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 <http://www.ivoa.net/Documents/VOUnits/>`_. """ _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' ] 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' ] binary_prefixes = [ 'Ki', 'Mi', 'Gi', 'Ti', 'Pi', 'Ei' ] deprecated_units = set([ 'a', 'angstrom', 'Angstrom', 'au', 'Ba', 'barn', 'ct', 'erg', 'G', 'ph', 'pix' ]) 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( "'{0}' contains multiple slashes, which is " "disallowed by the VOUnit standard".format(s)) 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 _parse_unit(cls, unit, detailed_exception=True): if unit not in cls._units: if cls._explicit_custom_unit_regex.match(unit): return cls._def_custom_unit(unit) if not cls._custom_unit_regex.match(unit): raise ValueError() warnings.warn( "Unit {0!r} not supported by the VOUnit " "standard. {1}".format( unit, utils.did_you_mean_units( unit, cls._units, cls._deprecated_units, cls._to_decomposed_alternative)), core.UnitsWarning) return cls._def_custom_unit(unit) 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( "In '{0}': VOUnit can not represent units with the 'da' " "(deka) prefix".format(unit)) elif unit._represents.scale == 0.1: raise ValueError( "In '{0}': VOUnit can not represent units with the 'd' " "(deci) prefix".format(unit)) name = unit.get_format_name('vounit') if unit in cls._custom_units.values(): return name if name not in cls._units: raise ValueError( "Unit {0!r} is not part of the VOUnit standard".format(name)) 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)
[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. " "Multiply your data by {0:e}." .format(unit.scale)) s = '' if unit.scale != 1: m, ex = utils.split_mantissa_exponent(unit.scale) parts = [] if m: parts.append(m) if ex: fex = '10' if not ex.startswith('-'): fex += '+' fex += ex parts.append(fex) s += ' '.join(parts) 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 '{0} (with data multiplied by {1})'.format( cls.to_string(unit), scale) return s