to exclude, include, or raise an error for unknown fields in the data. Use EXCLUDE, INCLUDE or RAISE. If None, the value for self.unknown is used.

Returns

A dict of deserialized data

Return type

dict

New in version 1.0.0.

Changed in version 3.0.0b7: This method returns the deserialized data rather than a (data, errors) duple. A ValidationError is raised if invalid data are passed.

on_bind_field(field_name, field_obj)

Hook to modify a field when it is bound to the Schema.

No-op by default.

validate(data, *, many=None, partial=None)

Validate data against the schema, returning a dictionary of validation errors.

Parameters
  • data (dict) – The data to validate.

  • many (bool) – Whether to validate data as a collection. If None, the value for self.many is used.

  • partial (bool|tuple) – Whether to ignore missing fields and not require any fields declared. Propagates down to Nested fields as well. If its value is an iterable, only missing fields listed in that iterable will be ignored. Use dot delimiters to specify nested fields.

Returns

A dictionary of validation errors.

Return type

dict

New in version 1.1.0.

class marshmallow.SchemaOpts(meta, ordered=False)[source]

class Meta options for the Schema. Defines defaults.

Fields

Field classes for various types of data.

class marshmallow.fields.Field(*, default=<marshmallow.missing>, missing=<marshmallow.missing>, data_key=None, attribute=None, validate=None, required=False, allow_none=None, load_only=False, dump_only=False, error_messages=None, **metadata)[source]

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 (str) – 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 (str) – 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 (callable) – 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 (bool) – If True skip this field during serialization, otherwise its value will be present in the serialized data.

  • dump_only (bool) – 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.

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)[source]

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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)[source]

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

_validate_missing(value)[source]

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.fail. The values are error messages passed to marshmallow.exceptions.ValidationError.

deserialize(value, attr=None, data=None, **kwargs)[source]

Deserialize value.

Parameters
  • value – The value to deserialize.

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

  • data (dict) – The raw input data passed to Schema.load.

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

Raises

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

fail(key: str, **kwargs)[source]

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>)[source]

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[source]

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, obj, accessor=None, **kwargs)[source]

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

Parameters
  • attr (str) – The attribute/key to get from the object.

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

  • accessor (callable) – Function used to access values from obj.

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

class marshmallow.fields.Raw(*, default=<marshmallow.missing>, missing=<marshmallow.missing>, data_key=None, attribute=None, validate=None, required=False, allow_none=None, load_only=False, dump_only=False, error_messages=None, **metadata)[source]

Field that applies no formatting or validation.

class marshmallow.fields.Nested(nested, *, default=<marshmallow.missing>, exclude=(), only=None, **kwargs)[source]

Allows you to nest a Schema inside a field.

Examples:

user = fields.Nested(UserSchema)
user2 = fields.Nested('UserSchema')  # Equivalent to above
collaborators = fields.Nested(UserSchema, many=True, only=('id',))
parent = fields.Nested('self')

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

  • exclude (tuple) – 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 (bool) – 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, many=False, **kwargs)[source]

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, many=False, **kwargs)[source]

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

property schema

The nested Schema object.

Changed in version 1.0.0: Renamed from serializer to schema.

class marshmallow.fields.Mapping(keys=None, values=None, **kwargs)[source]

An abstract class for objects with key-value pairs.

Parameters
  • keys (Field) – A field class or instance for dict keys.

  • values (Field) – A field class or instance for dict values.

  • kwargs – The same keyword arguments that Field receives.

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)[source]

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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

mapping_type

alias of builtins.dict

class marshmallow.fields.Dict(keys=None, values=None, **kwargs)[source]

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())
Parameters

kwargs – The same keyword arguments that Mapping receives.

New in version 2.1.0.

mapping_type

alias of builtins.dict

class marshmallow.fields.List(cls_or_instance, **kwargs)[source]

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

Example:

numbers = fields.List(fields.Float())
Parameters
  • cls_or_instance (Field) – A field class or instance.

  • default (bool) – Default value for serialization.

  • 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)[source]

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.Tuple(tuple_fields, *args, **kwargs)[source]

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

Example:

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

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)[source]

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.String(*, default=<marshmallow.missing>, missing=<marshmallow.missing>, data_key=None, attribute=None, validate=None, required=False, allow_none=None, load_only=False, dump_only=False, error_messages=None, **metadata)[source]

A string field.

Parameters

kwargs – The same keyword arguments that Field receives.

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.UUID(*, default=<marshmallow.missing>, missing=<marshmallow.missing>, data_key=None, attribute=None, validate=None, required=False, allow_none=None, load_only=False, dump_only=False, error_messages=None, **metadata)[source]

A UUID field.

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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

_validated(value)[source]

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

class marshmallow.fields.Number(*, as_string=False, **kwargs)[source]

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.

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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

_serialize(value, attr, obj, **kwargs)[source]

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

_validated(value)[source]

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

num_type

alias of builtins.float

class marshmallow.fields.Integer(*, strict=False, **kwargs)[source]

An integer field.

Parameters

kwargs – The same keyword arguments that Number receives.

_validated(value)[source]

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

num_type

alias of builtins.int

class marshmallow.fields.Decimal(places=None, rounding=None, *, allow_nan=False, as_string=False, **kwargs)[source]

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.

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

  • as_string (bool) – 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)[source]

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

_validated(value)[source]

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

num_type

alias of decimal.Decimal

class marshmallow.fields.Boolean(*, truthy=None, falsy=None, **kwargs)[source]

A boolean field.

Parameters
_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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

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

Default falsy values.

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

Default truthy values.

class marshmallow.fields.Float(*, allow_nan=False, as_string=False, **kwargs)[source]

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.

_validated(value)[source]

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

num_type

alias of builtins.float

class marshmallow.fields.DateTime(format=None, **kwargs)[source]

A formatted datetime string.

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

Parameters
  • format (str) – 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.

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

_bind_to_schema(field_name, schema)[source]

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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=None, *, timezone=None, **kwargs)[source]

A formatted naive datetime string.

Parameters
  • format (str) – See DateTime.

  • timezone (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.

New in version 3.0.0rc9.

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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.AwareDateTime(format=None, *, default_timezone=None, **kwargs)[source]

A formatted aware datetime string.

Parameters
  • format (str) – See DateTime.

  • default_timezone (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.

New in version 3.0.0rc9.

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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.Time(*, default=<marshmallow.missing>, missing=<marshmallow.missing>, data_key=None, attribute=None, validate=None, required=False, allow_none=None, load_only=False, dump_only=False, error_messages=None, **metadata)[source]

ISO8601-formatted time string.

Parameters

kwargs – The same keyword arguments that Field receives.

_deserialize(value, attr, data, **kwargs)[source]

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

_serialize(value, attr, obj, **kwargs)[source]

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=None, **kwargs)[source]

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.

class marshmallow.fields.TimeDelta(precision='seconds', **kwargs)[source]

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 (str) – 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.

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

_deserialize(value, attr, data, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.Url(*, relative=False, schemes=None, require_tld=True, **kwargs)[source]

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

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

  • attribute (str) – The name of the attribute to get the value from. If None, assumes the attribute has the same name as the field.

  • relative (bool) – Whether to allow relative URLs.

  • require_tld (bool) – Whether to reject non-FQDN hostnames.

  • kwargs – The same keyword arguments that String receives.

marshmallow.fields.URL

alias of marshmallow.fields.Url

class marshmallow.fields.Email(*args, **kwargs)[source]

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.

class marshmallow.fields.Method(serialize=None, deserialize=None, **kwargs)[source]

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.

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.Function(serialize=None, deserialize=None, **kwargs)[source]

A field that takes the value returned by a function.

Parameters
  • serialize (callable) – 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 (callable) – 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.

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)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.Str

alias of marshmallow.fields.String

marshmallow.fields.Bool

alias of marshmallow.fields.Boolean

marshmallow.fields.Int

alias of marshmallow.fields.Integer

class marshmallow.fields.Constant(constant, **kwargs)[source]

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.

New in version 2.0.0.

_deserialize(value, *args, **kwargs)[source]

Deserialize value. Concrete Field classes should implement this method.

Parameters
  • value – The value to be deserialized.

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

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

  • kwargs (dict) – 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)[source]

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.Pluck(nested, field_name, **kwargs)[source]

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}
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)[source]

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)[source]

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

Decorators

Decorators for registering schema pre-processing and post-processing methods. These should be imported from the top-level marshmallow module.

Example:

from marshmallow import (
    Schema, pre_load, pre_dump, post_load, validates_schema,
    validates, fields, ValidationError
)

class UserSchema(Schema):

    email = fields.Str(required=True)
    age = fields.Integer(required=True)

    @post_load
    def lowerstrip_email(self, item, **kwargs):
        item['email'] = item['email'].lower().strip()
        return item

    @pre_load(pass_many=True)
    def remove_envelope(self, data, many, **kwargs):
        namespace = 'results' if many else 'result'
        return data[namespace]

    @post_dump(pass_many=True)
    def add_envelope(self, data, many, **kwargs):
        namespace = 'results' if many else 'result'
        return {namespace: data}

    @validates_schema
    def validate_email(self, data, **kwargs):
        if len(data['email']) < 3:
            raise ValidationError('Email must be more than 3 characters', 'email')

    @validates('age')
    def validate_age(self, data, **kwargs):
        if data < 14:
            raise ValidationError('Too young!')

Note

These decorators only work with instance methods. Class and static methods are not supported.

Warning

The invocation order of decorated methods of the same type is not guaranteed. If you need to guarantee order of different processing steps, you should put them in the same processing method.

marshmallow.decorators.post_dump(fn=None, pass_many=False, pass_original=False)[source]

Register a method to invoke after serializing an object. The method receives the serialized object and returns the processed object.

By default, receives a single object at a time, transparently handling the many argument passed to the Schema. If pass_many=True, the raw data (which may be a collection) and the value for many is passed.

If pass_original=True, the original data (before serializing) will be passed as an additional argument to the method.

Changed in version 3.0.0: many is always passed as a keyword arguments to the decorated method.

marshmallow.decorators.post_load(fn=None, pass_many=False, pass_original=False)[source]

Register a method to invoke after deserializing an object. The method receives the deserialized data and returns the processed data.

By default, receives a single datum at a time, transparently handling the many argument passed to the Schema. If pass_many=True, the raw data (which may be a collection) and the value for many is passed.

If pass_original=True, the original data (before deserializing) will be passed as an additional argument to the method.

Changed in version 3.0.0: partial and many are always passed as keyword arguments to the decorated method.

marshmallow.decorators.pre_dump(fn=None, pass_many=False)[source]

Register a method to invoke before serializing an object. The method receives the object to be serialized and returns the processed object.

By default, receives a single object at a time, regardless of whether many=True is passed to the Schema. If pass_many=True, the raw data (which may be a collection) and the value for many is passed.

Changed in version 3.0.0: many is always passed as a keyword arguments to the decorated method.

marshmallow.decorators.pre_load(fn=None, pass_many=False)[source]

Register a method to invoke before deserializing an object. The method receives the data to be deserialized and returns the processed data.

By default, receives a single datum at a time, transparently handling the many argument passed to the Schema. If pass_many=True, the raw data (which may be a collection) and the value for many is passed.

Changed in version 3.0.0: partial and many are always passed as keyword arguments to the decorated method.

marshmallow.decorators.set_hook(fn, key, **kwargs)[source]

Mark decorated function as a hook to be picked up later.

Note

Currently only works with functions and instance methods. Class and static methods are not supported.

Returns

Decorated function if supplied, else this decorator with its args bound.

marshmallow.decorators.validates(field_name)[source]

Register a field validator.

Parameters

field_name (str) – Name of the field that the method validates.

marshmallow.decorators.validates_schema(fn=None, pass_many=False, pass_original=False, skip_on_field_errors=True)[source]

Register a schema-level validator.

By default, receives a single object at a time, regardless of whether many=True is passed to the Schema. If pass_many=True, the raw data (which may be a collection) and the value for many is passed.

If pass_original=True, the original data (before unmarshalling) will be passed as an additional argument to the method.

If skip_on_field_errors=True, this validation method will be skipped whenever validation errors have been detected when validating fields.

Changed in version 3.0.0b1: skip_on_field_errors defaults to True.

Changed in version 3.0.0: partial and many are always passed as keyword arguments to the decorated method.

Validators

Validation classes for various types of data.

class marshmallow.validate.ContainsOnly(choices, labels=None, *, error=None)[source]

Validator which succeeds if value is a sequence and each element in the sequence is also in the sequence passed as choices. Empty input is considered valid.

Parameters
  • choices (iterable) – Same as OneOf.

  • labels (iterable) – Same as OneOf.

  • error (str) – Same as OneOf.

Changed in version 3.0.0b2: Duplicate values are considered valid.

Changed in version 3.0.0b2: Empty input is considered valid. Use validate.Length(min=1) to validate against empty inputs.

class marshmallow.validate.Email(*, error=None)[source]

Validate an email address.

Parameters

error (str) – Error message to raise in case of a validation error. Can be interpolated with {input}.

class marshmallow.validate.Equal(comparable, *, error=None)[source]

Validator which succeeds if the value passed to it is equal to comparable.

Parameters
  • comparable – The object to compare to.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input} and {other}.

class marshmallow.validate.Length(min=None, max=None, *, error=None, equal=None)[source]

Validator which succeeds if the value passed to it has a length between a minimum and maximum. Uses len(), so it can work for strings, lists, or anything with length.

Parameters
  • min (int) – The minimum length. If not provided, minimum length will not be checked.

  • max (int) – The maximum length. If not provided, maximum length will not be checked.

  • equal (int) – The exact length. If provided, maximum and minimum length will not be checked.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input}, {min} and {max}.

class marshmallow.validate.NoneOf(iterable, *, error=None)[source]

Validator which fails if value is a member of iterable.

Parameters
  • iterable (iterable) – A sequence of invalid values.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated using {input} and {values}.

class marshmallow.validate.OneOf(choices, labels=None, *, error=None)[source]

Validator which succeeds if value is a member of choices.

Parameters
  • choices (iterable) – A sequence of valid values.

  • labels (iterable) – Optional sequence of labels to pair with the choices.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input}, {choices} and {labels}.

options(valuegetter=<class 'str'>)[source]

Return a generator over the (value, label) pairs, where value is a string associated with each choice. This convenience method is useful to populate, for instance, a form select field.

Parameters

valuegetter – Can be a callable or a string. In the former case, it must be a one-argument callable which returns the value of a choice. In the latter case, the string specifies the name of an attribute of the choice objects. Defaults to str() or str().

class marshmallow.validate.Predicate(method, *, error=None, **kwargs)[source]

Call the specified method of the value object. The validator succeeds if the invoked method returns an object that evaluates to True in a Boolean context. Any additional keyword argument will be passed to the method.

Parameters
  • method (str) – The name of the method to invoke.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input} and {method}.

  • kwargs – Additional keyword arguments to pass to the method.

class marshmallow.validate.Range(min=None, max=None, *, min_inclusive=True, max_inclusive=True, error=None)[source]

Validator which succeeds if the value passed to it is within the specified range. If min is not specified, or is specified as None, no lower bound exists. If max is not specified, or is specified as None, no upper bound exists. The inclusivity of the bounds (if they exist) is configurable. If min_inclusive is not specified, or is specified as True, then the min bound is included in the range. If max_inclusive is not specified, or is specified as True, then the max bound is included in the range.

Parameters
  • min – The minimum value (lower bound). If not provided, minimum value will not be checked.

  • max – The maximum value (upper bound). If not provided, maximum value will not be checked.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input}, {min} and {max}.

  • min_inclusive (bool) – Whether the min bound is included in the range.

  • max_inclusive (bool) – Whether the max bound is included in the range.

class marshmallow.validate.Regexp(regex, flags=0, *, error=None)[source]

Validator which succeeds if the value matches regex.

Note

Uses re.match, which searches for a match at the beginning of a string.

Parameters
  • regex – The regular expression string to use. Can also be a compiled regular expression pattern.

  • flags – The regexp flags to use, for example re.IGNORECASE. Ignored if regex is not a string.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input} and {regex}.

class marshmallow.validate.URL(*, relative=False, schemes=None, require_tld=True, error=None)[source]

Validate a URL.

Parameters
  • relative (bool) – Whether to allow relative URLs.

  • error (str) – Error message to raise in case of a validation error. Can be interpolated with {input}.

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

  • require_tld (bool) – Whether to reject non-FQDN hostnames.

class marshmallow.validate.Validator[source]

Base abstract class for validators.

Note

This class does not provide any behavior. It is only used to add a useful __repr__ implementation for validators.

Utility Functions

Utility methods for marshmallow.

marshmallow.utils.callable_or_raise(obj)[source]

Check that an object is callable, else raise a ValueError.

marshmallow.utils.from_iso_date(value)[source]

Parse a string and return a datetime.date.

marshmallow.utils.from_iso_datetime(value)[source]

Parse a string and return a datetime.datetime.

This function supports time zone offsets. When the input contains one, the output uses a timezone with a fixed offset from UTC.

marshmallow.utils.from_iso_time(value)[source]

Parse a string and return a datetime.time.

This function doesn’t support time zone offsets.

marshmallow.utils.from_rfc(datestring)[source]

Parse a RFC822-formatted datetime string and return a datetime object.

https://stackoverflow.com/questions/885015/how-to-parse-a-rfc-2822-date-time-into-a-python-datetime # noqa: B950

marshmallow.utils.get_fixed_timezone(offset)[source]

Return a tzinfo instance with a fixed offset from UTC.

marshmallow.utils.get_func_args(func: Callable) → List[str][source]

Given a callable, return a list of argument names. Handles functools.partial objects and class-based callables.

Changed in version 3.0.0a1: Do not return bound arguments, eg. self.

marshmallow.utils.get_value(obj, key, default=<marshmallow.missing>)[source]

Helper for pulling a keyed value off various types of objects. Fields use this method by default to access attributes of the source object. For object x and attribute i, this method first tries to access x[i], and then falls back to x.i if an exception is raised.

Warning

If an object x does not raise an exception when x[i] does not exist, get_value will never check the value x.i. Consider overriding marshmallow.fields.Field.get_value in this case.

marshmallow.utils.is_collection(obj)[source]

Return True if obj is a collection type, e.g list, tuple, queryset.

marshmallow.utils.is_generator(obj)[source]

Return True if obj is a generator

marshmallow.utils.is_instance_or_subclass(val, class_)[source]

Return True if val is either a subclass or instance of class_.

marshmallow.utils.is_iterable_but_not_string(obj)[source]

Return True if obj is an iterable object that isn’t a string.

marshmallow.utils.is_keyed_tuple(obj)[source]

Return True if obj has keyed tuple behavior, such as namedtuples or SQLAlchemy’s KeyedTuples.

marshmallow.utils.isoformat(datetime)[source]

Return the ISO8601-formatted representation of a datetime object.

Parameters

datetime (datetime) – The datetime.

marshmallow.utils.pluck(dictlist, key)[source]

Extracts a list of dictionary values from a list of dictionaries.

>>> dlist = [{'id': 1, 'name': 'foo'}, {'id': 2, 'name': 'bar'}]
>>> pluck(dlist, 'id')
[1, 2]
marshmallow.utils.pprint(obj, *args, **kwargs)[source]

Pretty-printing function that can pretty-print OrderedDicts like regular dictionaries. Useful for printing the output of marshmallow.Schema.dump().

marshmallow.utils.resolve_field_instance(cls_or_instance)[source]

Return a Schema instance from a Schema class or instance.

Parameters

cls_or_instance (type|Schema) – Marshmallow Schema class or instance.

marshmallow.utils.rfcformat(datetime)[source]

Return the RFC822-formatted representation of a datetime object.

Parameters

datetime (datetime) – The datetime.

marshmallow.utils.set_value(dct, key, value)[source]

Set a value in a dict. If key contains a ‘.’, it is assumed be a path (i.e. dot-delimited string) to the value’s location.

>>> d = {}
>>> set_value(d, 'foo.bar', 42)
>>> d
{'foo': {'bar': 42}}

Error Store

Utilities for storing collections of error messages.

Warning

This module is treated as private API. Users should not need to use this module directly.

marshmallow.error_store.merge_errors(errors1, errors2)[source]

Deeply merge two error messages.

The format of errors1 and errors2 matches the message parameter of marshmallow.exceptions.ValidationError.

Class Registry

A registry of Schema classes. This allows for string lookup of schemas, which may be used with class:fields.Nested.

Warning

This module is treated as private API. Users should not need to use this module directly.

marshmallow.class_registry.get_class(classname, all=False)[source]

Retrieve a class from the registry.

Raises

marshmallow.exceptions.RegistryError if the class cannot be found or if there are multiple entries for the given class name.

marshmallow.class_registry.register(classname, cls)[source]

Add a class to the registry of serializer classes. When a class is registered, an entry for both its classname and its full, module-qualified path are added to the registry.

Example:

class MyClass:
    pass

register('MyClass', MyClass)
# Registry:
# {
#   'MyClass': [path.to.MyClass],
#   'path.to.MyClass': [path.to.MyClass],
# }

Exceptions

Exception classes for marshmallow-related errors.

exception marshmallow.exceptions.FieldInstanceResolutionError[source]

Raised when schema to instantiate is neither a Schema class nor an instance.

exception marshmallow.exceptions.MarshmallowError[source]

Base class for all marshmallow-related errors.

exception marshmallow.exceptions.RegistryError[source]

Raised when an invalid operation is performed on the serializer class registry.

exception marshmallow.exceptions.StringNotCollectionError[source]

Raised when a string is passed when a list of strings is expected.

exception marshmallow.exceptions.ValidationError(message, field_name='_schema', data=None, valid_data=None, **kwargs)[source]

Raised when validation fails on a field or schema.

Validators and custom fields should raise this exception.

Parameters
  • message (str|list|dict) – An error message, list of error messages, or dict of error messages. If a dict, the keys are subitems and the values are error messages.

  • field_name (str) – Field name to store the error on. If None, the error is stored as schema-level error.

  • data (dict) – Raw input data.

  • valid_data (dict) – Valid (de)serialized data.