Merge pull request #21 from ngoldbaum/prefix-units

store SI-prefixability metadata in the unit registry

unyt/_unit_lookup_table.py

@@ -60,160 +60,164 @@
 
 default_unit_symbol_lut = {
     # base
-    "m": (1.0, dimensions.length, 0.0, r"\rm{m}"),
-    "g":  (1.0e-3, dimensions.mass, 0.0, r"\rm{g}"),
-    "s":  (1.0, dimensions.time, 0.0, r"\rm{s}"),
-    "K":  (1.0, dimensions.temperature, 0.0, r"\rm{K}"),
-    "radian": (1.0, dimensions.angle, 0.0, r"\rm{radian}"),
-    "A": (1.0, dimensions.current_mks, 0.0, r"\rm{A}"),
-    "cd": (1.0, dimensions.luminous_intensity, 0.0, r"\rm{cd}"),
-    "mol": (1.0 / amu_grams, dimensions.dimensionless, 0.0, r"\rm{mol}"),
+    "m": (1.0, dimensions.length, 0.0, r"\rm{m}", True),
+    "g":  (1.0e-3, dimensions.mass, 0.0, r"\rm{g}", True),
+    "s":  (1.0, dimensions.time, 0.0, r"\rm{s}", True),
+    "K":  (1.0, dimensions.temperature, 0.0, r"\rm{K}", True),
+    "radian": (1.0, dimensions.angle, 0.0, r"\rm{radian}", True),
+    "A": (1.0, dimensions.current_mks, 0.0, r"\rm{A}", True),
+    "cd": (1.0, dimensions.luminous_intensity, 0.0, r"\rm{cd}", True),
+    "mol": (1.0 / amu_grams, dimensions.dimensionless, 0.0, r"\rm{mol}", True),
 
     # some cgs
-    "dyne": (1.0e-5, dimensions.force, 0.0, r"\rm{dyn}"),
-    "erg":  (1.0e-7, dimensions.energy, 0.0, r"\rm{erg}"),
-    "Ba": (0.1, dimensions.pressure, 0.0, r"\rm{Ba}"),
-    "esu":  (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{esu}"),
-    "gauss": (0.1**0.5, dimensions.magnetic_field_cgs, 0.0, r"\rm{G}"),
-    "degC": (1.0, dimensions.temperature, -273.15, r"^\circ\rm{C}"),
-    "statA": (1.0e-3**1.5, dimensions.current_cgs, 0.0, r"\rm{statA}"),
+    "dyne": (1.0e-5, dimensions.force, 0.0, r"\rm{dyn}", True),
+    "erg":  (1.0e-7, dimensions.energy, 0.0, r"\rm{erg}", True),
+    "Ba": (0.1, dimensions.pressure, 0.0, r"\rm{Ba}", True),
+    "esu":  (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{esu}", True),
+    "gauss": (0.1**0.5, dimensions.magnetic_field_cgs, 0.0, r"\rm{G}", True),
+    "degC": (1.0, dimensions.temperature, -273.15, r"^\circ\rm{C}", True),
+    "statA": (1.0e-3**1.5, dimensions.current_cgs, 0.0, r"\rm{statA}", True),
     "statV": (0.1*1.0e-3**0.5, dimensions.electric_potential_cgs,
-              0.0, r"\rm{statV}"),
-    "statohm": (100.0, dimensions.resistance_cgs, 0.0, r"\rm{statohm}"),
-    "Mx": (1.0e-3**1.5, dimensions.magnetic_flux_cgs, 0.0, r"\rm{Mx}"),
+              0.0, r"\rm{statV}", True),
+    "statohm": (100.0, dimensions.resistance_cgs, 0.0, r"\rm{statohm}", True),
+    "Mx": (1.0e-3**1.5, dimensions.magnetic_flux_cgs, 0.0, r"\rm{Mx}", True),
 
     # some SI
-    "J": (1.0, dimensions.energy, 0.0, r"\rm{J}"),
-    "W": (1.0, dimensions.power, 0.0, r"\rm{W}"),
-    "Hz": (1.0, dimensions.rate, 0.0, r"\rm{Hz}"),
-    "N": (1.0, dimensions.force, 0.0, r"\rm{N}"),
-    "C": (1.0, dimensions.charge_mks, 0.0, r"\rm{C}"),
-    "T": (1.0, dimensions.magnetic_field_mks, 0.0, r"\rm{T}"),
-    "Pa": (1.0, dimensions.pressure, 0.0, r"\rm{Pa}"),
-    "V": (1.0, dimensions.electric_potential_mks, 0.0, r"\rm{V}"),
-    "ohm": (1.0, dimensions.resistance_mks, 0.0, r"\Omega"),
-    "Wb": (1.0, dimensions.magnetic_flux_mks, 0.0, r"\rm{Wb}"),
-    "lm": (1.0, dimensions.luminous_flux, 0.0, r"\rm{lm}"),
-    "lx": (1.0, dimensions.luminous_flux/dimensions.area, 0.0, r"\rm{lx}"),
+    "J": (1.0, dimensions.energy, 0.0, r"\rm{J}", True),
+    "W": (1.0, dimensions.power, 0.0, r"\rm{W}", True),
+    "Hz": (1.0, dimensions.rate, 0.0, r"\rm{Hz}", True),
+    "N": (1.0, dimensions.force, 0.0, r"\rm{N}", True),
+    "C": (1.0, dimensions.charge_mks, 0.0, r"\rm{C}", True),
+    "T": (1.0, dimensions.magnetic_field_mks, 0.0, r"\rm{T}", True),
+    "Pa": (1.0, dimensions.pressure, 0.0, r"\rm{Pa}", True),
+    "V": (1.0, dimensions.electric_potential_mks, 0.0, r"\rm{V}", True),
+    "ohm": (1.0, dimensions.resistance_mks, 0.0, r"\Omega", True),
+    "Wb": (1.0, dimensions.magnetic_flux_mks, 0.0, r"\rm{Wb}", True),
+    "lm": (1.0, dimensions.luminous_flux, 0.0, r"\rm{lm}", True),
+    "lx": (1.0, dimensions.luminous_flux/dimensions.area, 0.0, r"\rm{lx}",
+           True),
 
     # Imperial and other non-metric units
-    "inch": (m_per_inch, dimensions.length, 0.0, r"\rm{in}"),
-    "ft": (m_per_ft, dimensions.length, 0.0, r"\rm{ft}"),
-    "yd": (0.9144, dimensions.length, 0.0, r"\rm{yd}"),
-    "mile": (1609.344, dimensions.length, 0.0, r"\rm{mile}"),
-    "fur": (m_per_ft*660.0, dimensions.length, 0.0, r"\rm{fur}"),
+    "inch": (m_per_inch, dimensions.length, 0.0, r"\rm{in}", False),
+    "ft": (m_per_ft, dimensions.length, 0.0, r"\rm{ft}", False),
+    "yd": (0.9144, dimensions.length, 0.0, r"\rm{yd}", False),
+    "mile": (1609.344, dimensions.length, 0.0, r"\rm{mile}", False),
+    "fur": (m_per_ft*660.0, dimensions.length, 0.0, r"\rm{fur}", False),
     "degF": (kelvin_per_rankine, dimensions.temperature, -459.67,
-             "^\circ\rm{F}"),
-    "R": (kelvin_per_rankine, dimensions.temperature, 0.0, r"^\circ\rm{R}"),
+             "^\circ\rm{F}", False),
+    "R": (kelvin_per_rankine, dimensions.temperature, 0.0, r"^\circ\rm{R}",
+          False),
     "lbf": (kg_per_pound*standard_gravity_m_per_s2,
-            dimensions.force, 0.0, r"\rm{lbf}"),
-    "lb": (kg_per_pound, dimensions.mass, 0.0, r"\rm{lb}"),
-    "lbm": (kg_per_pound, dimensions.mass, 0.0, r"\rm{lbm}"),
-    "atm": (pascal_per_atm, dimensions.pressure, 0.0, r"\rm{atm}"),
-    "hp": (watt_per_horsepower, dimensions.power, 0.0, r"\rm{hp}"),
-    "oz": (kg_per_pound/16.0, dimensions.mass, 0.0, r"\rm{oz}"),
-    "ton": (kg_per_pound*2000.0, dimensions.mass, 0.0, r"\rm{ton}"),
+            dimensions.force, 0.0, r"\rm{lbf}", False),
+    "lb": (kg_per_pound, dimensions.mass, 0.0, r"\rm{lb}", False),
+    "lbm": (kg_per_pound, dimensions.mass, 0.0, r"\rm{lbm}", False),
+    "atm": (pascal_per_atm, dimensions.pressure, 0.0, r"\rm{atm}", False),
+    "hp": (watt_per_horsepower, dimensions.power, 0.0, r"\rm{hp}", False),
+    "oz": (kg_per_pound/16.0, dimensions.mass, 0.0, r"\rm{oz}", False),
+    "ton": (kg_per_pound*2000.0, dimensions.mass, 0.0, r"\rm{ton}", False),
     "slug": (kg_per_pound*standard_gravity_m_per_s2/m_per_ft,
-             dimensions.mass, 0.0, r"\rm{slug}"),
-    "cal": (4.184, dimensions.energy, 0.0, r"\rm{cal}"),
-    "BTU": (1055.0559, dimensions.energy, 0.0, r"\rm{BTU}"),
+             dimensions.mass, 0.0, r"\rm{slug}", False),
+    "cal": (4.184, dimensions.energy, 0.0, r"\rm{cal}", True),
+    "BTU": (1055.0559, dimensions.energy, 0.0, r"\rm{BTU}", False),
     "psi": (kg_per_pound*standard_gravity_m_per_s2/m_per_inch**2,
-            dimensions.pressure, 0.0, r"\rm{psi}"),
-    "smoot": (1.7018, dimensions.length, 0.0, r"\rm{smoot}"),
+            dimensions.pressure, 0.0, r"\rm{psi}", False),
+    "smoot": (1.7018, dimensions.length, 0.0, r"\rm{smoot}", False),
 
     # dimensionless stuff
-    "h": (1.0, dimensions.dimensionless, 0.0, r"h"),
-    "dimensionless": (1.0, dimensions.dimensionless, 0.0, r""),
+    "h": (1.0, dimensions.dimensionless, 0.0, r"h", False),
+    "dimensionless": (1.0, dimensions.dimensionless, 0.0, r"", False),
 
     # times
-    "min": (sec_per_min, dimensions.time, 0.0, r"\rm{min}"),
-    "hr":  (sec_per_hr, dimensions.time, 0.0, r"\rm{hr}"),
-    "day": (sec_per_day, dimensions.time, 0.0, r"\rm{d}"),
-    "d": (sec_per_day, dimensions.time, 0.0, r"\rm{d}"),
-    "yr":  (sec_per_year, dimensions.time, 0.0, r"\rm{yr}"),
+    "min": (sec_per_min, dimensions.time, 0.0, r"\rm{min}", False),
+    "hr":  (sec_per_hr, dimensions.time, 0.0, r"\rm{hr}", False),
+    "day": (sec_per_day, dimensions.time, 0.0, r"\rm{d}", False),
+    "d": (sec_per_day, dimensions.time, 0.0, r"\rm{d}", False),
+    "yr":  (sec_per_year, dimensions.time, 0.0, r"\rm{yr}", True),
 
     # Velocities
-    "c": (speed_of_light_m_per_s, dimensions.velocity, 0.0, r"\rm{c}"),
+    "c": (speed_of_light_m_per_s, dimensions.velocity, 0.0, r"\rm{c}", False),
 
     # Solar units
-    "Msun": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot"),
-    "msun": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot"),
-    "Rsun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot"),
-    "rsun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot"),
-    "R_sun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot"),
-    "r_sun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot"),
-    "Lsun": (luminosity_sun_watts, dimensions.power, 0.0, r"L_\odot"),
-    "Tsun": (temp_sun_kelvin, dimensions.temperature, 0.0, r"T_\odot"),
-    "Zsun": (metallicity_sun, dimensions.dimensionless, 0.0, r"Z_\odot"),
-    "Mjup": (mass_jupiter_kg, dimensions.mass, 0.0, r"M_{\rm{Jup}}"),
-    "Mearth": (mass_earth_kg, dimensions.mass, 0.0, r"M_\oplus"),
+    "Msun": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot", False),
+    "msun": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot", False),
+    "Rsun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot", False),
+    "rsun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot", False),
+    "R_sun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot", False),
+    "r_sun": (m_per_rsun, dimensions.length, 0.0, r"R_\odot", False),
+    "Lsun": (luminosity_sun_watts, dimensions.power, 0.0, r"L_\odot", False),
+    "Tsun": (temp_sun_kelvin, dimensions.temperature, 0.0, r"T_\odot", False),
+    "Zsun": (metallicity_sun, dimensions.dimensionless, 0.0, r"Z_\odot",
+             False),
+    "Mjup": (mass_jupiter_kg, dimensions.mass, 0.0, r"M_{\rm{Jup}}", False),
+    "Mearth": (mass_earth_kg, dimensions.mass, 0.0, r"M_\oplus", False),
+    "R_jup": (m_per_rjup, dimensions.length, 0.0, r"R_\mathrm{Jup}", False),
+    "r_jup": (m_per_rjup, dimensions.length, 0.0, r"R_\mathrm{Jup}", False),
+    "R_earth": (m_per_rearth, dimensions.length, 0.0, r"R_\oplus", False),
+    "r_earth": (m_per_rearth, dimensions.length, 0.0, r"R_\oplus", False),
 
     # astro distances
-    "AU": (m_per_au, dimensions.length, 0.0, r"\rm{AU}"),
-    "au": (m_per_au, dimensions.length, 0.0, r"\rm{AU}"),
-    "ly": (m_per_ly, dimensions.length, 0.0, r"\rm{ly}"),
-    "pc": (m_per_pc, dimensions.length, 0.0, r"\rm{pc}"),
+    "AU": (m_per_au, dimensions.length, 0.0, r"\rm{AU}", False),
+    "au": (m_per_au, dimensions.length, 0.0, r"\rm{AU}", False),
+    "ly": (m_per_ly, dimensions.length, 0.0, r"\rm{ly}", False),
+    "pc": (m_per_pc, dimensions.length, 0.0, r"\rm{pc}", True),
 
     # angles
-    "degree": (np.pi/180., dimensions.angle, 0.0, r"\rm{deg}"),  # degrees
+    "degree": (np.pi/180., dimensions.angle, 0.0, r"\rm{deg}", False),
     "arcmin": (np.pi/10800., dimensions.angle, 0.0,
-               r"\rm{arcmin}"),  # arcminutes
+               r"\rm{arcmin}", False),  # arcminutes
     "arcsec": (np.pi/648000., dimensions.angle, 0.0,
-               r"\rm{arcsec}"),  # arcseconds
+               r"\rm{arcsec}", False),  # arcseconds
     "mas": (np.pi/648000000., dimensions.angle, 0.0,
-            r"\rm{mas}"),  # milliarcseconds
-    "hourangle": (np.pi/12., dimensions.angle, 0.0, r"\rm{HA}"),  # hour angle
-    "steradian": (1.0, dimensions.solid_angle, 0.0, r"\rm{sr}"),
-    "lat": (-np.pi/180.0, dimensions.angle, 90.0, r"\rm{Latitude}"),
-    "lon": (np.pi/180.0, dimensions.angle, -180.0, r"\rm{Longitude}"),
+            r"\rm{mas}", False),  # milliarcseconds
+    "hourangle": (np.pi/12., dimensions.angle, 0.0, r"\rm{HA}", False),
+    "steradian": (1.0, dimensions.solid_angle, 0.0, r"\rm{sr}", False),
+    "lat": (-np.pi/180.0, dimensions.angle, 90.0, r"\rm{Latitude}", False),
+    "lon": (np.pi/180.0, dimensions.angle, -180.0, r"\rm{Longitude}", False),
 
     # misc
-    "eV": (J_per_eV, dimensions.energy, 0.0, r"\rm{eV}"),
-    "amu": (amu_kg, dimensions.mass, 0.0, r"\rm{amu}"),
-    "angstrom": (m_per_ang, dimensions.length, 0.0, r"\AA"),
-    "Jy": (jansky_mks, dimensions.specific_flux, 0.0, r"\rm{Jy}"),
-    "counts": (1.0, dimensions.dimensionless, 0.0, r"\rm{counts}"),
-    "photons": (1.0, dimensions.dimensionless, 0.0, r"\rm{photons}"),
-    "me": (mass_electron_kg, dimensions.mass, 0.0, r"m_e"),
-    "mp": (mass_hydrogen_kg, dimensions.mass, 0.0, r"m_p"),
-    'Sv': (1.0, dimensions.specific_energy, 0.0, r"\rm{Sv}"),
-    "rayleigh": (2.5e9/np.pi, dimensions.count_intensity, 0.0, r"\rm{R}"),
-    "lambert": (1.0e4/np.pi, dimensions.luminance, 0.0, r"\rm{L}"),
-    "nt": (1.0, dimensions.luminance, 0.0, r"\rm{nt}"),
+    "eV": (J_per_eV, dimensions.energy, 0.0, r"\rm{eV}", True),
+    "amu": (amu_kg, dimensions.mass, 0.0, r"\rm{amu}", False),
+    "angstrom": (m_per_ang, dimensions.length, 0.0, r"\AA", False),
+    "Jy": (jansky_mks, dimensions.specific_flux, 0.0, r"\rm{Jy}", True),
+    "counts": (1.0, dimensions.dimensionless, 0.0, r"\rm{counts}", False),
+    "photons": (1.0, dimensions.dimensionless, 0.0, r"\rm{photons}", False),
+    "me": (mass_electron_kg, dimensions.mass, 0.0, r"m_e", False),
+    "mp": (mass_hydrogen_kg, dimensions.mass, 0.0, r"m_p", False),
+    'Sv': (1.0, dimensions.specific_energy, 0.0, r"\rm{Sv}", True),
+    "rayleigh": (2.5e9/np.pi, dimensions.count_intensity, 0.0, r"\rm{R}",
+                 False),
+    "lambert": (1.0e4/np.pi, dimensions.luminance, 0.0, r"\rm{L}", False),
+    "nt": (1.0, dimensions.luminance, 0.0, r"\rm{nt}", False),
 
     # for AstroPy compatibility
-    "solMass": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot"),
-    "solRad": (m_per_rsun, dimensions.length, 0.0, r"R_\odot"),
-    "solLum": (luminosity_sun_watts, dimensions.power, 0.0, r"L_\odot"),
-    "dyn": (1.0e-5, dimensions.force, 0.0, r"\rm{dyn}"),
-    "sr": (1.0, dimensions.solid_angle, 0.0, r"\rm{sr}"),
-    "rad": (1.0, dimensions.angle, 0.0, r"\rm{rad}"),
-    "deg": (np.pi/180., dimensions.angle, 0.0, r"\rm{deg}"),
-    "Fr":  (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{Fr}"),
-    "G": (0.1**0.5, dimensions.magnetic_field_cgs, 0.0, r"\rm{G}"),
-    "Angstrom": (m_per_ang, dimensions.length, 0.0, r"\AA"),
-    "statC": (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{statC}"),
+    "solMass": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot", False),
+    "solRad": (m_per_rsun, dimensions.length, 0.0, r"R_\odot", False),
+    "solLum": (luminosity_sun_watts, dimensions.power, 0.0, r"L_\odot", False),
+    "dyn": (1.0e-5, dimensions.force, 0.0, r"\rm{dyn}", False),
+    "sr": (1.0, dimensions.solid_angle, 0.0, r"\rm{sr}", False),
+    "rad": (1.0, dimensions.angle, 0.0, r"\rm{rad}", False),
+    "deg": (np.pi/180., dimensions.angle, 0.0, r"\rm{deg}", False),
+    "Fr":  (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{Fr}", False),
+    "G": (0.1**0.5, dimensions.magnetic_field_cgs, 0.0, r"\rm{G}", True),
+    "Angstrom": (m_per_ang, dimensions.length, 0.0, r"\AA", False),
+    "statC": (1.0e-3**1.5, dimensions.charge_cgs, 0.0, r"\rm{statC}", True),
 
     # Planck units
-    "m_pl": (planck_mass_kg, dimensions.mass, 0.0, r"m_{\rm{P}}"),
-    "l_pl": (planck_length_m, dimensions.length, 0.0, r"\ell_\rm{P}"),
-    "t_pl": (planck_time_s, dimensions.time, 0.0, r"t_{\rm{P}}"),
-    "T_pl": (planck_temperature_K, dimensions.temperature, 0.0, r"T_{\rm{P}}"),
-    "q_pl": (planck_charge_C, dimensions.charge_mks, 0.0, r"q_{\rm{P}}"),
-    "E_pl": (planck_energy_J, dimensions.energy, 0.0, r"E_{\rm{P}}"),
+    "m_pl": (planck_mass_kg, dimensions.mass, 0.0, r"m_{\rm{P}}", False),
+    "l_pl": (planck_length_m, dimensions.length, 0.0, r"\ell_\rm{P}", False),
+    "t_pl": (planck_time_s, dimensions.time, 0.0, r"t_{\rm{P}}", False),
+    "T_pl": (planck_temperature_K, dimensions.temperature, 0.0, r"T_{\rm{P}}",
+             False),
+    "q_pl": (planck_charge_C, dimensions.charge_mks, 0.0, r"q_{\rm{P}}",
+             False),
+    "E_pl": (planck_energy_J, dimensions.energy, 0.0, r"E_{\rm{P}}", False),
 
     # Geometrized units
-    "m_geom": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot"),
+    "m_geom": (mass_sun_kg, dimensions.mass, 0.0, r"M_\odot", False),
     "l_geom": (newton_mks*mass_sun_kg/speed_of_light_m_per_s**2,
-               dimensions.length, 0.0, r"M_\odot"),
+               dimensions.length, 0.0, r"M_\odot", False),
     "t_geom": (newton_mks*mass_sun_kg/speed_of_light_m_per_s**3,
-               dimensions.time, 0.0, r"M_\odot"),
-
-    # Some Solar System units
-    "R_earth": (m_per_rearth, dimensions.length, 0.0, r"R_\oplus"),
-    "r_earth": (m_per_rearth, dimensions.length, 0.0, r"R_\oplus"),
-    "R_jup": (m_per_rjup, dimensions.length, 0.0, r"R_\mathrm{Jup}"),
-    "r_jup": (m_per_rjup, dimensions.length, 0.0, r"R_\mathrm{Jup}"),
+               dimensions.time, 0.0, r"M_\odot", False),
 }
 
 # This dictionary formatting from magnitude package, credit to Juan Reyero.
@@ -244,44 +248,6 @@
     "u": r"\mu",
     }
 
-prefixable_units = [
-    "m",
-    "pc",
-    "mcm",
-    "pccm",
-    "g",
-    "eV",
-    "s",
-    "yr",
-    "K",
-    "dyne",
-    "erg",
-    "esu",
-    "J",
-    "Hz",
-    "W",
-    "gauss",
-    "G",
-    "Jy",
-    "N",
-    "T",
-    "A",
-    "C",
-    "statA",
-    "Pa",
-    "V",
-    "statV",
-    "ohm",
-    "statohm",
-    "Sv",
-    "mol",
-    "cd",
-    "lm",
-    "lx",
-    "Wb",
-    "Mx",
-]
-
 default_base_units = {
     dimensions.mass: 'kg',
     dimensions.length: 'm',

unyt/tests/test_unit_registry.py

@@ -21,6 +21,7 @@
     SymbolNotFoundError,
     UnitParseError,
 )
+from unyt.unit_object import Unit
 from unyt.unit_registry import UnitRegistry
 
 
@@ -52,3 +53,16 @@ def test_add_modify_error():
 def test_keys():
     ureg = UnitRegistry()
     assert sorted(ureg.keys()) == sorted(ureg.lut.keys())
+
+
+def test_prefixable_units():
+    ureg = UnitRegistry()
+    pu = ureg.prefixable_units
+    assert 'm' in pu
+    assert 'pc' in pu
+    assert 'mol' in pu
+    ureg.add('foobar', 1.0, length, prefixable=True)
+    assert 'foobar' in ureg.prefixable_units
+    mfoobar = Unit('mfoobar', registry=ureg)
+    foobar = Unit('foobar', registry=ureg)
+    assert (1*foobar)/(1*mfoobar) == 1000

unyt/tests/test_unit_systems.py

@@ -53,7 +53,7 @@ def test_unit_system_id():
     reg1 = UnitRegistry()
     reg1.remove('g')
     assert reg1.unit_system_id != reg2.unit_system_id
-    reg1.add('g', 1.0e-3, dimensions.mass)
+    reg1.add('g', 1.0e-3, dimensions.mass, prefixable=True)
     assert reg1.unit_system_id == reg2.unit_system_id
 
 

unyt/tests/test_units.py

@@ -52,8 +52,7 @@
 from unyt.unit_systems import UnitSystem
 from unyt._unit_lookup_table import (
     default_unit_symbol_lut,
-    unit_prefixes,
-    prefixable_units
+    unit_prefixes
 )
 import unyt.unit_symbols as unit_symbols
 from unyt._physical_ratios import (
@@ -74,7 +73,7 @@ def test_no_conflicting_symbols():
 
     # go through all possible prefix combos
     for symbol in default_unit_symbol_lut.keys():
-        if symbol in prefixable_units:
+        if default_unit_symbol_lut[symbol][4]:
             keys = unit_prefixes.keys()
         else:
             keys = [symbol]
@@ -493,7 +492,7 @@ def test_latex_repr():
 
     # create a fake comoving unit
     registry.add('pccm', registry.lut['pc'][0]/(1+2), length,
-                 "\\rm{pc}/(1+z)")
+                 "\\rm{pc}/(1+z)", prefixable=True)
 
     test_unit = Unit('Mpccm', registry=registry)
     assert_almost_equal(test_unit.base_value, m_per_mpc/3)
@@ -656,3 +655,8 @@ def test_define_unit_error():
         define_unit('foobar', 'baz')
     with pytest.raises(RuntimeError):
         define_unit('foobar', 12)
+
+
+def test_symbol_lut_length():
+    for v in default_unit_symbol_lut.values():
+        assert len(v) == 5