Source code for astropy.units.format.vounit

# Licensed under a 3-clause BSD style license - see LICENSE.rst
Handles the "VOUnit" unit format.

import copy
import keyword
import operator
import re
import warnings

from . import core, generic, utils

[docs]class VOUnit(generic.Generic): """ The IVOA standard for units used by the VO. This is an implementation of `Units in the VO 1.0 <>`_. """ _explicit_custom_unit_regex = re.compile(r"^[YZEPTGMkhdcmunpfazy]?'((?!\d)\w)+'$") _custom_unit_regex = re.compile(r"^((?!\d)\w)+$") _custom_units = {} @staticmethod def _generate_unit_names(): from astropy import units as u from astropy.units import required_by_vounit as uvo names = {} deprecated_names = set() bases = [ "A", "C", "D", "F", "G", "H", "Hz", "J", "Jy", "K", "N", "Ohm", "Pa", "R", "Ry", "S", "T", "V", "W", "Wb", "a", "adu", "arcmin", "arcsec", "barn", "beam", "bin", "cd", "chan", "count", "ct", "d", "deg", "eV", "erg", "g", "h", "lm", "lx", "lyr", "m", "mag", "min", "mol", "pc", "ph", "photon", "pix", "pixel", "rad", "rad", "s", "solLum", "solMass", "solRad", "sr", "u", "voxel", "yr", ] # fmt: skip binary_bases = ["bit", "byte", "B"] simple_units = ["Angstrom", "angstrom", "AU", "au", "Ba", "dB", "mas"] si_prefixes = [ "y", "z", "a", "f", "p", "n", "u", "m", "c", "d", "", "da", "h", "k", "M", "G", "T", "P", "E", "Z", "Y" ] # fmt: skip binary_prefixes = ["Ki", "Mi", "Gi", "Ti", "Pi", "Ei"] deprecated_units = { "a", "angstrom", "Angstrom", "au", "Ba", "barn", "ct", "erg", "G", "ph", "pix", } # fmt: skip def do_defines(bases, prefixes, skips=[]): for base in bases: for prefix in prefixes: key = prefix + base if key in skips: continue if keyword.iskeyword(key): continue names[key] = getattr(u if hasattr(u, key) else uvo, key) if base in deprecated_units: deprecated_names.add(key) do_defines(bases, si_prefixes, ["pct", "pcount", "yd"]) do_defines(binary_bases, si_prefixes + binary_prefixes, ["dB", "dbyte"]) do_defines(simple_units, [""]) return names, deprecated_names, []
[docs] @classmethod def parse(cls, s, debug=False): if s in ("unknown", "UNKNOWN"): return None if s == "": return core.dimensionless_unscaled # Check for excess solidi, but exclude fractional exponents (allowed) if s.count("/") > 1 and s.count("/") - len(re.findall(r"\(\d+/\d+\)", s)) > 1: raise core.UnitsError( f"'{s}' contains multiple slashes, which is " "disallowed by the VOUnit standard." ) result = cls._do_parse(s, debug=debug) if hasattr(result, "function_unit"): raise ValueError("Function units are not yet supported in VOUnit.") return result
@classmethod def _get_unit(cls, t): try: return super()._get_unit(t) except ValueError: if cls._explicit_custom_unit_regex.match(t.value): return cls._def_custom_unit(t.value) if cls._custom_unit_regex.match(t.value): warnings.warn( f"Unit {t.value!r} not supported by the VOUnit standard. " + utils.did_you_mean_units( t.value, cls._units, cls._deprecated_units, cls._to_decomposed_alternative, ), core.UnitsWarning, ) return cls._def_custom_unit(t.value) raise @classmethod def _parse_unit(cls, unit, detailed_exception=True): if unit not in cls._units: raise ValueError() if unit in cls._deprecated_units: utils.unit_deprecation_warning( unit, cls._units[unit], "VOUnit", cls._to_decomposed_alternative ) return cls._units[unit] @classmethod def _get_unit_name(cls, unit): # The da- and d- prefixes are discouraged. This has the # effect of adding a scale to value in the result. if isinstance(unit, core.PrefixUnit): if unit._represents.scale == 10.0: raise ValueError( f"In '{unit}': VOUnit can not represent units with the 'da' " "(deka) prefix" ) elif unit._represents.scale == 0.1: raise ValueError( f"In '{unit}': VOUnit can not represent units with the 'd' " "(deci) prefix" ) name = unit.get_format_name("vounit") if unit in cls._custom_units.values(): return name if name not in cls._units: raise ValueError(f"Unit {name!r} is not part of the VOUnit standard") if name in cls._deprecated_units: utils.unit_deprecation_warning( name, unit, "VOUnit", cls._to_decomposed_alternative ) return name @classmethod def _def_custom_unit(cls, unit): def def_base(name): if name in cls._custom_units: return cls._custom_units[name] if name.startswith("'"): return core.def_unit( [name[1:-1], name], format={"vounit": name}, namespace=cls._custom_units, ) else: return core.def_unit(name, namespace=cls._custom_units) if unit in cls._custom_units: return cls._custom_units[unit] for short, full, factor in core.si_prefixes: for prefix in short: if unit.startswith(prefix): base_name = unit[len(prefix) :] base_unit = def_base(base_name) return core.PrefixUnit( [prefix + x for x in base_unit.names], core.CompositeUnit( factor, [base_unit], [1], _error_check=False ), format={"vounit": prefix + base_unit.names[-1]}, namespace=cls._custom_units, ) return def_base(unit) @classmethod def _format_unit_list(cls, units): out = [] units.sort(key=lambda x: cls._get_unit_name(x[0]).lower()) for base, power in units: if power == 1: out.append(cls._get_unit_name(base)) else: power = utils.format_power(power) if "/" in power or "." in power: out.append(f"{cls._get_unit_name(base)}({power})") else: out.append(f"{cls._get_unit_name(base)}**{power}") return ".".join(out)
[docs] @classmethod def to_string(cls, unit): from astropy.units import core # Remove units that aren't known to the format unit = utils.decompose_to_known_units(unit, cls._get_unit_name) if isinstance(unit, core.CompositeUnit): if unit.physical_type == "dimensionless" and unit.scale != 1: raise core.UnitScaleError( "The VOUnit format is not able to " "represent scale for dimensionless units. " f"Multiply your data by {unit.scale:e}." ) s = "" if unit.scale != 1: s += f"{unit.scale:.8g}" pairs = list(zip(unit.bases, unit.powers)) pairs.sort(key=operator.itemgetter(1), reverse=True) s += cls._format_unit_list(pairs) elif isinstance(unit, core.NamedUnit): s = cls._get_unit_name(unit) return s
@classmethod def _to_decomposed_alternative(cls, unit): from astropy.units import core try: s = cls.to_string(unit) except core.UnitScaleError: scale = unit.scale unit = copy.copy(unit) unit._scale = 1.0 return f"{cls.to_string(unit)} (with data multiplied by {scale})" return s