Source code for pennylane.configuration

# Copyright 2018-2021 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.
r"""
This module contains the :class:`Configuration` class, which is used to
load, store, save, and modify configuration options for PennyLane and all
supported plugins and devices.
"""

import contextlib
import os

import tomlkit as toml
from appdirs import user_config_dir


class Configuration:
    """Configuration class.

    This class is responsible for loading, saving, and storing PennyLane
    and plugin/device configurations.

    Args:
        name (str): filename of the configuration file.
            This should be a valid TOML file. You may also pass an absolute
            or a relative file path to the configuration file.
    """

    def __init__(self, name):
        # Look for an existing configuration file
        self._config = {}
        self._filepath = None
        self._name = name
        self._user_config_dir = user_config_dir("pennylane", "Xanadu")
        self._env_config_dir = os.environ.get("PENNYLANE_CONF", "")

        # search the current directory the directory under environment
        # variable PENNYLANE_CONF, and default user config directory, in that order.
        directories = [os.curdir, self._env_config_dir, self._user_config_dir, ""]
        for directory in directories:
            with contextlib.suppress(FileNotFoundError):
                self._filepath = os.path.join(directory, self._name)
                self.load(self._filepath)
                break

    def __str__(self):
        if self._config:
            return f"{self._config}"
        return ""

    def __repr__(self):
        return f"PennyLane Configuration <{self._filepath}>"

    @property
    def path(self):
        """Return the path of the loaded configuration file.

        Returns:
            str: If no configuration is loaded, this returns ``None``."""
        return self._filepath

    def load(self, filepath):
        """Load a configuration file.

        Args:
            filepath (str): path to the configuration file.
        """
        with open(filepath, "r", encoding="utf8") as f:
            self._config = toml.load(f)

    def save(self, filepath):
        """Save a configuration file.

        Args:
            filepath (str): path to the configuration file.
        """
        with open(filepath, "w", encoding="utf8") as f:
            toml.dump(self._config, f)

    def __getitem__(self, key):
        keys = key.split(".")
        return self.safe_get(self._config, *keys)

    def __setitem__(self, key, value):
        keys = key.split(".")
        self.safe_set(self._config, value, *keys)

    def __bool__(self):
        return bool(self._config)

    @staticmethod
    def safe_set(dct, value, *keys):
        """Safely set the value of a key from a nested dictionary.

        If any key provided does not exist, a dictionary containing the
        remaining keys is dynamically created and set to the required value.

        Args:
            dct (dict): the dictionary to set the value of.
            value: the value to set. Can be any valid type.
            *keys: each additional argument corresponds to a nested key.
        """
        for key in keys[:-1]:
            dct = dct.setdefault(key, {})

        dct[keys[-1]] = value

    @staticmethod
    def safe_get(dct, *keys):
        """Safely return value from a nested dictionary.

        If any key provided does not exist, an empty dictionary is returned.

        Args:
            dct (dict): the dictionary to set the value of.
            *keys: each additional argument corresponds to a nested key.

        Returns:
            value corresponding to ``dct[keys[0]][keys[1]]`` etc.
        """
        for key in keys:
            try:
                dct = dct[key]
            except KeyError:
                return {}
        return dct

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