"""Model descriptions.
The model describes the components of a data structure, kind of like a struct
in C, but there's no limitation of what type of data structure the model is,
or what it's used for.
A record (faust.models.record) is a model type that serialize into
dictionaries, so the model describe the fields, and their types:
.. sourcecode:: pycon
>>> class Point(Record):
... x: int
... y: int
>>> p = Point(10, 3)
>>> assert p.x == 10
>>> assert p.y == 3
>>> p
<Point: x=10, y=3>
>>> payload = p.dumps(serializer='json')
'{"x": 10, "y": 3, "__faust": {"ns": "__main__.Point"}}'
>>> p2 = Record.loads(payload)
>>> p2
<Point: x=10, y=3>
Models are mainly used for describing the data in messages: both keys and
values can be described as models.
"""
import abc
import warnings
from datetime import datetime
from functools import partial
from typing import (
Any,
Callable,
ClassVar,
Iterable,
List,
MutableMapping,
Optional,
Tuple,
Type,
)
from mode.utils.objects import canoname
from faust.exceptions import ValidationError
from faust.serializers.codecs import CodecArg, dumps, loads
from faust.types.models import (
CoercionMapping,
FieldDescriptorT,
FieldMap,
ModelOptions,
ModelT,
)
__all__ = ['Model', 'maybe_model', 'registry']
# NOTES:
# - Records are described in the same notation as named tuples in Python 3.6.
# To accomplish this ``__init_subclass__`` defined in :pep:`487` is used.
#
# When accessed on the Record class, the attributes are actually field
# descriptors that return information about the field:
# >>> Point.x
# <FieldDescriptor: Point.x: int>
#
# This field descriptor holds information about the name of the field, the
# value type of the field, and also what Record subclass it belongs to.
#
# - Sometimes field descriptions are passed around as arguments to functions.
#
# - A stream of deposits may be joined with a stream of orders if
# both have an ``account`` field. Field descriptors are used to
# specify the field.
#
# - order_instance.account is data
# (it holds the string account for this particular order).
#
# - order_instance.__class__.account is the field descriptor for the field,
# it's not data but metadata that enables introspection, and it can be
# passed around to describe a field we want to extract or similar.
#
# - FieldDescriptors are Python descriptors: In Python object
# attributes can override what happens when they are get/set/deleted:
#
# class MyDescriptor:
#
# def __get__(self, instance, cls):
# if instance is None:
# print('ACCESS ON CLASS ATTRIBUTE')
# return self
# print('ACCESS ON INSTANCE')
# return 42
#
# class Example:
# foo = MyDescriptor()
#
# The above descriptor overrides __get__, which is called when the attribute
# is accessed (a descriptor may also override __set__ and __del__).
#
#
# You can see the difference in what happens when you access the attribute
# on the class, vs. the instance:
# >>> Example.foo
# ACCESS ON CLASS ATTRIBUTE
# <__main__.MyDescriptor at 0x1049caac8>
#
# >>> x = Example()
# >>> x.foo
# ACCESS ON INSTANCE
# 42
E_ABSTRACT_INSTANCE = '''
Cannot instantiate abstract model.
If this model is used as the field of another model,
and you meant to define a polymorphic relationship: make sure
your abstract model class has the `polymorphic_fields` option enabled:
class {name}(faust.Record, abstract=True, polymorphic_fields=True):
...
'''
#: Global map of namespace -> Model, used to find model classes by name.
#: Every single model defined is added here automatically when a model
#: class is defined.
registry: MutableMapping[str, Type[ModelT]] = {}
[docs]def maybe_model(arg: Any) -> Any:
"""Convert argument to model if possible."""
try:
model = registry[arg['__faust']['ns']]
except (KeyError, TypeError):
return arg
else:
return model.from_data(arg)
[docs]class Model(ModelT):
"""Meta description model for serialization."""
#: Set to True if this is an abstract base class.
__is_abstract__: ClassVar[bool] = True
__validation_errors__ = None
_pending_finalizers: ClassVar[Optional[List[Callable]]] = None
#: Serialized data may contain a "blessed key" that mandates
#: how the data should be deserialized. This probably only
#: applies to records, but we need to support it at Model level.
#: The blessed key has a dictionary value with a ``ns`` key:
#: data = {.., '__faust': {'ns': 'examples.simple.Withdrawal'}}
#: When ``Model._maybe_reconstruct` sees this key it will look
#: up that namespace in the :data:`registry`, and if it exists
#: select it as the target model to use for serialization.
#:
#: Is this similar to how unsafe deserialization in pickle/yaml/etc.
#: works? No! pickle/pyyaml allow for arbitrary types to be
#: deserialized (and worse in pickle's case), whereas the blessed
#: key can only deserialize to a hardcoded list of types that are
#: already under the remote control of messages anyway.
#: For example it's not possible to perform remote code execution
#: by providing a blessed key namespace of "os.system", simply
#: because os.system is not in the registry of allowed types.
_blessed_key = '__faust'
@classmethod
def _maybe_namespace(
cls, data: Any,
*,
preferred_type: Type[ModelT] = None,
fast_types: Tuple[Type, ...] = (bytes, str),
isinstance: Callable = isinstance) -> Optional[Type[ModelT]]:
# The serialized data may contain a ``__faust`` blessed key
# holding the name of the model it should be deserialized as.
# So even if value_type=MyModel, the data may mandata that it
# should be deserialized using "foo.bar.baz" instead.
# This is how we deal with Kafka's lack of message headers,
# as needed by the RPC mechanism, without wrapping all data.
if data is None or isinstance(data, fast_types):
return None
try:
ns = data[cls._blessed_key]['ns']
except (KeyError, TypeError):
pass
else:
# we only allow blessed keys when type=None, or type=Model
type_is_abstract = (preferred_type is None or
preferred_type is ModelT or
preferred_type is Model)
try:
model = registry[ns]
except KeyError:
if type_is_abstract:
raise
return None
else:
if (type_is_abstract or
model._options.allow_blessed_key or
model._options.polymorphic_fields):
return model
return None
@classmethod
def _maybe_reconstruct(cls, data: Any) -> Any:
model = cls._maybe_namespace(data)
return model.from_data(data) if model else data
[docs] @classmethod
def loads(cls, s: bytes, *,
default_serializer: CodecArg = None, # XXX use serializer
serializer: CodecArg = None) -> ModelT:
"""Deserialize model object from bytes.
Keyword Arguments:
serializer (CodecArg): Default serializer to use
if no custom serializer was set for this model subclass.
"""
if default_serializer is not None:
warnings.warn(DeprecationWarning(
'default_serializer deprecated, use: serializer'))
ser = cls._options.serializer or serializer or default_serializer
data = loads(ser, s)
return cls.from_data(data)
def __init_subclass__(cls,
serializer: str = None,
namespace: str = None,
include_metadata: bool = None,
isodates: bool = None,
abstract: bool = False,
allow_blessed_key: bool = None,
decimals: bool = None,
coerce: bool = None,
coercions: CoercionMapping = None,
polymorphic_fields: bool = None,
validation: bool = None,
date_parser: Callable[[Any], datetime] = None,
lazy_creation: bool = False,
**kwargs: Any) -> None:
# Python 3.6 added the new __init_subclass__ function that
# makes it possible to initialize subclasses without using
# metaclasses (:pep:`487`).
super().__init_subclass__(**kwargs)
# mypy does not recognize `__init_subclass__` as a classmethod
# and thinks we're mutating a ClassVar when setting:
# cls.__is_abstract__ = False
# To fix this we simply delegate to a _init_subclass classmethod.
finalizer = partial(
cls._init_subclass,
serializer,
namespace,
include_metadata,
isodates,
abstract,
allow_blessed_key,
decimals,
coerce,
coercions,
polymorphic_fields,
validation,
date_parser,
)
if lazy_creation:
cls._pending_finalizers = [finalizer]
else:
cls._pending_finalizers = None
finalizer()
[docs] @classmethod
def make_final(cls) -> None:
pending, cls._pending_finalizers = cls._pending_finalizers, None
if pending:
for finalizer in pending:
finalizer()
@classmethod
def _init_subclass(cls,
serializer: str = None,
namespace: str = None,
include_metadata: bool = None,
isodates: bool = None,
abstract: bool = False,
allow_blessed_key: bool = None,
decimals: bool = None,
coerce: bool = None,
coercions: CoercionMapping = None,
polymorphic_fields: bool = None,
validation: bool = None,
date_parser: Callable[[Any], datetime] = None) -> None:
# Can set serializer/namespace/etc. using:
# class X(Record, serializer='json', namespace='com.vandelay.X'):
# ...
try:
custom_options = cls.Options
except AttributeError:
custom_options = None
else:
delattr(cls, 'Options')
options = getattr(cls, '_options', None)
if options is None:
options = ModelOptions()
options.coercions = {}
options.defaults = {}
else:
options = options.clone_defaults()
if custom_options:
options.__dict__.update(custom_options.__dict__)
if coerce is not None:
options.coerce = coerce
if coercions is not None:
options.coercions.update(coercions)
if serializer is not None:
options.serializer = serializer
if include_metadata is not None:
options.include_metadata = include_metadata
if isodates is not None:
options.isodates = isodates
if decimals is not None:
options.decimals = decimals
if allow_blessed_key is not None:
options.allow_blessed_key = allow_blessed_key
if polymorphic_fields is not None:
options.polymorphic_fields = polymorphic_fields
if validation is not None:
options.validation = validation
options.coerce = True # validation implies coerce
if date_parser is not None:
options.date_parser = date_parser
options.namespace = namespace or canoname(cls)
if abstract:
# Custom base classes can set this to skip class initialization.
cls.__is_abstract__ = True
cls._options = options
cls.__init__ = cls.__abstract_init__ # type: ignore
return
cls.__is_abstract__ = False
# Add introspection capabilities
cls._contribute_to_options(options)
# Add FieldDescriptors for every field.
options.descriptors = cls._contribute_field_descriptors(
cls, options)
# Store options on new subclass.
cls._options = options
cls._contribute_methods()
# Register in the global registry, so we can look up
# models by namespace.
registry[options.namespace] = cls
codegens = [
('__init__', cls._BUILD_init, '_model_init'),
('__hash__', cls._BUILD_hash, '_model_hash'),
('__eq__', cls._BUILD_eq, '_model_eq'),
('__ne__', cls._BUILD_ne, '_model_ne'),
('__gt__', cls._BUILD_gt, '_model_gt'),
('__ge__', cls._BUILD_ge, '_model_ge'),
('__lt__', cls._BUILD_lt, '_model_lt'),
('__le__', cls._BUILD_le, '_model_le'),
]
for meth_name, meth_gen, attr_name in codegens:
# self._model_init = cls._BUILD_init()
# if '__init__' not in cls.__dict__:
# cls.__init__ = self._model_init
meth = meth_gen()
setattr(cls, attr_name, meth)
if meth_name not in cls.__dict__:
setattr(cls, meth_name, meth)
def __abstract_init__(self) -> None:
raise NotImplementedError(E_ABSTRACT_INSTANCE.format(
name=type(self).__name__,
))
@classmethod
@abc.abstractmethod
def _contribute_to_options(
cls, options: ModelOptions) -> None: # pragma: no cover
...
@classmethod
def _contribute_methods(cls) -> None: # pragma: no cover
...
@classmethod
@abc.abstractmethod
def _contribute_field_descriptors(
cls,
target: Type,
options: ModelOptions,
parent: FieldDescriptorT = None) -> FieldMap: # pragma: no cover
...
@classmethod
@abc.abstractmethod
def _BUILD_init(cls) -> Callable[[], None]: # pragma: no cover
...
@classmethod
@abc.abstractmethod
def _BUILD_hash(cls) -> Callable[[], None]: # pragma: no cover
...
@classmethod
@abc.abstractmethod
def _BUILD_eq(cls) -> Callable[[], None]: # pragma: no cover
...
[docs] @abc.abstractmethod
def to_representation(self) -> Any: # pragma: no cover
"""Convert object to JSON serializable object."""
@abc.abstractmethod
def _humanize(self) -> str: # pragma: no cover
"""Return string representation of object for debugging purposes."""
...
[docs] def is_valid(self) -> bool:
return True if not self.validate() else False
[docs] def validate(self) -> List[ValidationError]:
errors = self.__validation_errors__
if errors is None:
errors = self.__validation_errors__ = list(self._itervalidate())
return errors
[docs] def validate_or_raise(self) -> None:
errors = self.validate()
if errors:
raise errors[0]
def _itervalidate(self) -> Iterable[ValidationError]:
for name, descr in self._options.descriptors.items():
yield from descr.validate_all(getattr(self, name))
@property
def validation_errors(self) -> List[ValidationError]:
return self.validate()
[docs] def derive(self, *objects: ModelT, **fields: Any) -> ModelT:
"""Derive new model with certain fields changed."""
return self._derive(*objects, **fields)
@abc.abstractmethod # pragma: no cover
def _derive(self, *objects: ModelT, **fields: Any) -> ModelT:
raise NotImplementedError()
[docs] def dumps(self, *, serializer: CodecArg = None) -> bytes:
"""Serialize object to the target serialization format."""
return dumps(serializer or self._options.serializer,
self.to_representation())
def __repr__(self) -> str:
return f'<{type(self).__name__}: {self._humanize()}>'
