from __future__ import annotations
import copy
import itertools
import weakref
from collections.abc import Generator
from typing import Any, ClassVar, Generic, TypeVar
from mopidy.models.fields import Field
T = TypeVar("T", bound="type")
# Registered models for automatic deserialization
_models = {}
[docs]
class ImmutableObject:
"""Superclass for immutable objects whose fields can only be modified via the
constructor.
This version of this class has been retained to avoid breaking any clients
relying on it's behavior. Internally in Mopidy we now use
:class:`ValidatedImmutableObject` for type safety and it's much smaller
memory footprint.
:param kwargs: kwargs to set as fields on the object
:type kwargs: any
"""
# Any sub-classes that don't set slots won't be effected by the base using
# slots as they will still get an instance dict.
__slots__ = ["__weakref__"]
def __init__(self, *_args, **kwargs):
for key, value in kwargs.items():
if not self._is_valid_field(key):
raise TypeError(
f"__init__() got an unexpected keyword argument {key!r}"
)
self._set_field(key, value)
def __setattr__(self, name, value):
if name.startswith("_"):
object.__setattr__(self, name, value)
else:
raise AttributeError("Object is immutable.")
def __delattr__(self, name):
if name.startswith("_"):
object.__delattr__(self, name)
else:
raise AttributeError("Object is immutable.")
def _is_valid_field(self, name):
return hasattr(self, name) and not callable(getattr(self, name))
def _set_field(self, name, value):
if value == getattr(self.__class__, name):
self.__dict__.pop(name, None)
else:
self.__dict__[name] = value
def _items(self) -> Generator[tuple[str, Any], Any, None]:
yield from self.__dict__.items()
def __repr__(self):
kwarg_pairs = []
for key, value in sorted(self._items()):
if isinstance(value, frozenset | tuple):
if not value:
continue
value = list(value)
kwarg_pairs.append(f"{key}={value!r}")
return f"{self.__class__.__name__}({', '.join(kwarg_pairs)})"
def __hash__(self):
hash_sum = 0
for key, value in self._items():
hash_sum += hash(key) + hash(value)
return hash_sum
def __eq__(self, other):
if not isinstance(other, self.__class__):
return False
return all(
a == b
for a, b in itertools.zip_longest(
self._items(), other._items(), fillvalue=object()
)
)
def __ne__(self, other):
return not self.__eq__(other)
[docs]
def replace(self, **kwargs):
"""Replace the fields in the model and return a new instance.
Examples::
# Returns a track with a new name
Track(name='foo').replace(name='bar')
# Return an album with a new number of tracks
Album(num_tracks=2).replace(num_tracks=5)
:param kwargs: kwargs to set as fields on the object
:type kwargs: any
:rtype: instance of the model with replaced fields
"""
other = copy.copy(self)
for key, value in kwargs.items():
if not self._is_valid_field(key):
raise TypeError(f"replace() got an unexpected keyword argument {key!r}")
other._set_field(key, value)
return other
def serialize(self):
data = {}
data["__model__"] = self.__class__.__name__
for key, value in self._items():
if isinstance(value, set | frozenset | list | tuple):
value = [
v.serialize() if isinstance(v, ImmutableObject) else v
for v in value
]
elif isinstance(value, ImmutableObject):
value = value.serialize()
if not (isinstance(value, list) and len(value) == 0):
data[key] = value
return data
class _ValidatedImmutableObjectMeta(type, Generic[T]):
"""Helper that initializes fields, slots and memoizes instance creation."""
_instances: dict[weakref.ReferenceType[_ValidatedImmutableObjectMeta[T]], T] = {} # noqa: RUF012
def __new__(
cls: type[_ValidatedImmutableObjectMeta],
name: str,
bases: tuple[type, ...],
attrs: dict[str, Any],
) -> _ValidatedImmutableObjectMeta:
fields = {}
for base in bases: # Copy parent fields over to our state
fields.update(getattr(base, "_fields", {}))
for key, value in attrs.items(): # Add our own fields
if isinstance(value, Field):
fields[key] = "_" + key
value._name = key
attrs["_fields"] = fields
attrs["_instances"] = weakref.WeakValueDictionary()
attrs["__slots__"] = list(attrs.get("__slots__", [])) + list(fields.values())
clsc: _ValidatedImmutableObjectMeta = super().__new__(cls, name, bases, attrs)
if clsc.__name__ != "ValidatedImmutableObject":
_models[clsc.__name__] = clsc
return clsc
def __call__(
cls,
*args: Any,
**kwargs: Any,
) -> T:
instance = super().__call__(*args, **kwargs)
return cls._instances.setdefault(weakref.ref(instance), instance)
[docs]
class ValidatedImmutableObject(
ImmutableObject, metaclass=_ValidatedImmutableObjectMeta
):
"""Superclass for immutable objects whose fields can only be modified via the
constructor. Fields should be :class:`Field` instances to ensure type
safety in our models.
Note that since these models can not be changed, we heavily memoize them
to save memory. So constructing a class with the same arguments twice will
give you the same instance twice.
"""
_fields: ClassVar[dict[str, Any]]
_instances: ClassVar[weakref.WeakValueDictionary]
__slots__ = ["_hash"]
def __hash__(self):
if not hasattr(self, "_hash"):
hash_sum = super().__hash__()
object.__setattr__(self, "_hash", hash_sum)
return self._hash
def _is_valid_field(self, name):
return name in self._fields
def _set_field(self, name, value):
object.__setattr__(self, name, value)
def _items(self) -> Generator[tuple[str, Any], Any, None]:
for field, key in self._fields.items():
if hasattr(self, key):
yield field, getattr(self, key)
[docs]
def replace(self, **kwargs):
"""Replace the fields in the model and return a new instance.
Examples::
# Returns a track with a new name
Track(name='foo').replace(name='bar')
# Return an album with a new number of tracks
Album(num_tracks=2).replace(num_tracks=5)
Note that internally we memoize heavily to keep memory usage down given
our overly repetitive data structures. So you might get an existing
instance if it contains the same values.
:param kwargs: kwargs to set as fields on the object
:type kwargs: any
:rtype: instance of the model with replaced fields
"""
if not kwargs:
return self
other = super().replace(**kwargs)
if hasattr(self, "_hash"):
object.__delattr__(other, "_hash")
return self._instances.setdefault(weakref.ref(other), other)