# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
Handles the "FITS" unit format.
"""
from __future__ import absolute_import, division, print_function, unicode_literals
import warnings
from . import generic
from . import utils
[docs]class Fits(generic.Generic):
"""
The FITS standard unit format.
This supports the format defined in the Units section of the `FITS
Standard <http://fits.gsfc.nasa.gov/fits_standard.html>`_.
"""
name = 'fits'
def __init__(self):
if not '_units' in Fits.__dict__:
Fits._units, Fits._deprecated_units = self._generate_unit_names()
if not '_parser' in Fits.__dict__:
Fits._parser = self._make_parser()
@staticmethod
def _generate_unit_names():
from ... import units as u
names = {}
deprecated_names = set()
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'
]
deprecated_bases = [
'G', 'barn'
]
prefixes = [
'y', 'z', 'a', 'f', 'p', 'n', 'u', 'm', 'c', 'd',
'', 'da', 'h', 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y']
for base in bases + deprecated_bases:
for prefix in prefixes:
key = prefix + base
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',
'photon', 'ph', 'pixel', 'pix', 'D', 'Sun', 'chan', 'bin',
'voxel', 'adu', 'beam'
]
deprecated_units = [
'erg', 'Angstrom'
]
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 _parse_unit(cls, s, loc, toks):
from astropy.extern import pyparsing as p
unit = toks[0]
if unit not in cls._units:
raise p.ParseException(
"Unit {0!r} not supported by the FITS standard.".format(unit))
if unit in cls._deprecated_units:
warnings.warn(
"The unit {0!r} has been deprecated in the FITS "
"standard.".format(unit),
DeprecationWarning)
return cls._units[unit]
def _get_unit_name(self, unit):
name = unit.get_format_name('fits')
if name not in self._units:
raise ValueError(
"Unit {0!r} is not part of the FITS standard".format(name))
if name in self._deprecated_units:
warnings.warn(
"The unit {0!r} has been deprecated in the FITS "
"standard.".format(name),
DeprecationWarning)
return name
[docs] def to_string(self, unit):
from .. import core
# Remove units that aren't known to the format
unit = utils.decompose_to_known_units(unit, self._get_unit_name)
if isinstance(unit, core.CompositeUnit):
if unit.scale != 1.0:
raise ValueError(
"The FITS unit format is not able to represent scale. "
"Multiply your data by {0:e}.".format(unit.scale))
pairs = zip(unit.bases, unit.powers)
pairs.sort(key=lambda x: x[1], reverse=True)
s = self._format_unit_list(pairs)
elif isinstance(unit, core.NamedUnit):
s = self._get_unit_name(unit)
return s