Source code for pennylane.data.base.mapper

# Copyright 2018-2023 Xanadu Quantum Technologies Inc.

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Contains a class for mapping HDF5 groups to Dataset Attributes, and a mixin
class that provides the mapper class."""


from collections.abc import Iterator, Mapping, MutableMapping
from types import MappingProxyType
from typing import Any, Optional, Type

from pennylane.data.base.attribute import (
    AttributeInfo,
    DatasetAttribute,
    get_attribute_type,
    match_obj_type,
)
from pennylane.data.base.hdf5 import HDF5Any, HDF5Group


class DatasetNotWriteableError(RuntimeError):
    """Exception raised when attempting to set an attribute
    on a dataset whose underlying file is not writeable."""

    def __init__(self, bind: HDF5Any):
        self.bind = bind

        super().__init__(f"Dataset file is not writeable: {bind.filename}")


class AttributeTypeMapper(MutableMapping):
    """
    This class performs the mapping between the objects contained
    in a HDF5 group and Dataset attributes.
    """

    bind: HDF5Group
    _cache: dict[str, DatasetAttribute]

    def __init__(self, bind: HDF5Group) -> None:
        self._cache = {}
        self.bind = bind

    def __getitem__(self, key: str) -> DatasetAttribute:
        if key in self._cache:
            return self._cache[key]

        h5_obj = self.bind[key]

        attr_type = get_attribute_type(h5_obj)
        attr = attr_type(bind=h5_obj)
        self._cache[key] = attr

        return attr

    @property
    def info(self) -> AttributeInfo:
        """Return ``AttributeInfo`` for ``self.bind``."""
        return AttributeInfo(self.bind.attrs)

    def set_item(
        self,
        key: str,
        value: Any,
        info: Optional[AttributeInfo],
        require_type: Optional[Type[DatasetAttribute]] = None,
    ) -> None:
        """Creates or replaces attribute ``key`` with ``value``, optionally
        including ``info``.

        Args:
            key: Name of attribute in HDF5 group
            value: Attribute value, either a compatible object or an already
                initialized ``DatasetAttribute``.
            info: Extra info to attach to attribute
            require_type: Force the ``value`` to be serialized as this type.
                If ``value`` is an ``DatasetAttribute``, it must be an instance of ``require_type``.
                Otherwise, ``value`` must be serializable by ``require_type``.
        """
        try:
            if isinstance(value, DatasetAttribute):
                if require_type and not isinstance(value, require_type):
                    raise TypeError(
                        f"Expected '{key}' to be of type '{require_type.__name__}', but got '{type(value).__name__}'."
                    )

                value._set_parent(self.bind, key)  # pylint: disable=protected-access
                if info:
                    info.save(value.info)

            elif require_type is not None:
                require_type(value, info, parent_and_key=(self.bind, key))
            else:
                attr_type = match_obj_type(value)
                attr_type(value, info, parent_and_key=(self.bind, key))
        except ValueError as exc:
            if exc.args[0] == "Unable to create dataset (no write intent on file)":
                raise DatasetNotWriteableError(self.bind) from exc

            raise exc

        self._cache.pop(key, None)

    def __setitem__(self, key: str, value: Any) -> None:
        self.set_item(key, value, None)

    def move(self, src: str, dest: str) -> None:
        """Moves the attribute stored at ``src`` in ``bind`` to ``dest``."""
        self.bind.move(src, dest)
        self._cache.pop(src, None)

    def view(self) -> Mapping[str, DatasetAttribute]:
        """Returns a read-only mapping of the attributes in ``bind``."""
        return MappingProxyType(self)

    def __len__(self) -> int:
        return len(self.bind)

    def __iter__(self) -> Iterator[str]:
        return iter(self.bind)

    def __contains__(self, key: str) -> bool:
        return key in self._cache or key in self.bind

    def __delitem__(self, key: str) -> None:
        self._cache.pop(key, None)
        del self.bind[key]

    def __repr__(self):
        return repr(dict(self))

    def __str__(self):
        return str(dict(self))


class MapperMixin:  # pylint: disable=too-few-public-methods
    """Mixin class for Dataset types that provide an interface
    to a HDF5 group, e.g `DatasetList`, `DatasetDict`. Provides
    a `_mapper` property over the type's ``bind`` attribute."""

    bind: HDF5Group

    __mapper: AttributeTypeMapper = None

    @property
    def _mapper(self) -> AttributeTypeMapper:
        if self.__mapper is None:
            self.__mapper = AttributeTypeMapper(self.bind)

        return self.__mapper

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