Source code for astropy.units.format.fits

# Licensed under a 3-clause BSD style license - see LICENSE.rst

"""
Handles the "FITS" unit format.
"""


import numpy as np

import copy
import keyword
import operator

from . import core, generic, utils


[docs]class Fits(generic.Generic): """ The FITS standard unit format. This supports the format defined in the Units section of the `FITS Standard <https://fits.gsfc.nasa.gov/fits_standard.html>`_. """ name = 'fits' @staticmethod def _generate_unit_names(): from astropy import units as u names = {} deprecated_names = set() # Note about deprecated units: before v2.0, several units were treated # as deprecated (G, barn, erg, Angstrom, angstrom). However, in the # FITS 3.0 standard, these units are explicitly listed in the allowed # units, but deprecated in the IAU Style Manual (McNally 1988). So # after discussion (https://github.com/astropy/astropy/issues/2933), # these units have been removed from the lists of deprecated units and # bases. bases = [ 'm', 'g', 's', 'rad', 'sr', 'K', 'A', 'mol', 'cd', 'Hz', 'J', 'W', 'V', 'N', 'Pa', 'C', 'Ohm', 'S', 'F', 'Wb', 'T', 'H', 'lm', 'lx', 'a', 'yr', 'eV', 'pc', 'Jy', 'mag', 'R', 'bit', 'byte', 'G', 'barn' ] deprecated_bases = [] prefixes = [ 'y', 'z', 'a', 'f', 'p', 'n', 'u', 'm', 'c', 'd', '', 'da', 'h', 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y'] special_cases = {'dbyte': u.Unit('dbyte', 0.1*u.byte)} for base in bases + deprecated_bases: for prefix in prefixes: key = prefix + base if keyword.iskeyword(key): continue elif key in special_cases: names[key] = special_cases[key] else: names[key] = getattr(u, key) for base in deprecated_bases: for prefix in prefixes: deprecated_names.add(prefix + base) simple_units = [ 'deg', 'arcmin', 'arcsec', 'mas', 'min', 'h', 'd', 'Ry', 'solMass', 'u', 'solLum', 'solRad', 'AU', 'lyr', 'count', 'ct', 'photon', 'ph', 'pixel', 'pix', 'D', 'Sun', 'chan', 'bin', 'voxel', 'adu', 'beam', 'erg', 'Angstrom', 'angstrom' ] deprecated_units = [] for unit in simple_units + deprecated_units: names[unit] = getattr(u, unit) for unit in deprecated_units: deprecated_names.add(unit) return names, deprecated_names, [] @classmethod def _validate_unit(cls, unit, detailed_exception=True): if unit not in cls._units: if detailed_exception: raise ValueError( "Unit '{}' not supported by the FITS standard. {}".format( unit, utils.did_you_mean_units( unit, cls._units, cls._deprecated_units, cls._to_decomposed_alternative))) else: raise ValueError() if unit in cls._deprecated_units: utils.unit_deprecation_warning( unit, cls._units[unit], 'FITS', cls._to_decomposed_alternative) @classmethod def _parse_unit(cls, unit, detailed_exception=True): cls._validate_unit(unit) return cls._units[unit] @classmethod def _get_unit_name(cls, unit): name = unit.get_format_name('fits') cls._validate_unit(name) return name
[docs] @classmethod def to_string(cls, unit): # Remove units that aren't known to the format unit = utils.decompose_to_known_units(unit, cls._get_unit_name) parts = [] if isinstance(unit, core.CompositeUnit): base = np.log10(unit.scale) if base % 1.0 != 0.0: raise core.UnitScaleError( "The FITS unit format is not able to represent scales " "that are not powers of 10. Multiply your data by " "{:e}.".format(unit.scale)) elif unit.scale != 1.0: parts.append('10**{}'.format(int(base))) pairs = list(zip(unit.bases, unit.powers)) if len(pairs): pairs.sort(key=operator.itemgetter(1), reverse=True) parts.append(cls._format_unit_list(pairs)) s = ' '.join(parts) elif isinstance(unit, core.NamedUnit): s = cls._get_unit_name(unit) return s
@classmethod def _to_decomposed_alternative(cls, unit): try: s = cls.to_string(unit) except core.UnitScaleError: scale = unit.scale unit = copy.copy(unit) unit._scale = 1.0 return '{} (with data multiplied by {})'.format( cls.to_string(unit), scale) return s
[docs] @classmethod def parse(cls, s, debug=False): result = super().parse(s, debug) if hasattr(result, 'function_unit'): raise ValueError("Function units are not yet supported for " "FITS units.") return result