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'''
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This library is provided to allow standard python logging
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to output log data as JSON formatted strings
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'''
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import logging
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import json
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import re
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from datetime import date, datetime, time, tzinfo, timedelta
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import traceback
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import importlib
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from inspect import istraceback
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from collections import OrderedDict
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def _inject_req_id(record, *args, **kwargs):
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return record
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ExceptionAwareFormatter = logging.Formatter
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ZERO = timedelta(0)
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HOUR = timedelta(hours=1)
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class UTC(tzinfo):
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"""UTC"""
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def utcoffset(self, dt):
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return ZERO
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def tzname(self, dt):
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return "UTC"
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def dst(self, dt):
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return ZERO
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utc = UTC()
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# skip natural LogRecord attributes
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# http://docs.python.org/library/logging.html#logrecord-attributes
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RESERVED_ATTRS = (
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'args', 'asctime', 'created', 'exc_info', 'exc_text', 'filename',
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'funcName', 'levelname', 'levelno', 'lineno', 'module',
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'msecs', 'message', 'msg', 'name', 'pathname', 'process',
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'processName', 'relativeCreated', 'stack_info', 'thread', 'threadName')
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def merge_record_extra(record, target, reserved):
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"""
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Merges extra attributes from LogRecord object into target dictionary
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:param record: logging.LogRecord
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:param target: dict to update
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:param reserved: dict or list with reserved keys to skip
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"""
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for key, value in record.__dict__.items():
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# this allows to have numeric keys
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if (key not in reserved
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and not (hasattr(key, "startswith")
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and key.startswith('_'))):
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target[key] = value
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return target
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class JsonEncoder(json.JSONEncoder):
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"""
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A custom encoder extending the default JSONEncoder
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"""
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def default(self, obj):
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if isinstance(obj, (date, datetime, time)):
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return self.format_datetime_obj(obj)
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elif istraceback(obj):
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return ''.join(traceback.format_tb(obj)).strip()
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elif type(obj) == Exception \
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or isinstance(obj, Exception) \
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or type(obj) == type:
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return str(obj)
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try:
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return super(JsonEncoder, self).default(obj)
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except TypeError:
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try:
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return str(obj)
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except Exception:
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return None
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def format_datetime_obj(self, obj):
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return obj.isoformat()
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class JsonFormatter(ExceptionAwareFormatter):
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"""
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A custom formatter to format logging records as json strings.
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Extra values will be formatted as str() if not supported by
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json default encoder
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"""
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def __init__(self, *args, **kwargs):
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"""
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:param json_default: a function for encoding non-standard objects
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as outlined in http://docs.python.org/2/library/json.html
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:param json_encoder: optional custom encoder
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:param json_serializer: a :meth:`json.dumps`-compatible callable
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that will be used to serialize the log record.
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:param json_indent: an optional :meth:`json.dumps`-compatible numeric value
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that will be used to customize the indent of the output json.
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:param prefix: an optional string prefix added at the beginning of
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the formatted string
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:param json_indent: indent parameter for json.dumps
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:param json_ensure_ascii: ensure_ascii parameter for json.dumps
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:param reserved_attrs: an optional list of fields that will be skipped when
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outputting json log record. Defaults to all log record attributes:
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http://docs.python.org/library/logging.html#logrecord-attributes
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:param timestamp: an optional string/boolean field to add a timestamp when
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outputting the json log record. If string is passed, timestamp will be added
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to log record using string as key. If True boolean is passed, timestamp key
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will be "timestamp". Defaults to False/off.
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"""
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self.json_default = self._str_to_fn(kwargs.pop("json_default", None))
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self.json_encoder = self._str_to_fn(kwargs.pop("json_encoder", None))
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self.json_serializer = self._str_to_fn(kwargs.pop("json_serializer", json.dumps))
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self.json_indent = kwargs.pop("json_indent", None)
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self.json_ensure_ascii = kwargs.pop("json_ensure_ascii", True)
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self.prefix = kwargs.pop("prefix", "")
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reserved_attrs = kwargs.pop("reserved_attrs", RESERVED_ATTRS)
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self.reserved_attrs = dict(zip(reserved_attrs, reserved_attrs))
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self.timestamp = kwargs.pop("timestamp", True)
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# super(JsonFormatter, self).__init__(*args, **kwargs)
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logging.Formatter.__init__(self, *args, **kwargs)
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if not self.json_encoder and not self.json_default:
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self.json_encoder = JsonEncoder
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self._required_fields = self.parse()
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self._skip_fields = dict(zip(self._required_fields,
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self._required_fields))
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self._skip_fields.update(self.reserved_attrs)
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def _str_to_fn(self, fn_as_str):
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"""
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If the argument is not a string, return whatever was passed in.
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Parses a string such as package.module.function, imports the module
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and returns the function.
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:param fn_as_str: The string to parse. If not a string, return it.
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"""
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if not isinstance(fn_as_str, str):
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return fn_as_str
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path, _, function = fn_as_str.rpartition('.')
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module = importlib.import_module(path)
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return getattr(module, function)
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def parse(self):
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"""
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Parses format string looking for substitutions
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This method is responsible for returning a list of fields (as strings)
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to include in all log messages.
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"""
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standard_formatters = re.compile(r'\((.+?)\)', re.IGNORECASE)
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return standard_formatters.findall(self._fmt)
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def add_fields(self, log_record, record, message_dict):
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"""
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Override this method to implement custom logic for adding fields.
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"""
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for field in self._required_fields:
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log_record[field] = record.__dict__.get(field)
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log_record.update(message_dict)
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merge_record_extra(record, log_record, reserved=self._skip_fields)
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if self.timestamp:
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key = self.timestamp if type(self.timestamp) == str else 'timestamp'
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log_record[key] = datetime.fromtimestamp(record.created, tz=utc)
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def process_log_record(self, log_record):
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"""
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Override this method to implement custom logic
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on the possibly ordered dictionary.
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"""
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return log_record
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def jsonify_log_record(self, log_record):
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"""Returns a json string of the log record."""
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return self.json_serializer(log_record,
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default=self.json_default,
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cls=self.json_encoder,
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indent=self.json_indent,
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ensure_ascii=self.json_ensure_ascii)
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def serialize_log_record(self, log_record):
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"""Returns the final representation of the log record."""
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return "%s%s" % (self.prefix, self.jsonify_log_record(log_record))
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def format(self, record):
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"""Formats a log record and serializes to json"""
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message_dict = {}
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# FIXME: logging.LogRecord.msg and logging.LogRecord.message in typeshed
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# are always type of str. We shouldn't need to override that.
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if isinstance(record.msg, dict):
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message_dict = record.msg
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record.message = None
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else:
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record.message = record.getMessage()
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# only format time if needed
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if "asctime" in self._required_fields:
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record.asctime = self.formatTime(record, self.datefmt)
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# Display formatted exception, but allow overriding it in the
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# user-supplied dict.
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if record.exc_info and not message_dict.get('exc_info'):
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message_dict['exc_info'] = self.formatException(record.exc_info)
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if not message_dict.get('exc_info') and record.exc_text:
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message_dict['exc_info'] = record.exc_text
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# Display formatted record of stack frames
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# default format is a string returned from :func:`traceback.print_stack`
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try:
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if record.stack_info and not message_dict.get('stack_info'):
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message_dict['stack_info'] = self.formatStack(record.stack_info)
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except AttributeError:
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# Python2.7 doesn't have stack_info.
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pass
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try:
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log_record = OrderedDict()
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except NameError:
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log_record = {}
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_inject_req_id(record, with_prefix=False)
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self.add_fields(log_record, record, message_dict)
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log_record = self.process_log_record(log_record)
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return self.serialize_log_record(log_record)
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