"""
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 typing import Any, Callable, Protocol, Generic, Optional, TYPE_CHECKING
from collections.abc import Iterable
from ...facets.plain import UnitDefinition, PlainQuantity, PlainUnit, MagnitudeT
from ...util import UnitsContainer, to_units_container
from .definitions import ContextDefinition
from ..._typing import Magnitude
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
[docs]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. * 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. * 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: Optional[str] = None,
aliases: tuple[str, ...] = tuple(),
defaults: Optional[dict[str, Any]] = None,
) -> None:
self.name: Optional[str] = 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: Optional[ToBaseFunc] = 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: Optional[ToBaseFunc] = 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
) -> Magnitude:
"""Transform a value."""
_key = self.__keytransform__(src, dst)
func = self.funcs[_key]
return func(registry, value, **self.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[
Optional[str],
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: Optional[dict[SrcDst, set[UnitsContainer]]] = 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: Optional[int] = 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
):
"""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)
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)
