| """ |
| Physical quantities. |
| """ |
|
|
| from sympy.core.expr import AtomicExpr |
| from sympy.core.symbol import Symbol |
| from sympy.core.sympify import sympify |
| from sympy.physics.units.dimensions import _QuantityMapper |
| from sympy.physics.units.prefixes import Prefix |
|
|
|
|
| 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 |
| is_physical_constant = False |
| _diff_wrt = True |
|
|
| def __new__(cls, name, abbrev=None, |
| latex_repr=None, pretty_unicode_repr=None, |
| pretty_ascii_repr=None, mathml_presentation_repr=None, |
| is_prefixed=False, |
| **assumptions): |
|
|
| if not isinstance(name, Symbol): |
| name = Symbol(name) |
|
|
| if abbrev is None: |
| abbrev = name |
| elif isinstance(abbrev, str): |
| abbrev = Symbol(abbrev) |
|
|
| |
| cls._is_prefixed = is_prefixed |
|
|
| 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 |
| obj._is_prefixed = is_prefixed |
| return obj |
|
|
| 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) |
| if isinstance(scale_factor, Prefix): |
| self._is_prefixed = True |
| |
| 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 |
|
|
| 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() |
|
|
| @property |
| def is_prefixed(self): |
| """Whether or not the quantity is prefixed. Eg. `kilogram` is prefixed, but `gram` is not.""" |
| return self._is_prefixed |
|
|
| class PhysicalConstant(Quantity): |
| """Represents a physical constant, eg. `speed_of_light` or `avogadro_constant`.""" |
|
|
| is_physical_constant = True |
|
|
