Skip to main content
`Ctrl`+`K`

#

# Source code for pint.facets.context.objects

    """
    pint.facets.context.objects
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~

    :copyright: 2022 by Pint Authors, see AUTHORS for more details.
    :license: BSD, see LICENSE for more details.
    """

    from __future__ import annotations

    import weakref
    from collections import ChainMap, defaultdict
    from collections.abc import Callable, Iterable
    from typing import TYPE_CHECKING, Any, Generic, Protocol

    from ..._typing import Magnitude
    from ...facets.plain import MagnitudeT, PlainQuantity, PlainUnit, UnitDefinition
    from ...util import UnitsContainer, to_units_container
    from .definitions import ContextDefinition

    if TYPE_CHECKING:
        from ...registry import UnitRegistry

    class Transformation(Protocol):
        def __call__(
            self, ureg: UnitRegistry, value: PlainQuantity, **kwargs: Any
        ) -> PlainQuantity: ...

    from ..._typing import UnitLike

    ToBaseFunc = Callable[[UnitsContainer], UnitsContainer]
    SrcDst = tuple[UnitsContainer, UnitsContainer]

    class ContextQuantity(Generic[MagnitudeT], PlainQuantity[MagnitudeT]):
        pass

    class ContextUnit(PlainUnit):
        pass

    class Context:
        """A specialized container that defines transformation functions from one
        dimension to another. Each Dimension are specified using a UnitsContainer.
        Simple transformation are given with a function taking a single parameter.

        Conversion functions may take optional keyword arguments and the context
        can have default values for these arguments.

        Additionally, a context may host redefinitions.

        A redefinition must be performed among units that already exist in the registry. It
        cannot change the dimensionality of a unit. The symbol and aliases are automatically
        inherited from the registry.

        See ContextDefinition for the definition file syntax.

        Parameters
        ----------
        name : str or None, optional
            Name of the context (must be unique within the registry).
            Use None for anonymous Context. (Default value = None).
        aliases : iterable of str
            Other names for the context.
        defaults : None or dict
            Maps variable names to values.

        Example
        -------

        >>> from pint.util import UnitsContainer
        >>> from pint import Context, UnitRegistry
        >>> ureg = UnitRegistry()
        >>> timedim = UnitsContainer({"[time]": 1})
        >>> spacedim = UnitsContainer({"[length]": 1})
        >>> def time_to_len(ureg, time):
        ...     "Time to length converter"
        ...     return 3.0 * time
        >>> c = Context()
        >>> c.add_transformation(timedim, spacedim, time_to_len)
        >>> c.transform(timedim, spacedim, ureg, 2)
        6.0
        >>> def time_to_len_indexed(ureg, time, n=1):
        ...     "Time to length converter, n is the index of refraction of the material"
        ...     return 3.0 * time / n
        >>> c = Context(defaults={"n": 3})
        >>> c.add_transformation(timedim, spacedim, time_to_len_indexed)
        >>> c.transform(timedim, spacedim, ureg, 2)
        2.0
        >>> c.redefine("pound = 0.5 kg")
        """

        def __init__(
            self,
            name: str | None = None,
            aliases: tuple[str, ...] = tuple(),
            defaults: dict[str, Any] | None = None,
        ) -> None:
            self.name: str | None = name
            self.aliases: tuple[str, ...] = aliases

            #: Maps (src, dst) -> transformation function
            self.funcs: dict[SrcDst, Transformation] = {}

            #: Maps defaults variable names to values
            self.defaults: dict[str, Any] = defaults or {}

            # Store Definition objects that are context-specific
            # TODO: narrow type this if possible.
            self.redefinitions: list[Any] = []

            # Flag set to True by the Registry the first time the context is enabled
            self.checked = False

            #: Maps (src, dst) -> self
            #: Used as a convenience dictionary to be composed by ContextChain
            self.relation_to_context: weakref.WeakValueDictionary[SrcDst, Context] = (
                weakref.WeakValueDictionary()
            )

        @classmethod
        def from_context(cls, context: Context, **defaults: Any) -> Context:
            """Creates a new context that shares the funcs dictionary with the
            original context. The default values are copied from the original
            context and updated with the new defaults.

            If defaults is empty, return the same context.

            Parameters
            ----------
            context : pint.Context
                Original context.
            **defaults

            Returns
            -------
            pint.Context
            """
            if defaults:
                newdef = dict(context.defaults, **defaults)
                c = cls(context.name, context.aliases, newdef)
                c.funcs = context.funcs
                c.redefinitions = context.redefinitions
                for edge in context.funcs:
                    c.relation_to_context[edge] = c
                return c
            return context

        @classmethod
        def from_lines(
            cls,
            lines: Iterable[str],
            to_base_func: ToBaseFunc | None = None,
            non_int_type: type = float,
        ) -> Context:
            context_definition = ContextDefinition.from_lines(lines, non_int_type)

            if context_definition is None:
                raise ValueError(f"Could not define Context from from {lines}")

            return cls.from_definition(context_definition, to_base_func)

        @classmethod
        def from_definition(
            cls, cd: ContextDefinition, to_base_func: ToBaseFunc | None = None
        ) -> Context:
            ctx = cls(cd.name, cd.aliases, cd.defaults)

            for definition in cd.redefinitions:
                ctx._redefine(definition)

            for relation in cd.relations:
                try:
                    # TODO: check to_base_func. Is it a good API idea?
                    if to_base_func:
                        src = to_base_func(relation.src)
                        dst = to_base_func(relation.dst)
                    else:
                        src, dst = relation.src, relation.dst
                    ctx.add_transformation(src, dst, relation.transformation)
                    if relation.bidirectional:
                        ctx.add_transformation(dst, src, relation.transformation)
                except Exception as exc:
                    raise ValueError(
                        f"Could not add Context {cd.name} relation {relation}"
                    ) from exc

            return ctx

        def add_transformation(
            self, src: UnitLike, dst: UnitLike, func: Transformation
        ) -> None:
            """Add a transformation function to the context."""

            _key = self.__keytransform__(src, dst)
            self.funcs[_key] = func
            self.relation_to_context[_key] = self

        def remove_transformation(self, src: UnitLike, dst: UnitLike) -> None:
            """Add a transformation function to the context."""

            _key = self.__keytransform__(src, dst)
            del self.funcs[_key]
            del self.relation_to_context[_key]

        @staticmethod
        def __keytransform__(src: UnitLike, dst: UnitLike) -> SrcDst:
            return to_units_container(src), to_units_container(dst)

        def transform(
            self,
            src: UnitLike,
            dst: UnitLike,
            registry: Any,
            value: Magnitude,
            **ctx_kwargs,
        ) -> Magnitude:
            """Transform a value."""

            _key = self.__keytransform__(src, dst)
            func = self.funcs[_key]
            defaults = self.defaults.copy()
            defaults.update(ctx_kwargs)
            return func(registry, value, **defaults)

        def redefine(self, definition: str) -> None:
            """Override the definition of a unit in the registry.

            Parameters
            ----------
            definition : str
                <unit> = <new definition>``, e.g. ``pound = 0.5 kg``
            """
            from ...delegates import ParserConfig, txt_defparser

            # TODO: kept for backwards compatibility.
            #       this is not a good idea as we have no way of known the correct non_int_type
            cfg = ParserConfig(float)
            parser = txt_defparser.DefParser(cfg, None)
            pp = parser.parse_string(definition)
            for definition in parser.iter_parsed_project(pp):
                if isinstance(definition, UnitDefinition):
                    self._redefine(definition)

        def _redefine(self, definition: UnitDefinition):
            self.redefinitions.append(definition)

        def hashable(
            self,
        ) -> tuple[
            str | None,
            tuple[str, ...],
            frozenset[tuple[SrcDst, int]],
            frozenset[tuple[str, Any]],
            tuple[Any, ...],
        ]:
            """Generate a unique hashable and comparable representation of self, which can
            be used as a key in a dict. This class cannot define ``__hash__`` because it is
            mutable, and the Python interpreter does cache the output of ``__hash__``.

            Returns
            -------
            tuple
            """
            return (
                self.name,
                tuple(self.aliases),
                frozenset((k, id(v)) for k, v in self.funcs.items()),
                frozenset(self.defaults.items()),
                tuple(self.redefinitions),
            )

    class ContextChain(ChainMap[SrcDst, Context]):
        """A specialized ChainMap for contexts that simplifies finding rules
        to transform from one dimension to another.
        """

        def __init__(self):
            super().__init__()
            self.contexts: list[Context] = []
            self.maps.clear()  # Remove default empty map
            self._graph: dict[SrcDst, set[UnitsContainer]] | None = None

        def insert_contexts(self, *contexts: Context):
            """Insert one or more contexts in reversed order the chained map.
            (A rule in last context will take precedence)

            To facilitate the identification of the context with the matching rule,
            the *relation_to_context* dictionary of the context is used.
            """

            self.contexts = list(reversed(contexts)) + self.contexts
            self.maps = [ctx.relation_to_context for ctx in reversed(contexts)] + self.maps
            self._graph = None

        def remove_contexts(self, n: int | None = None):
            """Remove the last n inserted contexts from the chain.

            Parameters
            ----------
            n: int
                (Default value = None)
            """

            del self.contexts[:n]
            del self.maps[:n]
            self._graph = None

        @property
        def defaults(self) -> dict[str, Any]:
            for ctx in self.values():
                return ctx.defaults
            return {}

        @property
        def graph(self):
            """The graph relating"""
            if self._graph is None:
                self._graph = defaultdict(set)
                for fr_, to_ in self:
                    self._graph[fr_].add(to_)
            return self._graph

        # TODO: type registry
        def transform(
            self,
            src: UnitsContainer,
            dst: UnitsContainer,
            registry: Any,
            value: Magnitude,
            **ctx_kwargs,
        ):
            """Transform the value, finding the rule in the chained context.
            (A rule in last context will take precedence)
            """
            return self[(src, dst)].transform(src, dst, registry, value, **ctx_kwargs)

        def hashable(self) -> tuple[Any, ...]:
            """Generate a unique hashable and comparable representation of self, which can
            be used as a key in a dict. This class cannot define ``__hash__`` because it is
            mutable, and the Python interpreter does cache the output of ``__hash__``.
            """
            return tuple(ctx.hashable() for ctx in self.contexts)