Coverage for python/lsst/daf/butler/core/time_utils.py : 35%

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1# This file is part of daf_butler.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <http://www.gnu.org/licenses/>.
21from __future__ import annotations
23__all__ = ("astropy_to_nsec", "nsec_to_astropy", "times_equal")
25import logging
26from typing import Any
27import warnings
29import astropy.time
30import astropy.utils.exceptions
31import yaml
33# As of astropy 4.2, the erfa interface is shipped independently and
34# ErfaWarning is no longer an AstropyWarning
35try:
36 import erfa
37except ImportError:
38 erfa = None
40# These constants can be used by client code.
41# EPOCH is used to construct times as read from database, its precision is
42# used by all those timestamps, set it to 1 microsecond.
43EPOCH = astropy.time.Time("1970-01-01 00:00:00", format="iso", scale="tai", precision=6)
44"""Epoch for calculating time delta, this is the minimum time that can be
45stored in the database.
46"""
48MAX_TIME = astropy.time.Time("2100-01-01 00:00:00", format="iso", scale="tai")
49"""Maximum time value that we can store. Assuming 64-bit integer field we
50can actually store higher values but we intentionally limit it to arbitrary
51but reasonably high value. Note that this value will be stored in registry
52database for eternity, so it should not be changed without proper
53consideration.
54"""
56# number of nanosecons in a day
57_NSEC_PER_DAY = 1_000_000_000 * 24 * 3600
59_LOG = logging.getLogger(__name__)
62def astropy_to_nsec(astropy_time: astropy.time.Time) -> int:
63 """Convert astropy time to nanoseconds since epoch.
65 Input time is converted to TAI scale before conversion to
66 nanoseconds.
68 Parameters
69 ----------
70 astropy_time : `astropy.time.Time`
71 Time to be converted.
73 Returns
74 -------
75 time_nsec : `int`
76 Nanoseconds since epoch.
78 Note
79 ----
80 Only the limited range of input times is supported by this method as it
81 is defined useful in the context of Butler and Registry. If input time is
82 earlier than epoch time then this method returns 0. If input time comes
83 after the max. time then it returns number corresponding to max. time.
84 """
85 # sometimes comparison produces warnings if input value is in UTC
86 # scale, transform it to TAI before doing anything but also trap
87 # warnings in case we are dealing with simulated data from the future
88 with warnings.catch_warnings():
89 warnings.simplefilter("ignore", category=astropy.utils.exceptions.AstropyWarning)
90 if erfa is not None:
91 warnings.simplefilter("ignore", category=erfa.ErfaWarning)
92 value = astropy_time.tai
93 # anything before epoch or after MAX_TIME is truncated
94 if value < EPOCH:
95 _LOG.warning("'%s' is earlier than epoch time '%s', epoch time will be used instead",
96 astropy_time, EPOCH)
97 value = EPOCH
98 elif value > MAX_TIME:
99 _LOG.warning("'%s' is later than max. time '%s', max. time time will be used instead",
100 value, MAX_TIME)
101 value = MAX_TIME
103 delta = value - EPOCH
104 # Special care needed to preserve nanosecond precision.
105 # Usually jd1 has no fractional part but just in case.
106 jd1, extra_jd2 = divmod(delta.jd1, 1)
107 value = int(jd1) * _NSEC_PER_DAY + int(round((delta.jd2 + extra_jd2)*_NSEC_PER_DAY))
108 return value
111def nsec_to_astropy(time_nsec: int) -> astropy.time.Time:
112 """Convert nanoseconds since epoch to astropy time.
114 Parameters
115 ----------
116 time_nsec : `int`
117 Nanoseconds since epoch.
119 Returns
120 -------
121 astropy_time : `astropy.time.Time`
122 Time to be converted.
124 Note
125 ----
126 Usually the input time for this method is the number returned from
127 `astropy_to_nsec` which has a limited range. This method does not check
128 that the number falls in the supported range and can produce output
129 time that is outside of that range.
130 """
131 jd1, jd2 = divmod(time_nsec, _NSEC_PER_DAY)
132 delta = astropy.time.TimeDelta(float(jd1), float(jd2)/_NSEC_PER_DAY, format="jd", scale="tai")
133 value = EPOCH + delta
134 return value
137def times_equal(time1: astropy.time.Time,
138 time2: astropy.time.Time,
139 precision_nsec: float = 1.0) -> bool:
140 """Check that times are equal within specified precision.
142 Parameters
143 ----------
144 time1, time2 : `astropy.time.Time`
145 Times to compare.
146 precision_nsec : `float`, optional
147 Precision to use for comparison in nanoseconds, default is one
148 nanosecond which is larger that round-trip error for conversion
149 to/from integer nanoseconds.
150 """
151 # To compare we need them in common scale, for simplicity just
152 # bring them both to TAI scale
153 # Hide any warnings from this conversion since they are not relevant
154 # to the equality
155 with warnings.catch_warnings():
156 warnings.simplefilter("ignore", category=astropy.utils.exceptions.AstropyWarning)
157 if erfa is not None:
158 warnings.simplefilter("ignore", category=erfa.ErfaWarning)
159 time1 = time1.tai
160 time2 = time2.tai
161 delta = (time2.jd1 - time1.jd1) + (time2.jd2 - time1.jd2)
162 delta *= _NSEC_PER_DAY
163 return abs(delta) < precision_nsec
166class _AstropyTimeToYAML:
167 """Handle conversion of astropy Time to/from YAML representation.
169 This class defines methods that convert astropy Time instances to or from
170 YAML representation. On output it converts time to string ISO format in
171 TAI scale with maximum precision defining special YAML tag for it. On
172 input it does inverse transformation. The methods need to be registered
173 with YAML dumper and loader classes.
175 Notes
176 -----
177 Python ``yaml`` module defines special helper base class ``YAMLObject``
178 that provides similar functionality but its use is complicated by the need
179 to convert ``Time`` instances to instances of ``YAMLObject`` sub-class
180 before saving them to YAML. This class avoids this intermediate step but
181 it requires separate regisration step.
182 """
184 yaml_tag = "!butler_time/tai/iso" # YAML tag name for Time class
186 @classmethod
187 def to_yaml(cls, dumper: yaml.Dumper, data: astropy.time.Time) -> Any:
188 """Convert astropy Time object into YAML format.
190 Parameters
191 ----------
192 dumper : `yaml.Dumper`
193 YAML dumper instance.
194 data : `astropy.time.Time`
195 Data to be converted.
196 """
197 if data is not None:
198 # we store time in ISO format but we need full nanosecond
199 # precision so we have to construct intermediate instance to make
200 # sure its precision is set correctly.
201 data = astropy.time.Time(data.tai, precision=9)
202 data = data.to_value("iso")
203 return dumper.represent_scalar(cls.yaml_tag, data)
205 @classmethod
206 def from_yaml(cls, loader: yaml.SafeLoader, node: yaml.ScalarNode) -> astropy.time.Time:
207 """Convert YAML node into astropy time
209 Parameters
210 ----------
211 loader : `yaml.SafeLoader`
212 Instance of YAML loader class.
213 node : `yaml.ScalarNode`
214 YAML node.
216 Returns
217 -------
218 time : `astropy.time.Time`
219 Time instance, can be ``None``.
220 """
221 if node.value is not None:
222 return astropy.time.Time(node.value, format="iso", scale="tai")
225# Register Time -> YAML conversion method with Dumper class
226yaml.Dumper.add_representer(astropy.time.Time, _AstropyTimeToYAML.to_yaml)
228# Register YAML -> Time conversion method with Loader, for our use case we
229# only need SafeLoader.
230yaml.SafeLoader.add_constructor(_AstropyTimeToYAML.yaml_tag, _AstropyTimeToYAML.from_yaml)