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Edit File: _flatten.py
# -*- test-case-name: twisted.logger.test.test_flatten -*- # Copyright (c) Twisted Matrix Laboratories. # See LICENSE for details. """ Code related to "flattening" events; that is, extracting a description of all relevant fields from the format string and persisting them for later examination. """ from collections import defaultdict from string import Formatter from typing import Any, Dict, Optional from ._interfaces import LogEvent aFormatter = Formatter() class KeyFlattener: """ A L{KeyFlattener} computes keys for the things within curly braces in PEP-3101-style format strings as parsed by L{string.Formatter.parse}. """ def __init__(self) -> None: """ Initialize a L{KeyFlattener}. """ self.keys: Dict[str, int] = defaultdict(lambda: 0) def flatKey( self, fieldName: str, formatSpec: Optional[str], conversion: Optional[str] ) -> str: """ Compute a string key for a given field/format/conversion. @param fieldName: A format field name. @param formatSpec: A format spec. @param conversion: A format field conversion type. @return: A key specific to the given field, format and conversion, as well as the occurrence of that combination within this L{KeyFlattener}'s lifetime. """ if formatSpec is None: formatSpec = "" if conversion is None: conversion = "" result = "{fieldName}!{conversion}:{formatSpec}".format( fieldName=fieldName, formatSpec=formatSpec, conversion=conversion, ) self.keys[result] += 1 n = self.keys[result] if n != 1: result += "/" + str(self.keys[result]) return result def flattenEvent(event: LogEvent) -> None: """ Flatten the given event by pre-associating format fields with specific objects and callable results in a L{dict} put into the C{"log_flattened"} key in the event. @param event: A logging event. """ if event.get("log_format", None) is None: return if "log_flattened" in event: fields = event["log_flattened"] else: fields = {} keyFlattener = KeyFlattener() for (literalText, fieldName, formatSpec, conversion) in aFormatter.parse( event["log_format"] ): if fieldName is None: continue if conversion != "r": conversion = "s" flattenedKey = keyFlattener.flatKey(fieldName, formatSpec, conversion) structuredKey = keyFlattener.flatKey(fieldName, formatSpec, "") if flattenedKey in fields: # We've already seen and handled this key continue if fieldName.endswith("()"): fieldName = fieldName[:-2] callit = True else: callit = False field = aFormatter.get_field(fieldName, (), event) fieldValue = field[0] if conversion == "r": conversionFunction = repr else: # Above: if conversion is not "r", it's "s" conversionFunction = str if callit: fieldValue = fieldValue() flattenedValue = conversionFunction(fieldValue) fields[flattenedKey] = flattenedValue fields[structuredKey] = fieldValue if fields: event["log_flattened"] = fields def extractField(field: str, event: LogEvent) -> Any: """ Extract a given format field from the given event. @param field: A string describing a format field or log key. This is the text that would normally fall between a pair of curly braces in a format string: for example, C{"key[2].attribute"}. If a conversion is specified (the thing after the C{"!"} character in a format field) then the result will always be str. @param event: A log event. @return: A value extracted from the field. @raise KeyError: if the field is not found in the given event. """ keyFlattener = KeyFlattener() [[literalText, fieldName, formatSpec, conversion]] = aFormatter.parse( "{" + field + "}" ) assert fieldName is not None key = keyFlattener.flatKey(fieldName, formatSpec, conversion) if "log_flattened" not in event: flattenEvent(event) return event["log_flattened"][key] def flatFormat(event: LogEvent) -> str: """ Format an event which has been flattened with L{flattenEvent}. @param event: A logging event. @return: A formatted string. """ fieldValues = event["log_flattened"] keyFlattener = KeyFlattener() s = [] for literalText, fieldName, formatSpec, conversion in aFormatter.parse( event["log_format"] ): s.append(literalText) if fieldName is not None: key = keyFlattener.flatKey(fieldName, formatSpec, conversion or "s") s.append(str(fieldValues[key])) return "".join(s)