# 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 '{0}' not supported by the FITS standard. {1}".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 "
"{0:e}.".format(unit.scale))
elif unit.scale != 1.0:
parts.append('10**{0}'.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 '{0} (with data multiplied by {1})'.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