""" Physical quantities. """ from sympy import AtomicExpr, Symbol, sympify from sympy.physics.units.dimensions import _QuantityMapper from sympy.physics.units.prefixes import Prefix from sympy.utilities.exceptions import SymPyDeprecationWarning class Quantity(AtomicExpr): """ Physical quantity: can be a unit of measure, a constant or a generic quantity. """ is_commutative = True is_real = True is_number = False is_nonzero = True _diff_wrt = True def __new__(cls, name, abbrev=None, dimension=None, scale_factor=None, latex_repr=None, pretty_unicode_repr=None, pretty_ascii_repr=None, mathml_presentation_repr=None, **assumptions): if not isinstance(name, Symbol): name = Symbol(name) # For Quantity(name, dim, scale, abbrev) to work like in the # old version of Sympy: if not isinstance(abbrev, str) and not \ isinstance(abbrev, Symbol): dimension, scale_factor, abbrev = abbrev, dimension, scale_factor if dimension is not None: SymPyDeprecationWarning( deprecated_since_version="1.3", issue=14319, feature="Quantity arguments", useinstead="unit_system.set_quantity_dimension_map", ).warn() if scale_factor is not None: SymPyDeprecationWarning( deprecated_since_version="1.3", issue=14319, feature="Quantity arguments", useinstead="SI_quantity_scale_factors", ).warn() if abbrev is None: abbrev = name elif isinstance(abbrev, str): abbrev = Symbol(abbrev) obj = AtomicExpr.__new__(cls, name, abbrev) obj._name = name obj._abbrev = abbrev obj._latex_repr = latex_repr obj._unicode_repr = pretty_unicode_repr obj._ascii_repr = pretty_ascii_repr obj._mathml_repr = mathml_presentation_repr if dimension is not None: # TODO: remove after deprecation: obj.set_dimension(dimension) if scale_factor is not None: # TODO: remove after deprecation: obj.set_scale_factor(scale_factor) return obj def set_dimension(self, dimension, unit_system="SI"): SymPyDeprecationWarning( deprecated_since_version="1.5", issue=17765, feature="Moving method to UnitSystem class", useinstead="unit_system.set_quantity_dimension or {}.set_global_relative_scale_factor".format(self), ).warn() from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_unit_system(unit_system) unit_system.set_quantity_dimension(self, dimension) def set_scale_factor(self, scale_factor, unit_system="SI"): SymPyDeprecationWarning( deprecated_since_version="1.5", issue=17765, feature="Moving method to UnitSystem class", useinstead="unit_system.set_quantity_scale_factor or {}.set_global_relative_scale_factor".format(self), ).warn() from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_unit_system(unit_system) unit_system.set_quantity_scale_factor(self, scale_factor) def set_global_dimension(self, dimension): _QuantityMapper._quantity_dimension_global[self] = dimension def set_global_relative_scale_factor(self, scale_factor, reference_quantity): """ Setting a scale factor that is valid across all unit system. """ from sympy.physics.units import UnitSystem scale_factor = sympify(scale_factor) # replace all prefixes by their ratio to canonical units: scale_factor = scale_factor.replace( lambda x: isinstance(x, Prefix), lambda x: x.scale_factor ) scale_factor = sympify(scale_factor) UnitSystem._quantity_scale_factors_global[self] = (scale_factor, reference_quantity) UnitSystem._quantity_dimensional_equivalence_map_global[self] = reference_quantity @property def name(self): return self._name @property def dimension(self): from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_default_unit_system() return unit_system.get_quantity_dimension(self) @property def abbrev(self): """ Symbol representing the unit name. Prepend the abbreviation with the prefix symbol if it is defines. """ return self._abbrev @property def scale_factor(self): """ Overall magnitude of the quantity as compared to the canonical units. """ from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_default_unit_system() return unit_system.get_quantity_scale_factor(self) def _eval_is_positive(self): return True def _eval_is_constant(self): return True def _eval_Abs(self): return self def _eval_subs(self, old, new): if isinstance(new, Quantity) and self != old: return self @staticmethod def get_dimensional_expr(expr, unit_system="SI"): SymPyDeprecationWarning( deprecated_since_version="1.5", issue=17765, feature="get_dimensional_expr() is now associated with UnitSystem objects. " \ "The dimensional relations depend on the unit system used.", useinstead="unit_system.get_dimensional_expr" ).warn() from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_unit_system(unit_system) return unit_system.get_dimensional_expr(expr) @staticmethod def _collect_factor_and_dimension(expr, unit_system="SI"): """Return tuple with scale factor expression and dimension expression.""" SymPyDeprecationWarning( deprecated_since_version="1.5", issue=17765, feature="This method has been moved to the UnitSystem class.", useinstead="unit_system._collect_factor_and_dimension", ).warn() from sympy.physics.units import UnitSystem unit_system = UnitSystem.get_unit_system(unit_system) return unit_system._collect_factor_and_dimension(expr) def _latex(self, printer): if self._latex_repr: return self._latex_repr else: return r'\text{{{}}}'.format(self.args[1] \ if len(self.args) >= 2 else self.args[0]) def convert_to(self, other, unit_system="SI"): """ Convert the quantity to another quantity of same dimensions. Examples ======== >>> from sympy.physics.units import speed_of_light, meter, second >>> speed_of_light speed_of_light >>> speed_of_light.convert_to(meter/second) 299792458*meter/second >>> from sympy.physics.units import liter >>> liter.convert_to(meter**3) meter**3/1000 """ from .util import convert_to return convert_to(self, other, unit_system) @property def free_symbols(self): """Return free symbols from quantity.""" return set()