Source code for unyt.unit_systems

Unit system class.


# -----------------------------------------------------------------------------
# Copyright (c) 2018, yt Development Team.
# Distributed under the terms of the Modified BSD License.
# The full license is in the LICENSE file, distributed with this software.
# -----------------------------------------------------------------------------

from collections import OrderedDict

from unyt import dimensions
from unyt._parsing import parse_unyt_expr
from unyt._unit_lookup_table import (
    default_unit_symbol_lut as default_lut,
from unyt.exceptions import IllDefinedUnitSystem, MissingMKSCurrent, UnitsNotReducible

[docs]def add_symbols(namespace, registry): """Adds the unit symbols from :mod:`unyt.unit_symbols` to a namespace Parameters ---------- namespace : dict The dict to insert unit symbols into. The keys will be string unit names and values will be the corresponding unit objects. registry : :class:`unyt.unit_registry.UnitRegistry` The registry to create units from. Note that if you would like to use a custom unit system, ensure your registry was created using that unit system. Example ------- >>> from unyt.unit_registry import UnitRegistry >>> class MyClass(): ... def __init__(self): ... self.reg = UnitRegistry() ... add_symbols(vars(self), self.reg) >>> foo = MyClass() >>> foo.kilometer km >>> foo.joule J """ import unyt.unit_symbols as us from unyt.unit_object import Unit for name, unit in vars(us).items(): if name.startswith("_"): continue namespace[name] = Unit(unit.expr, registry=registry) for name in [k for k in registry.keys() if k not in namespace]: namespace[name] = Unit(name, registry=registry)
[docs]def add_constants(namespace, registry): """Adds the quantities from :mod:`unyt.physical_constants` to a namespace Parameters ---------- namespace : dict The dict to insert quantities into. The keys will be string names and values will be the corresponding quantities. registry : :class:`unyt.unit_registry.UnitRegistry` The registry to create units from. Note that if you would like to use a custom unit system, ensure your registry was created using that unit system. Example ------- >>> from unyt.unit_registry import UnitRegistry >>> class MyClass(): ... def __init__(self): ... self.reg = UnitRegistry(unit_system='cgs') ... add_constants(vars(self), self.reg) >>> foo = MyClass() >>> foo.gravitational_constant unyt_quantity(6.67408e-08, 'cm**3/(g*s**2)') >>> foo.speed_of_light unyt_quantity(2.99792458e+10, 'cm/s') """ from unyt.array import unyt_quantity for constant_name in physical_constants: value, unit_name, alternate_names = physical_constants[constant_name] for name in alternate_names + [constant_name]: quan = unyt_quantity(value, unit_name, registry=registry) try: namespace[name] = quan.in_base(unit_system=registry.unit_system) except UnitsNotReducible: namespace[name] = quan namespace[name + "_mks"] = unyt_quantity( value, unit_name, registry=registry ) try: namespace[name + "_cgs"] = quan.in_cgs() except UnitsNotReducible: pass if name == "h": # backward compatibility for unyt 1.0, which defined hmks namespace["hmks"] = namespace["h_mks"].copy() namespace["hcgs"] = namespace["h_cgs"].copy()
def _split_prefix(symbol_str, unit_symbol_lut): possible_prefix = symbol_str[0] if symbol_str[:2] == "da": possible_prefix = "da" if possible_prefix in unit_prefixes: # the first character could be a prefix, check the rest of the symbol symbol_wo_pref = symbol_str[1:] # deca is the only prefix with length 2 if symbol_str[:2] == "da": symbol_wo_pref = symbol_str[2:] possible_prefix = "da" entry = unit_symbol_lut.get(symbol_wo_pref, None) if entry and entry[4]: return possible_prefix, symbol_wo_pref return "", symbol_str def _get_system_unit_string(dims, base_units): # The dimensions of a unit object is the product of the base dimensions. # Use sympy to factor the dimensions into base CGS unit symbols. units = [] my_dims = dims.expand() if my_dims is dimensions.dimensionless: return "" for factor in my_dims.as_ordered_factors(): dim = list(factor.free_symbols)[0] unit_string = str(base_units[dim]) if factor.is_Pow: power_string = "**(%s)" % factor.as_base_exp()[1] else: power_string = "" units.append("(%s)%s" % (unit_string, power_string)) return " * ".join(units) unit_system_registry = {} cmks = dimensions.current_mks
[docs]class UnitSystem: """ Create a UnitSystem for facilitating conversions to a default set of units. Parameters ---------- name : string The name of the unit system. Will be used as the key in the *unit_system_registry* dict to reference the unit system by. length_unit : string or :class:`unyt.unit_object.Unit` The base length unit of this unit system. mass_unit : string or :class:`unyt.unit_object.Unit` The base mass unit of this unit system. time_unit : string or :class:`unyt.unit_object.Unit` The base time unit of this unit system. temperature_unit : string or :class:`unyt.unit_object.Unit`, optional The base temperature unit of this unit system. Defaults to "K". angle_unit : string or :class:`unyt.unit_object.Unit`, optional The base angle unit of this unit system. Defaults to "rad". mks_system: boolean, optional Whether or not this unit system has SI-specific units. Default: False current_mks_unit : string or :class:`unyt.unit_object.Unit`, optional The base current unit of this unit system. Defaults to "A". luminous_intensity_unit : string or :class:`unyt.unit_object.Unit`, optional The base luminous intensity unit of this unit system. Defaults to "cd". registry : :class:`unyt.unit_registry.UnitRegistry` object The unit registry associated with this unit system. Only useful for defining unit systems based on code units. """ def __init__( self, name, length_unit, mass_unit, time_unit, temperature_unit="K", angle_unit="rad", current_mks_unit="A", luminous_intensity_unit="cd", logarithmic_unit="Np", registry=None, ): self.registry = registry self.units_map = OrderedDict( [ (dimensions.length, length_unit), (dimensions.mass, mass_unit), (dimensions.time, time_unit), (dimensions.temperature, temperature_unit), (dimensions.angle, angle_unit), (dimensions.current_mks, current_mks_unit), (dimensions.luminous_intensity, luminous_intensity_unit), (dimensions.logarithmic, logarithmic_unit), ] ) for k, v in self.units_map.items(): if v is not None: if hasattr(v, "value") and hasattr(v, "units"): self.units_map[k] = v.value * v.units.expr else: self.units_map[k] = parse_unyt_expr(str(v)) for dimension, unit in self.units_map.items(): # CGS sets the current_mks unit to none, so catch it here if unit is None and dimension is dimensions.current_mks: continue if unit.is_Mul: unit = unit.as_coeff_Mul()[1] if ( self.registry is not None and self.registry[str(unit)][1] is not dimension ): raise IllDefinedUnitSystem(self.units_map) elif self.registry is None: bu = _split_prefix(str(unit), default_lut)[1] inferred_dimension = default_lut[inv_name_alternatives[bu]][1] if inferred_dimension is not dimension: raise IllDefinedUnitSystem(self.units_map) self._dims = [ "length", "mass", "time", "temperature", "angle", "current_mks", "luminous_intensity", "logarithmic", ] self.registry = registry self.base_units = self.units_map.copy() unit_system_registry[name] = self = name def __getitem__(self, key): from unyt.unit_object import Unit if isinstance(key, str): key = getattr(dimensions, key) um = self.units_map if key not in um or um[key] is None: if cmks in key.free_symbols and self.units_map[cmks] is None: raise MissingMKSCurrent( units = _get_system_unit_string(key, self.units_map) self.units_map[key] = parse_unyt_expr(units) return Unit(units, registry=self.registry) return Unit(self.units_map[key], registry=self.registry) def __setitem__(self, key, value): if isinstance(key, str): if key not in self._dims: self._dims.append(key) key = getattr(dimensions, key) if self.units_map[cmks] is None and cmks in key.free_symbols: raise MissingMKSCurrent( self.units_map[key] = parse_unyt_expr(str(value)) def __str__(self): return def __repr__(self): repr = "%s Unit System\n" % repr += " Base Units:\n" for dim in self.base_units: if self.base_units[dim] is not None: repr += " %s: %s\n" % (str(dim).strip("()"), self.base_units[dim]) repr += " Other Units:\n" for key in self._dims: dim = getattr(dimensions, key) if dim not in self.base_units: repr += " %s: %s\n" % (key, self.units_map[dim]) return repr[:-1] @property def has_current_mks(self): """Does this unit system have an MKS current dimension?""" return self.units_map[cmks] is not None
#: The CGS unit system cgs_unit_system = UnitSystem("cgs", "cm", "g", "s", current_mks_unit=None) cgs_unit_system["energy"] = "erg" cgs_unit_system["specific_energy"] = "erg/g" cgs_unit_system["pressure"] = "dyne/cm**2" cgs_unit_system["force"] = "dyne" cgs_unit_system["magnetic_field_cgs"] = "gauss" cgs_unit_system["charge_cgs"] = "esu" cgs_unit_system["current_cgs"] = "statA" cgs_unit_system["power"] = "erg/s" #: The MKS unit system mks_unit_system = UnitSystem("mks", "m", "kg", "s") mks_unit_system["energy"] = "J" mks_unit_system["specific_energy"] = "J/kg" mks_unit_system["pressure"] = "Pa" mks_unit_system["force"] = "N" mks_unit_system["magnetic_field"] = "T" mks_unit_system["charge"] = "C" mks_unit_system["frequency"] = "Hz" mks_unit_system["power"] = "W" mks_unit_system["electric_potential"] = "V" mks_unit_system["capacitance"] = "F" mks_unit_system["inductance"] = "H" mks_unit_system["resistance"] = "ohm" mks_unit_system["magnetic_flux"] = "Wb" mks_unit_system["luminous_flux"] = "lm" #: The imperial unit system imperial_unit_system = UnitSystem("imperial", "ft", "lb", "s", temperature_unit="R") imperial_unit_system["force"] = "lbf" imperial_unit_system["energy"] = "ft*lbf" imperial_unit_system["pressure"] = "lbf/ft**2" imperial_unit_system["power"] = "hp" #: The galactic unit system galactic_unit_system = UnitSystem("galactic", "kpc", "Msun", "Myr") galactic_unit_system["energy"] = "keV" galactic_unit_system["magnetic_field_cgs"] = "uG" #: The solar unit system solar_unit_system = UnitSystem("solar", "AU", "Mearth", "yr") #: Geometrized unit system geometrized_unit_system = UnitSystem("geometrized", "l_geom", "m_geom", "t_geom") #: Planck unit system planck_unit_system = UnitSystem( "planck", "l_pl", "m_pl", "t_pl", temperature_unit="T_pl" ) planck_unit_system["energy"] = "E_pl" planck_unit_system["charge_mks"] = "q_pl"