Source code for gammapy.utils.units

# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Units and Quantity related helper functions"""
import logging
import astropy.units as u

__all__ = ["standardise_unit", "unit_from_fits_image_hdu"]

log = logging.getLogger(__name__)

[docs]def standardise_unit(unit): """Standardise unit. Changes applied by this function: * Drop "photon" == "ph" from the unit * Drop "count" == "ct" from the unit Parameters ---------- unit : `~astropy.units.Unit` or str Any old unit Returns ------- unit : `~astropy.units.Unit` Shiny new, standardised unit Examples -------- >>> from gammapy.utils.units import standardise_unit >>> standardise_unit('ph cm-2 s-1') Unit("1 / (cm2 s)") >>> standardise_unit('ct cm-2 s-1') Unit("1 / (cm2 s)") >>> standardise_unit('cm-2 s-1') Unit("1 / (cm2 s)") """ unit = u.Unit(unit) bases, powers = [], [] for base, power in zip(unit.bases, unit.powers): if str(base) not in {"ph", "ct"}: bases.append(base) powers.append(power) return u.CompositeUnit(scale=unit.scale, bases=bases, powers=powers)
[docs]def unit_from_fits_image_hdu(header): """Read unit from a FITS image HDU. - The ``BUNIT`` key is used. - `astropy.units.Unit` is called. If the ``BUNIT`` value is invalid, a log warning is emitted and the empty unit is used. - `standardise_unit` is called """ unit = header.get("BUNIT", "") try: u.Unit(unit) except ValueError: log.warning(f"Invalid value BUNIT={unit!r} in FITS header. Setting empty unit.") unit = "" return standardise_unit(unit)