# -*- coding: utf-8 -*- """ pint.context ~~~~~~~~~~~~ Functions and classes related to context definitions and application. :copyright: 2016 by Pint Authors, see AUTHORS for more details.. :license: BSD, see LICENSE for more details. """ import re import weakref from collections import ChainMap, defaultdict from .util import (ParserHelper, UnitsContainer, to_units_container, SourceIterator) from .errors import DefinitionSyntaxError #: Regex to match the header parts of a context. _header_re = re.compile('@context\s*(?P\(.*\))?\s+(?P\w+)\s*(=(?P.*))*') #: Regex to match variable names in an equation. _varname_re = re.compile('[A-Za-z_][A-Za-z0-9_]*') def _expression_to_function(eq): def func(ureg, value, **kwargs): return ureg.parse_expression(eq, value=value, **kwargs) return func 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. >>> timedim = UnitsContainer({'[time]': 1}) >>> spacedim = UnitsContainer({'[length]': 1}) >>> def f(time): ... 'Time to length converter' ... return 3. * time >>> c = Context() >>> c.add_transformation(timedim, spacedim, f) >>> c.transform(timedim, spacedim, 2) 6 Conversion functions may take optional keyword arguments and the context can have default values for these arguments. >>> def f(time, n): ... 'Time to length converter, n is the index of refraction of the material' ... return 3. * time / n >>> c = Context(n=3) >>> c.add_transformation(timedim, spacedim, f) >>> c.transform(timedim, spacedim, 2) 2 """ def __init__(self, name=None, aliases=(), defaults=None): self.name = name self.aliases = aliases #: Maps (src, dst) -> transformation function self.funcs = {} #: Maps defaults variable names to values self.defaults = defaults or {} #: Maps (src, dst) -> self #: Used as a convenience dictionary to be composed by ContextChain self.relation_to_context = weakref.WeakValueDictionary() @classmethod def from_context(cls, context, **defaults): """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. """ if defaults: newdef = dict(context.defaults, **defaults) c = cls(context.name, context.aliases, newdef) c.funcs = context.funcs for edge in context.funcs.keys(): c.relation_to_context[edge] = c return c return context @classmethod def from_lines(cls, lines, to_base_func=None): lines = SourceIterator(lines) lineno, header = next(lines) try: r = _header_re.search(header) name = r.groupdict()['name'].strip() aliases = r.groupdict()['aliases'] if aliases: aliases = tuple(a.strip() for a in r.groupdict()['aliases'].split('=')) else: aliases = () defaults = r.groupdict()['defaults'] except: raise DefinitionSyntaxError("Could not parse the Context header '%s'" % header, lineno=lineno) if defaults: def to_num(val): val = complex(val) if not val.imag: return val.real return val _txt = defaults try: defaults = (part.split('=') for part in defaults.strip('()').split(',')) defaults = dict((str(k).strip(), to_num(v)) for k, v in defaults) except (ValueError, TypeError): raise DefinitionSyntaxError("Could not parse Context definition defaults: '%s'" % _txt, lineno=lineno) ctx = cls(name, aliases, defaults) else: ctx = cls(name, aliases) names = set() for lineno, line in lines: try: rel, eq = line.split(':') names.update(_varname_re.findall(eq)) func = _expression_to_function(eq) if '<->' in rel: src, dst = (ParserHelper.from_string(s) for s in rel.split('<->')) if to_base_func: src = to_base_func(src) dst = to_base_func(dst) ctx.add_transformation(src, dst, func) ctx.add_transformation(dst, src, func) elif '->' in rel: src, dst = (ParserHelper.from_string(s) for s in rel.split('->')) if to_base_func: src = to_base_func(src) dst = to_base_func(dst) ctx.add_transformation(src, dst, func) else: raise Exception except: raise DefinitionSyntaxError("Could not parse Context %s relation '%s'" % (name, line), lineno=lineno) if defaults: missing_pars = set(defaults.keys()).difference(set(names)) if missing_pars: raise DefinitionSyntaxError('Context parameters {} not found in any equation.'.format(missing_pars)) return ctx def add_transformation(self, src, dst, func): """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, dst): """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, dst): return to_units_container(src), to_units_container(dst) def transform(self, src, dst, registry, value): """Transform a value. """ _key = self.__keytransform__(src, dst) return self.funcs[_key](registry, value, **self.defaults) class ContextChain(ChainMap): """A specialized ChainMap for contexts that simplifies finding rules to transform from one dimension to another. """ def __init__(self, *args, **kwargs): super(ContextChain, self).__init__(*args, **kwargs) self._graph = None self._contexts = [] def insert_contexts(self, *contexts): """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.insert(0, contexts) self.maps = [ctx.relation_to_context for ctx in reversed(contexts)] + self.maps self._graph = None def remove_contexts(self, n): """Remove the last n inserted contexts from the chain. """ self._contexts = self._contexts[n:] self.maps = self.maps[n:] self._graph = None @property def defaults(self): if self: return list(self.maps[0].values())[0].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 def transform(self, src, dst, registry, value): """Transform the value, finding the rule in the chained context. (A rule in last context will take precedence) :raises: KeyError if the rule is not found. """ return self[(src, dst)].transform(src, dst, registry, value)