Source code for rubin_scheduler.scheduler.features.conditions

__all__ = ("Conditions",)

import functools
import warnings
from inspect import signature
from io import StringIO

import healpy as hp
import numpy as np
import pandas as pd

from rubin_scheduler.scheduler.utils import match_hp_resolution, smallest_signed_angle
from rubin_scheduler.utils import (
    DEFAULT_NSIDE,
    Site,
    _angular_separation,
    _approx_altaz2pa,
    _approx_ra_dec2_alt_az,
    _hpid2_ra_dec,
    calc_lmst,
    m5_flat_sed,
)


[docs] class Conditions: """Holds telemetry information, keeping calculated values in sync for `self.mjd` (such as ra/dec mappings to alt/az). Incoming values have setters to keep values in sync. Healpix maps are set to the expected (`self.nside`) resolution. Unless otherwise noted, all values are assumed to be valid at the time given by `self.mjd`. Parameters ---------- nside : `int`, optional The healpixel nside to set the resolution of attributes. Default of None will use `rubin_scheduler.scheduler.utils.set_default_nside`. site : str ('LSST') A site name used to create a sims.utils.Site object. For looking up observatory parameters like latitude and longitude. exptime : `float`, optional The exposure time (seconds) to assume when computing the 5-sigma limiting depth maps stored in Conditions. These maps are used by basis functions, but are not used to calculate expected observation m5 values (such as when exposure time varies). Default 30 seconds. mjd : `float`, optional The current MJD. Default of None is fine on init - will be updated by telemetry stream. """ global_maps = set(["ra", "dec", "slewtime", "airmass", "zeros_map", "nan_map"]) by_band_maps = set(["skybrightness", "fwhm_eff", "m5_depth"]) def __init__( self, nside=DEFAULT_NSIDE, site="LSST", exptime=30.0, mjd=None, ): """ Attributes (Set on init) ----------- nside : `int` Healpix resolution. All maps are set to this reslution. site : rubin_scheduler.Site object ('LSST') Contains static site-specific data (lat, lon, altitude, etc). Defaults to 'LSST'. ra : `np.ndarray`, (N,) A healpix array with the RA of each healpixel center (radians). Automatically generated. dec : `np.ndarray`, (N,) A healpix array with the Dec of each healpixel center (radians). Automatically generated. Attributes (to be set by user/telemetry stream/scheduler) ------------------------------------------- mjd : `float` Modified Julian Date (days). bulk_cloud : `float` The fraction of sky covered by clouds. (In the future might update to transparency map) cloud_map : `np.ndarray`, (N,) XXX--to be done. HEALpix array with cloudy pixels set to NaN. slewtime : `np.ndarray`, (N,) Healpix showing the slewtime to each healpixel center (seconds) current_filter : `str` The name of the current filter. (expect one of u, g, r, i, z, y). mounted_filters : `list` [`str`] The filters that are currently mounted and thus available (expect 5 of u, g, r, i, z, y for LSSTCam). night : `int` The current night number (days). Probably starts at 1. skybrightness : `dict` {`str: `np.ndarray`, (N,)} Dictionary keyed by filter name. Values are healpix arrays with the sky brightness at each healpix center (mag/acsec^2) fwhm_eff : `dict` {`str: `np.ndarray`, (N,)} Dictionary keyed by filtername. Values are the effective seeing FWHM at each healpix center (arcseconds) moon_alt : `float` The altitude of the Moon (radians) moon_az : `float` The Azimuth of the moon (radians) moon_ra : `float` RA of the moon (radians) moon_dec : `float` Declination of the moon (radians) moon_phase : `float` The Phase of the moon. (percent, 0=new moon, 100=full moon) sun_alt : `float` The altitude of the sun (radians). sun_az : `float` The Azimuth of the sun (radians). sun_ra : `float` The RA of the sun (radians). sun_dec : `float` The Dec of the sun (radians). tel_ra : `float` The current telescope RA pointing (radians). tel_dec : `float` The current telescope Declination (radians). tel_alt : `float` The current telescope altitude (radians). tel_az : `float` The current telescope azimuth (radians). cumulative_azimuth_rad : `float` The cumulative telescope azimuth (radians). Used for tracking cable wrap. wind_speed : `float` Wind speed (m/s). wind_direction : `float` Direction from which the wind originates. A direction of 0.0 degrees means the wind originates from the north and 90.0 degrees from the east (radians). sunset : `float` The MJD of sunset that starts the current night. Note MJDs of sunset, moonset, twilight times, etc are from interpolations. This means the sun may actually be slightly above/below the horizon at the given sunset time. sun_n12_setting : `float` The MJD of when the sun is at -12 degrees altitude and setting during the current night. From interpolation. sun_n18_setting : `float` The MJD when the sun is at -18 degrees altitude and setting during the current night. From interpolation. sun_n18_rising : `float` The MJD when the sun is at -18 degrees altitude and rising during the current night. From interpolation. sun_n12_rising : `float` The MJD when the sun is at -12 degrees altitude and rising during the current night. From interpolation. sunrise : `float` The MJD of sunrise during the current night. From interpolation moonrise : `float` The MJD of moonrise during the current night. From interpolation. moonset : `float` The MJD of moon set during the current night. From interpolation. moon_phase_sunset : `float` The phase of the moon (0-100 illuminated) at sunset. Useful for setting which filters should be loaded. targets_of_opportunity : `list` [`rubin_scheduler.scheduler.targetoO`] targetoO objects. planet_positions : `dict` {`str`: `float`} Dictionary of planet name and coordinate e.g., 'venus_RA', 'mars_dec' scheduled_observations : `np.ndarray`, (M,) A list of MJD times when there are scheduled observations. Defaults to empty array. sky_az_limits : `list` [[`float`, `float`]] A list of lists giving valid azimuth ranges. e.g., [0, 2*np.pi] would mean all azimuth values are valid, while [[0, np.pi/2], [3*np.pi/2, 2*np.pi]] would mean anywhere in the south is invalid. Radians. sky_alt_limits : `list` [[`float`, `float`]] A list of lists giving valid altitude ranges. Radians. tel_az_limits : `list` [`float`, `float`] A simple two-element list giving the valid azimuth ranges for the telescope movement. Radians. tel_alt_limits : `list` [`float`, `float`] A simple two-element list giving the valid altitude ranges for the telescope movement. Radians Attributes (calculated on demand and cached) ------------------------------------------ alt : `np.ndarray`, (N,) Altitude of each healpixel (radians). Recalculated if mjd is updated. Uses fast approximate equation for converting RA,Dec to alt,az. az : `np.ndarray`, (N,) Azimuth of each healpixel (radians). Recalculated if mjd is updated. Uses fast approximate equation for converting RA,Dec to alt,az. airmass : `np.ndarray`, (N,) A healpix map with the airmass value of each healpixel. (unitless) pa : `np.ndarray`, (N,) The parallactic angle of each healpixel (radians). Recalculated if mjd is updated. Based on the fast approximate alt,az values. lmst : `float` The local mean sidereal time (hours). Updates is mjd is changed. m5_depth : `dict` {`str: `np.ndarray`, (N,)} the 5-sigma limiting depth healpix maps, keyed by filtername (mags). Will be recalculated if the skybrightness, seeing, or airmass are updated. HA : `np.ndarray`, (N,) Healpix map of the hour angle of each healpixel (radians). Runs from 0 to 2pi. az_to_sun : `np.ndarray`, (N,) Healpix map of the azimuthal distance to the sun for each healpixel (radians) az_to_anitsun : `np.ndarray`, (N,) Healpix map of the azimuthal distance to the anit-sun for each healpixel (radians) solar_elongation : `np.ndarray`, (N,) Healpix map of the solar elongation (angular distance to the sun) for each healpixel (radians) Attributes (set by the scheduler) ------------------------------- queue : `list` [`observation` objects] The current queue of observations core_scheduler is waiting to execute. """ self.nside = nside # The RA, Dec grid we are using hpids = np.arange(hp.nside2npix(self.nside)) self.ra, self.dec = _hpid2_ra_dec(self.nside, hpids) self.site = Site(site) self.exptime = exptime # Generate an empty map so we can copy when we need a new map self.zeros_map = np.zeros(hp.nside2npix(self.nside), dtype=float) self.nan_map = np.zeros(hp.nside2npix(self.nside), dtype=float) self.nan_map.fill(np.nan) # Set other attributes to Nones self._init_attributes() self.mjd = mjd def _init_attributes(self): """Initialize or clear all the attributes""" # Modified Julian Date (day) self._mjd = None # Altitude and azimuth. Dict with degrees and radians self._alt = None self._az = None self._pa = None # The cloud level. Fraction, but could upgrade to transparency map self.clouds = None self._slewtime = None self.current_filter = None self.mounted_filters = None self.night = None self._lmst = None # Should be a dict with filtername keys self._skybrightness = {} self._fwhm_eff = {} self._m5_depth = None self._airmass = None self.wind_speed = None self.wind_direction = None # Upcoming scheduled observations self.scheduled_observations = np.array([], dtype=float) # Attribute to hold the current observing queue self.queue = None # Moon self.moon_alt = None self.moon_az = None self.moon_ra = None self.moon_dec = None self.moon_phase = None # Sun self.sun_alt = None self.sun_az = None self.sun_ra = None self.sun_dec = None # Almanac information self.sunset = None self.sun_n12_setting = None self.sun_n18_setting = None self.sun_n18_rising = None self.sun_n12_rising = None self.sunrise = None self.moonrise = None self.moonset = None self.moon_phase_sunset = None self.planet_positions = None # Current telescope pointing self.tel_ra = None self.tel_dec = None self.tel_alt = None self.tel_az = None self.cumulative_azimuth_rad = None # Sky coverage limits. # These should be in radians. self.sky_az_limits = None self.sky_alt_limits = None # Kinematic model (real slew) limits. self.tel_alt_limits = None self.tel_az_limits = None # Full sky cloud map self._cloud_map = None self._HA = None # XXX--document self.bulk_cloud = None self.rot_tel_pos = None self.targets_of_opportunity = None # Potential attributes that get computed self._solar_elongation = None self._az_to_sun = None self._az_to_antisun = None @property def lmst(self): if self._lmst is None: self._lmst = calc_lmst(self.mjd, self.site.longitude_rad) return self._lmst @lmst.setter def lmst(self, value): self._lmst = value self._HA = None @property def HA(self): if self._HA is None: self.calc_ha() return self._HA def calc_ha(self): self._HA = np.radians(self.lmst * 360.0 / 24.0) - self.ra self._HA[np.where(self._HA < 0)] += 2.0 * np.pi @property def cloud_map(self): return self._cloud_map @cloud_map.setter def cloud_map(self, value): self._cloud_map = match_hp_resolution(value, nside_out=self.nside) @property def slewtime(self): return self._slewtime @slewtime.setter def slewtime(self, value): # Using 0 for start of night if np.size(value) == 1: self._slewtime = value else: self._slewtime = match_hp_resolution(value, nside_out=self.nside) @property def airmass(self): if self._airmass is None: self.calc_airmass() return self._airmass def calc_airmass(self): self._airmass = np.zeros(self._alt.size, dtype=float) self._airmass.fill(np.nan) alt_limit = self.tel_alt_limits if alt_limit is None: alt_limit = 0 else: alt_limit = np.min(alt_limit) good = np.where(self._alt > alt_limit) self._airmass[good] = 1.0 / np.cos(np.pi / 2.0 - self._alt[good]) @property def pa(self): if self._pa is None: self.calc_pa() return self._pa def calc_pa(self): self._pa = _approx_altaz2pa(self.alt, self.az, self.site.latitude_rad) @property def alt(self): if self._alt is None: self.calc_alt_az() return self._alt @property def az(self): if self._az is None: self.calc_alt_az() return self._az def calc_alt_az(self): self._alt, self._az = _approx_ra_dec2_alt_az( self.ra, self.dec, self.site.latitude_rad, self.site.longitude_rad, self._mjd, )
[docs] @functools.lru_cache(maxsize=10) def future_alt_az(self, mjd): """Compute the altitude and azimuth for a future time. Returns ------- altitude : `np.array` The altutude of each healpix at MJD (radians) azimuth : : `np.array` The azimuth of each healpix at MJD (radians) """ alt, az = _approx_ra_dec2_alt_az( self.ra, self.dec, self.site.latitude_rad, self.site.longitude_rad, mjd, ) return alt, az
@property def mjd(self): return self._mjd @mjd.setter def mjd(self, value): # If MJD is changed, everything else is no longer valid, so re-init if self.mjd is not None: warnings.warn("Changing MJD and resetting all attributes.") self._init_attributes() self._mjd = value @property def skybrightness(self): return self._skybrightness @skybrightness.setter def skybrightness(self, indict): for key in indict: self._skybrightness[key] = match_hp_resolution(indict[key], nside_out=self.nside) # If sky brightness changes, need to recalc M5 depth. self._m5_depth = None @property def fwhm_eff(self): return self._fwhm_eff @fwhm_eff.setter def fwhm_eff(self, indict): for key in indict: self._fwhm_eff[key] = match_hp_resolution(indict[key], nside_out=self.nside) self._m5_depth = None @property def m5_depth(self): if self._m5_depth is None: self.calc_m5_depth() return self._m5_depth def calc_m5_depth(self): self._m5_depth = {} for filtername in self._skybrightness: good = ~np.isnan(self._skybrightness[filtername]) self._m5_depth[filtername] = self.nan_map.copy() self._m5_depth[filtername][good] = m5_flat_sed( filtername, self._skybrightness[filtername][good], self._fwhm_eff[filtername][good], self.exptime, self._airmass[good], ) def calc_solar_elongation(self): self._solar_elongation = _angular_separation(self.ra, self.dec, self.sun_ra, self.sun_dec) @property def solar_elongation(self): if self._solar_elongation is None: self.calc_solar_elongation() return self._solar_elongation def calc_az_to_sun(self): self._az_to_sun = smallest_signed_angle(self.ra, self.sun_ra) def calc_az_to_antisun(self): self._az_to_antisun = smallest_signed_angle(self.ra + np.pi, self.sun_ra) @property def az_to_sun(self): if self._az_to_sun is None: self.calc_az_to_sun() return self._az_to_sun @property def az_to_antisun(self): if self._az_to_antisun is None: self.calc_az_to_antisun() return self._az_to_antisun
[docs] def set_auxtel_info( self, mjd, slewtime, sun_n18_setting, sun_n18_rising, moon_alt, moon_az, tel_alt_limits, tel_az_limits, sky_alt_limits, sky_az_limits, wind_speed, wind_direction, **kwargs, ): """Method to set all the information we expect will be required by a standard auxtel scheduler. Extra attributes can be set via **kwargs. Parameters ---------- mjd : `float` Modified Julian Date (days). slewtime : `np.ndarray`, (N,) Healpix showing the slewtime to each healpixel center (seconds) moon_alt : `float` The altitude of the Moon (radians) moon_az : `float` The Azimuth of the moon (radians) wind_speed : `float` Wind speed (m/s). wind_direction : `float` Direction from which the wind originates. A direction of 0.0 degrees means the wind originates from the north and 90.0 degrees from the east (radians). sun_n18_setting : `float` The MJD when the sun is at -18 degrees altitude and setting during the current night. From interpolation. sun_n18_rising : `float` The MJD when the sun is at -18 degrees altitude and rising during the current night. From interpolation. sky_az_limits : `list` [[`float`, `float`]] A list of lists giving valid azimuth ranges. e.g., [0, 2*np.pi] would mean all azimuth values are valid, while [[0, np.pi/2], [3*np.pi/2, 2*np.pi]] would mean anywhere in the south is invalid. Radians. sky_alt_limits : `list` [[`float`, `float`]] A list of lists giving valid altitude ranges. Radians. tel_az_limits : `list` [`float`, `float`] A simple two-element list giving the valid azimuth ranges for the telescope movement. Radians. tel_alt_limits : `list` [`float`, `float`] A simple two-element list giving the valid altitude ranges for the telescope movement. Radians """ self._init_attributes() auxtel_args = signature(self.set_auxtel_info) loc = locals() for key in auxtel_args.parameters.keys(): setattr(self, key, loc[key]) potential_attrs = dir(self) for key in kwargs: if key not in potential_attrs: warnings.warn("Setting unexpected Conditions attribute %s" % key) setattr(self, key, kwargs[key])
[docs] def set_maintel_info( self, mjd, slewtime, current_filter, mounted_filters, night, skybrightness, fwhm_eff, moon_alt, moon_az, moon_ra, moon_dec, moon_phase, sun_alt, sun_az, sun_ra, sun_dec, tel_ra, tel_dec, tel_alt, tel_az, wind_speed, wind_direction, sun_n12_setting, sun_n12_rising, sun_n18_setting, sun_n18_rising, moonrise, moonset, planet_positions, tel_alt_limits, tel_az_limits, sky_alt_limits, sky_az_limits, **kwargs, ): """Method to set all the information we expect will be required by a standard maintel scheduler. Extra attributes can be set via **kwargs. mjd : `float` Modified Julian Date (days). slewtime : `np.ndarray`, (N,) Healpix showing the slewtime to each healpixel center (seconds) current_filter : `str` The name of the current filter. (expect one of u, g, r, i, z, y). mounted_filters : `list` [`str`] The filters that are currently mounted and thus available (expect 5 of u, g, r, i, z, y for LSSTCam). night : `int` The current night number (days). Probably starts at 1. skybrightness : `dict` {`str: `np.ndarray`, (N,)} Dictionary keyed by filter name. Values are healpix arrays with the sky brightness at each healpix center (mag/acsec^2) fwhm_eff : `dict` {`str: `np.ndarray`, (N,)} Dictionary keyed by filtername. Values are the effective seeing FWHM at each healpix center (arcseconds) moon_alt : `float` The altitude of the Moon (radians) moon_az : `float` The Azimuth of the moon (radians) moon_ra : `float` RA of the moon (radians) moon_dec : `float` Declination of the moon (radians) moon_phase : `float` The Phase of the moon. (percent, 0=new moon, 100=full moon) sun_alt : `float` The altitude of the sun (radians). sun_az : `float` The Azimuth of the sun (radians). sun_ra : `float` The RA of the sun (radians). sun_dec : `float` The Dec of the sun (radians). tel_ra : `float` The current telescope RA pointing (radians). tel_dec : `float` The current telescope Declination (radians). tel_alt : `float` The current telescope altitude (radians). tel_az : `float` The current telescope azimuth (radians). wind_speed : `float` Wind speed (m/s). wind_direction : `float` Direction from which the wind originates. A direction of 0.0 degrees means the wind originates from the north and 90.0 degrees from the east (radians). sun_n12_setting : `float` The MJD of when the sun is at -12 degrees altitude and setting during the current night. From interpolation. sun_n18_setting : `float` The MJD when the sun is at -18 degrees altitude and setting during the current night. From interpolation. sun_n18_rising : `float` The MJD when the sun is at -18 degrees altitude and rising during the current night. From interpolation. sun_n12_rising : `float` The MJD when the sun is at -12 degrees altitude and rising during the current night. From interpolation. moonrise : `float` The MJD of moonrise during the current night. From interpolation. moonset : `float` The MJD of moon set during the current night. From interpolation. moon_phase_sunset : `float` The phase of the moon (0-100 illuminated) at sunset. Useful for setting which filters should be loaded. targets_of_opportunity : `list` [`rubin_scheduler.scheduler.targetoO`] targetoO objects. planet_positions : `dict` {`str`: `float`} Dictionary of planet name and coordinate e.g., 'venus_RA', 'mars_dec' sky_az_limits : `list` [[`float`, `float`]] A list of lists giving valid azimuth ranges. e.g., [0, 2*np.pi] would mean all azimuth values are valid, while [[0, np.pi/2], [3*np.pi/2, 2*np.pi]] would mean anywhere in the south is invalid. Radians. sky_alt_limits : `list` [[`float`, `float`]] A list of lists giving valid altitude ranges. Radians. tel_az_limits : `list` [`float`, `float`] A simple two-element list giving the valid azimuth ranges for the telescope movement. Radians. tel_alt_limits : `list` [`float`, `float`] A simple two-element list giving the valid altitude ranges for the telescope movement. Radians """ self._init_attributes() maintel_args = signature(self.set_maintel_info) loc = locals() for key in maintel_args.parameters.keys(): setattr(self, key, loc[key]) potential_attrs = dir(self) for key in kwargs: if key not in potential_attrs: warnings.warn("Setting unexpected Conditions attribute %s" % key) setattr(self, key, kwargs[key])
[docs] def set_attrs(self, **kwargs): """Convience function for setting lots of attributes at once. See __init__ docstring for full list of potential attributes.""" potential_attrs = dir(self) for key in kwargs: if key not in potential_attrs: warnings.warn("Setting unexpected Conditions attribute %s" % key) setattr(self, key, kwargs[key])
def __repr__(self): return f"<{self.__class__.__name__} mjd='{self.mjd}' at {hex(id(self))}>" def __str__(self): # If dependencies of to_markdown are not installed, fall back on repr try: pd.DataFrame().to_markdown() except ImportError: return repr(self) if self.mjd is None: # Many elements of the pretty str representation rely on # the time beging set. If it is not, just return the ugly form. return repr(self) output = StringIO() print(f"{self.__class__.__qualname__} at {hex(id(self))}", file=output) print("============================", file=output) print("nside: ", self.nside, " ", file=output) print("site: ", self.site.name, " ", file=output) print("exptime: ", self.exptime, " ", file=output) print("lmst: ", self.lmst, " ", file=output) print("clouds: ", self.clouds, " ", file=output) print("current_filter: ", self.current_filter, " ", file=output) print("mounted_filters: ", self.mounted_filters, " ", file=output) print("night: ", self.night, " ", file=output) print("wind_speed: ", self.wind_speed, " ", file=output) print("wind_direction: ", self.wind_direction, " ", file=output) print( "len(scheduled_observations): ", len(self.scheduled_observations), " ", file=output, ) print( "len(queue): ", None if self.queue is None else len(self.queue), " ", file=output, ) print("moonPhase: ", self.moon_phase, " ", file=output) print("bulk_cloud: ", self.bulk_cloud, " ", file=output) print("targets_of_opportunity: ", self.targets_of_opportunity, " ", file=output) print("cumulative_azimuth_rad: ", self.cumulative_azimuth_rad, " ", file=output) positions = [ { "name": "sun", "alt": self.sun_alt, "az": self.sun_az, "RA": self.sun_ra, "decl": self.sun_dec, } ] positions.append( { "name": "moon", "alt": self.moon_alt, "az": self.moon_az, "RA": self.moon_ra, "decl": self.moon_dec, } ) for planet_name in ("venus", "mars", "jupiter", "saturn"): positions.append( { "name": planet_name, "RA": float(np.max(self.planet_positions[planet_name + "_RA"])), "decl": float(np.max(self.planet_positions[planet_name + "_dec"])), } ) positions.append( { "name": "telescope", "alt": np.max(self.tel_alt), "az": np.max(self.tel_az), "RA": np.max(self.tel_ra), "decl": np.max(self.tel_dec), "rot": np.max(self.rot_tel_pos), } ) positions = pd.DataFrame(positions).set_index("name") print(file=output) print("Positions (radians)", file=output) print("-------------------", file=output) print(positions.to_markdown(), file=output) positions_deg = np.degrees(positions) print(file=output) print("Positions (degrees)", file=output) print("-------------------", file=output) print(positions_deg.to_markdown(), file=output) events = ( "mjd", "sunset", "sun_n12_setting", "sun_n18_setting", "sun_n18_rising", "sun_n12_rising", "sunrise", "moonrise", "moonset", "sun_0_setting", "sun_0_rising", ) event_rows = [] for event in events: try: mjd = getattr(self, event) time = pd.to_datetime(float(mjd) + 2400000.5, unit="D", origin="julian") event_rows.append({"event": event, "MJD": mjd, "date": time}) except AttributeError: pass event_df = pd.DataFrame(event_rows).set_index("event").sort_values(by="MJD") print("", file=output) print("Events", file=output) print("------", file=output) print(event_df.to_markdown(), file=output) map_stats = [] for map_name in self.global_maps - set(["zeros_map", "nan_map"]): try: values = getattr(self, map_name) map_stats.append( { "map": map_name, "nside": hp.npix2nside(len(values)), "min": np.nanmin(values), "max": np.nanmax(values), "median": np.nanmedian(values), } ) except AttributeError: pass for base_map_name in self.by_band_maps: for band in "ugrizy": try: values = getattr(self, base_map_name)[band] map_name = f"{base_map_name}_{band}" map_stats.append( { "map": map_name, "nside": hp.npix2nside(len(values)), "min": np.nanmin(values), "max": np.nanmax(values), "median": np.nanmedian(values), } ) except AttributeError: pass maps_df = pd.DataFrame(map_stats).set_index("map") print("", file=output) print("Maps", file=output) print("----", file=output) print(maps_df.to_markdown(), file=output) result = output.getvalue() return result def _repr_markdown_(self): return str(self)