API Reference

Data

lollipop.types.MISSING = <MISSING>

Special singleton value (like None) to represent case when value is missing.

Types

class lollipop.types.Type(validate=None, *args, **kwargs)

Base class for defining data types.

Parameters:validate (list) – A validator or list of validators for this data type. Validator is a callable that takes serialized data and raises ValidationError if data is invalid. Validator return value is ignored.

dump(value, context=None)

Serialize data to primitive types. Raises ValidationError if data is invalid.

Parameters:

• value – Value to serialize.
• context – Context data.

load(data, context=None)

Deserialize data from primitive types. Raises ValidationError if data is invalid.

Parameters:

• data – Data to deserialize.
• context – Context data.

validate(data, context=None)

Takes serialized data and returns validation errors or None.

Parameters:

• data – Data to validate.
• context – Context data.

class lollipop.types.Any(validate=None, *args, **kwargs)

Any type. Does not transform/validate given data.

class lollipop.types.String(validate=None, *args, **kwargs)

A string type.

class lollipop.types.Integer(validate=None, *args, **kwargs)

An integer type.

num_type

alias of int

class lollipop.types.Float(validate=None, *args, **kwargs)

A float type.

num_type

alias of float

class lollipop.types.Boolean(validate=None, *args, **kwargs)

A boolean type.

class lollipop.types.List(item_type, **kwargs)

A homogenous list type.

Example:

List(String()).load(['foo', 'bar', 'baz'])

Parameters:

• item_type (Type) – Type of list elements.
• kwargs – Same keyword arguments as for Type.

class lollipop.types.Tuple(item_types, **kwargs)

A heterogenous list type.

Example:

Tuple([String(), Integer(), Boolean()]).load(['foo', 123, False])

Parameters:

• item_types (list) – List of item types.
• kwargs – Same keyword arguments as for Type.

class lollipop.types.Dict(value_types=<Any>, **kwargs)

A dict type. You can specify either a single type for all dict values or provide a dict-like mapping object that will return proper Type instance for each given dict key.

Example:

Dict(Integer()).load({'key0': 1, 'key1': 5, 'key2': 15})

Dict({'foo': String(), 'bar': Integer()}).load({
    'foo': 'hello', 'bar': 123,
})

Parameters:

• value_type (dict) – A single Type for all dict values or mapping of allowed keys to Type instances.
• kwargs – Same keyword arguments as for Type.

class lollipop.types.OneOf(types, load_hint=<function type_name_hint>, dump_hint=<function type_name_hint>, *args, **kwargs)

Example:

class Foo(object):
    def __init__(self, foo):
        self.foo = foo

class Bar(object):
    def __init__(self, bar):
        self.bar = bar

FooType = Object({'foo': String()}, constructor=Foo)
BarType = Object({'bar': Integer()}, constructor=Bar)

def object_with_type(name, subject_type):
    return Object(subject_type, {'type': name},
                  constructor=subject_type.constructor)

FooBarType = OneOf({
    'Foo': object_with_type('Foo', FooType),
    'Bar': object_with_type('Bar', BarType),
}, dump_hint=type_name_hint, load_hint=dict_value_hint('type'))

List(FooBarType).dump([Foo(foo='hello'), Bar(bar=123)])
# => [{'type': 'Foo', 'foo': 'hello'}, {'type': 'Bar', 'bar': 123}]

List(FooBarType).load([{'type': 'Foo', 'foo': 'hello'},
                       {'type': 'Bar', 'bar': 123}])
# => [Foo(foo='hello'), Bar(bar=123)]

lollipop.types.type_name_hint(data)

Returns type name of given value.

To be used as a type hint in OneOf.

lollipop.types.dict_value_hint(key, mapper=None)

Returns a function that takes a dictionary and returns value of particular key. The returned value can be optionally processed by mapper function.

To be used as a type hint in OneOf.

class lollipop.types.Field(field_type, *args, **kwargs)

Base class for describing Object fields. Defines a way to access object fields during serialization/deserialization. Usually it extracts data to serialize/deserialize and call self.field_type.load() to do data transformation.

Parameters:field_type (Type) – Field type.

dump(name, obj, *args, **kwargs)

Serialize data to primitive types. Raises ValidationError if data is invalid.

Parameters:

• name (str) – Name of attribute to serialize.
• obj – Application object to extract serialized value from.

load(name, data, *args, **kwargs)

Deserialize data from primitive types. Raises ValidationError if data is invalid.

Parameters:

• name (str) – Name of attribute to deserialize.
• data – Raw data to get value to deserialize from.

class lollipop.types.ConstantField(field_type, value, *args, **kwargs)

Field that always serializes to given value and does not deserialize.

Parameters:

• field_type (Type) – Field type.
• value – Value constant for this field.

class lollipop.types.AttributeField(field_type, attribute=None, *args, **kwargs)

Field that corresponds to object attribute.

Parameters:

• field_type (Type) – Field type.
• attribute (str) – Use given attribute name instead of field name defined in object type.

class lollipop.types.MethodField(field_type, method, *args, **kwargs)

Field that is result of method invocation.

Example:

class Person(object):
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    def get_name(self):
        return self.first_name + ' ' + self.last_name

PersonType = Object({
    'name': MethodField(String(), 'get_name'),
}, constructor=Person)

Parameters:

• field_type (Type) – Field type.
• method (str) – Method name. Method should not take any arguments.

class lollipop.types.FunctionField(field_type, function, *args, **kwargs)

Field that is result of function invocation.

Example:

class Person(object):
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

def get_name(person):
    return person.first_name + ' ' + person.last_name

PersonType = Object({
    'name': FunctionField(String(), get_name),
}, constructor=Person)

Parameters:

• field_type (Type) – Field type.
• function (callable) – Function that takes source object and returns field value.

class lollipop.types.Object(bases_or_fields=None, fields=None, constructor=<type 'dict'>, default_field_type=<class 'lollipop.types.AttributeField'>, allow_extra_fields=True, only=None, exclude=None, **kwargs)

An object type. Serializes to a dict of field names to serialized field values. Parametrized with field names to types mapping. The way values are obtained during serialization is determined by type of field object in fields mapping (see ConstantField, AttributeField, MethodField for details). You can specify either Field object, a Type object or any other value. In case of Type, it will be automatically wrapped with a default field type, which is controlled by default_field_type constructor argument. In case of any other value it will be transformed into ConstantField.

Example:

class Person(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age

PersonType = Object({
    'name': String(),
    'age': Integer(),
}, constructor=Person)
PersonType.load({'name': 'John', 'age': 42})
# => Person(name='John', age=42)

Parameters:

• base_or_fields – Either Object instance or fields (See fields argument). In case of fields, the actual fields argument should not be specified.
• fields – List of name-to-value tuples or mapping of object field names to Type, Field objects or constant values.
• contructor (callable) – Deserialized value constructor. Constructor should take all fields values as keyword arguments.
• default_field_type (Field) – Default field type to use for fields defined by their type.
• allow_extra_fields (bool) – If False, it will raise ValidationError for all extra dict keys during deserialization. If True, will ignore all extra fields.
• only (list) – List of field names to include in this object. All other fields (own or inherited) won’t be used.
• exclude (list) – List of field names to exclude from this object. All other fields (own or inherited) will be included.
• kwargs – Same keyword arguments as for Type.

class lollipop.types.Optional(inner_type, load_default=None, dump_default=None, **kwargs)

A wrapper type which makes values optional: if value is missing or None, it will not transform it with an inner type but instead will return None (or any other configured value).

Example:

UserType = Object({
    'email': String(),           # by default types require valid values
    'name': Optional(String()),  # value can be omitted or None
    'role': Optional(            # when value is omitted or None, use given value
        String(validate=AnyOf(['admin', 'customer'])),
        load_default='customer',
    ),
})

Parameters:

• inner_type (Type) – Actual type that should be optional.
• load_default – Value to use when value is missing on deserialization.
• dump_default – Value to use when value is missing on serialization.
• kwargs – Same keyword arguments as for Type.

class lollipop.types.LoadOnly(inner_type)

A wrapper type which proxies loading to inner type but always returns MISSING on dump.

Example:

UserType = Object({
    'name': String(),
    'password': LoadOnly(String()),
})

Parameters:inner_type (Type) – Data type.

class lollipop.types.DumpOnly(inner_type)

A wrapper type which proxies dumping to inner type but always returns MISSING on load.

Example:

UserType = Object({
    'name': String(),
    'created_at': DumpOnly(DateTime()),
})

Parameters:inner_type (Type) – Data type.

Validators

class lollipop.validators.Validator(error_messages=None, *args, **kwargs)

Base class for all validators.

Validator is used by types to validate data during deserialization. Validator class should define __call__ method with either one or two arguments. In both cases, first argument is value being validated. In case of two arguments, the second one is the context. If given value fails validation, __call__ method should raise ValidationError. Return value is always ignored.

class lollipop.validators.Predicate(predicate, error=None, **kwargs)

Validator that succeeds if given predicate returns True.

Parameters:

• predicate (callable) – Predicate that takes value and returns True or False. One- and two-argument predicates are supported. First argument in both cases is value being validated. In case of two arguments, the second one is context.
• error (str) – Error message in case of validation error. Can be interpolated with data.

class lollipop.validators.Range(min=None, max=None, **kwargs)

Validator that checks value is in given range.

Parameters:

• min (int) – Minimum length. If not provided, minimum won’t be checked.
• max (int) – Maximum length. If not provided, maximum won’t be checked.
• error (str) – Error message in case of validation error. Can be interpolated with data, min or max.

class lollipop.validators.Length(exact=None, min=None, max=None, **kwargs)

Validator that checks value length (using len()) to be in given range.

Parameters:

• exact (int) – Exact length. If provided, min and max are not checked. If not provided, min and max checks are performed.
• min (int) – Minimum length. If not provided, minimum length won’t be checked.
• max (int) – Maximum length. If not provided, maximum length won’t be checked.
• error (str) – Error message in case of validation error. Can be interpolated with data, length, exact, min or max.

class lollipop.validators.NoneOf(values, error=None, **kwargs)

Validator that succeeds if value is not a member of given values.

Parameters:

• values (iterable) – A sequence of invalid values.
• error (str) – Error message in case of validation error. Can be interpolated with data and values.

class lollipop.validators.AnyOf(choices, error=None, **kwargs)

Validator that succeeds if value is a member of given choices.

Parameters:

• choices (iterable) – A sequence of allowed values.
• error (str) – Error message in case of validation error. Can be interpolated with data and choices.

class lollipop.validators.Regexp(regexp, flags=0, error=None, **kwargs)

Validator that succeeds if value matches given regex.

Parameters:

• regexp (str) – Regular expression string.
• flags (int) – Regular expression flags, e.g. re.IGNORECASE. Not used if regexp is not a string.
• error (str) – Error message in case of validation error. Can be interpolated with data and regexp.

Errors

lollipop.errors.SCHEMA = '_schema'

Name of an error key for cases when you have both errors for the object and for it’s fields:

{'field1': 'Field error', '_schema': 'Whole object error'}

exception lollipop.errors.ValidationError(messages)

Exception to report validation errors.

Examples of valid error messages:

raise ValidationError('Error')
raise ValidationError(['Error 1', 'Error 2'])
raise ValidationError({
    'field1': 'Error 1',
    'field2': {'subfield1': ['Error 2', 'Error 3']}
})

Parameters:messages – Validation error messages. String, list of strings or dict where keys are nested fields and values are error messages.

class lollipop.errors.ValidationErrorBuilder

Helper class to report multiple errors.

Example:

def validate_all(data):
    builder = ValidationErrorBuilder()
    if data['foo']['bar'] >= data['baz']['bam']:
        builder.add_error('foo.bar', 'Should be less than bam')
    if data['foo']['quux'] >= data['baz']['bam']:
        builder.add_fields('foo.quux', 'Should be less than bam')
    ...
    builder.raise_errors()

add_error(path, error)

Add error message for given field path.

Example:

builder = ValidationErrorBuilder()
builder.add_error('foo.bar.baz', 'Some error')
print builder.errors
# => {'foo': {'bar': {'baz': 'Some error'}}}

Parameters:

• path (str) – ‘.’-separated list of field names
• error (str) – Error message

add_errors(errors)

Add errors in dict format.

Example:

builder = ValidationErrorBuilder()
builder.add_errors({'foo': {'bar': 'Error 1'}})
builder.add_errors({'foo': {'baz': 'Error 2'}, 'bam': 'Error 3'})
print builder.errors
# => {'foo': {'bar': 'Error 1', 'baz': 'Error 2'}, 'bam': 'Error 3'}

Parameters:list or dict errors (str,) – Errors to merge

raise_errors()

Raise ValidationError if errors are not empty; do nothing otherwise.

lollipop.errors.merge_errors(errors1, errors2)

Deeply merges two error messages. Error messages can be string, list of strings or dict of error messages (recursively). Format is the same as accepted by ValidationError. Returns new error messages.