88 lines
3.1 KiB
Python
88 lines
3.1 KiB
Python
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# Copyright 2020 Google Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Parse RFC3339 date strings"""
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from datetime import datetime, timezone
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import re
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def parse_to_epoch(datestr):
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"""Parse an RFC3339 date string and return the number of seconds since the
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epoch (as a float).
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In particular, this method is meant to parse the strings returned by the
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JSON mapping of protobuf google.protobuf.timestamp.Timestamp instances:
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https://github.com/protocolbuffers/protobuf/blob/4cf5bfee9546101d98754d23ff378ff718ba8438/src/google/protobuf/timestamp.proto#L99
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This method has microsecond precision; nanoseconds will be truncated.
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Args:
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datestr: A string in RFC3339 format.
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Returns:
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Float: The number of seconds since the Unix epoch.
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Raises:
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ValueError: Raised if the `datestr` is not a valid RFC3339 date string.
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"""
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return _parse_to_datetime(datestr).timestamp()
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def _parse_to_datetime(datestr):
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"""Parse an RFC3339 date string and return a python datetime instance.
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Args:
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datestr: A string in RFC3339 format.
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Returns:
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datetime: The corresponding `datetime` (with timezone information).
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Raises:
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ValueError: Raised if the `datestr` is not a valid RFC3339 date string.
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"""
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# If more than 6 digits appear in the fractional seconds position, truncate
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# to just the most significant 6. (i.e. we only have microsecond precision;
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# nanos are truncated.)
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datestr_modified = re.sub(r'(\.\d{6})\d*', r'\1', datestr)
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# This format is the one we actually expect to occur from our backend. The
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# others are only present because the spec says we *should* accept them.
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try:
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return datetime.strptime(
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datestr_modified, '%Y-%m-%dT%H:%M:%S.%fZ'
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).replace(tzinfo=timezone.utc)
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except ValueError:
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pass
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try:
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return datetime.strptime(
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datestr_modified, '%Y-%m-%dT%H:%M:%SZ'
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).replace(tzinfo=timezone.utc)
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except ValueError:
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pass
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# Note: %z parses timezone offsets, but requires the timezone offset *not*
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# include a separating ':'. As of python 3.7, this was relaxed.
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# TODO(rsgowman): Once python3.7 becomes our floor, we can drop the regex
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# replacement.
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datestr_modified = re.sub(r'(\d\d):(\d\d)$', r'\1\2', datestr_modified)
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try:
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return datetime.strptime(datestr_modified, '%Y-%m-%dT%H:%M:%S.%f%z')
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except ValueError:
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pass
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try:
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return datetime.strptime(datestr_modified, '%Y-%m-%dT%H:%M:%S%z')
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except ValueError:
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pass
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raise ValueError('time data {0} does not match RFC3339 format'.format(datestr))
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