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""" |
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Physical quantities. |
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""" |
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from sympy.core.expr import AtomicExpr |
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from sympy.core.symbol import Symbol |
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from sympy.core.sympify import sympify |
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from sympy.physics.units.dimensions import _QuantityMapper |
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from sympy.physics.units.prefixes import Prefix |
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class Quantity(AtomicExpr): |
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""" |
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Physical quantity: can be a unit of measure, a constant or a generic quantity. |
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""" |
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is_commutative = True |
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is_real = True |
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is_number = False |
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is_nonzero = True |
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is_physical_constant = False |
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_diff_wrt = True |
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def __new__(cls, name, abbrev=None, |
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latex_repr=None, pretty_unicode_repr=None, |
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pretty_ascii_repr=None, mathml_presentation_repr=None, |
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is_prefixed=False, |
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**assumptions): |
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if not isinstance(name, Symbol): |
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name = Symbol(name) |
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if abbrev is None: |
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abbrev = name |
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elif isinstance(abbrev, str): |
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abbrev = Symbol(abbrev) |
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cls._is_prefixed = is_prefixed |
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obj = AtomicExpr.__new__(cls, name, abbrev) |
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obj._name = name |
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obj._abbrev = abbrev |
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obj._latex_repr = latex_repr |
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obj._unicode_repr = pretty_unicode_repr |
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obj._ascii_repr = pretty_ascii_repr |
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obj._mathml_repr = mathml_presentation_repr |
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obj._is_prefixed = is_prefixed |
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return obj |
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def set_global_dimension(self, dimension): |
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_QuantityMapper._quantity_dimension_global[self] = dimension |
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def set_global_relative_scale_factor(self, scale_factor, reference_quantity): |
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""" |
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Setting a scale factor that is valid across all unit system. |
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""" |
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from sympy.physics.units import UnitSystem |
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scale_factor = sympify(scale_factor) |
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if isinstance(scale_factor, Prefix): |
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self._is_prefixed = True |
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scale_factor = scale_factor.replace( |
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lambda x: isinstance(x, Prefix), |
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lambda x: x.scale_factor |
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) |
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scale_factor = sympify(scale_factor) |
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UnitSystem._quantity_scale_factors_global[self] = (scale_factor, reference_quantity) |
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UnitSystem._quantity_dimensional_equivalence_map_global[self] = reference_quantity |
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@property |
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def name(self): |
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return self._name |
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@property |
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def dimension(self): |
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from sympy.physics.units import UnitSystem |
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unit_system = UnitSystem.get_default_unit_system() |
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return unit_system.get_quantity_dimension(self) |
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@property |
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def abbrev(self): |
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""" |
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Symbol representing the unit name. |
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Prepend the abbreviation with the prefix symbol if it is defines. |
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""" |
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return self._abbrev |
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@property |
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def scale_factor(self): |
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""" |
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Overall magnitude of the quantity as compared to the canonical units. |
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""" |
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from sympy.physics.units import UnitSystem |
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unit_system = UnitSystem.get_default_unit_system() |
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return unit_system.get_quantity_scale_factor(self) |
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def _eval_is_positive(self): |
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return True |
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def _eval_is_constant(self): |
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return True |
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def _eval_Abs(self): |
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return self |
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def _eval_subs(self, old, new): |
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if isinstance(new, Quantity) and self != old: |
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return self |
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def _latex(self, printer): |
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if self._latex_repr: |
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return self._latex_repr |
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else: |
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return r'\text{{{}}}'.format(self.args[1] \ |
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if len(self.args) >= 2 else self.args[0]) |
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def convert_to(self, other, unit_system="SI"): |
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""" |
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Convert the quantity to another quantity of same dimensions. |
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Examples |
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======== |
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>>> from sympy.physics.units import speed_of_light, meter, second |
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>>> speed_of_light |
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speed_of_light |
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>>> speed_of_light.convert_to(meter/second) |
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299792458*meter/second |
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>>> from sympy.physics.units import liter |
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>>> liter.convert_to(meter**3) |
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meter**3/1000 |
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""" |
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from .util import convert_to |
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return convert_to(self, other, unit_system) |
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@property |
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def free_symbols(self): |
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"""Return free symbols from quantity.""" |
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return set() |
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@property |
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def is_prefixed(self): |
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"""Whether or not the quantity is prefixed. Eg. `kilogram` is prefixed, but `gram` is not.""" |
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return self._is_prefixed |
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class PhysicalConstant(Quantity): |
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"""Represents a physical constant, eg. `speed_of_light` or `avogadro_constant`.""" |
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is_physical_constant = True |
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