How does Python use logging to add logid to Flask

Directory logid save and transfer
Print log automatically brings logid

In order to locate the problem, the common practice is to add logid to the log, which is used to associate the context of 1 request. This involves two problems: 1. How to save and pass the "global" variable logid. 2. How to automatically bring logid when printing logs (after all, you can't manually pass in every place where logs are typed)

logid save and transfer

Traditionally, logid is stored in threading. local, and every thread has a value of one kind. It is generated at before_app_request, and logid is put in.

import threading
 
from blueprint.hooks import hooks
 
thread_local = threading.local()
app = Flask()
app.thread_local = thread_local

import uuid
 
from flask import Blueprint
from flask import current_app as app
 
hooks = Blueprint('hooks', __name__)
 
@hooks.before_app_request
def before_request():
    """
     Hook before processing request 
    :return:
    """
    #  Generate logid
    app.thread_local.logid = uuid.uuid1().time

uuid. uuid 1 (). time 1-like concurrency is enough, without repetition and with increasing trends (see logid to tell when the request is coming or going).

Automatic print log with logid

This is the Python log library features, you can use Filter to achieve this requirement.

import logging
 
# https://docs.python.org/3/library/logging.html#logrecord-attributes
log_format = "%(asctime)s %(levelname)s [%(threadName)s-%(thread)d] %(logid)s %(filename)s:%(lineno)d %(message)s"
file_handler = logging.FileHandler(file_name)
logger = logging.getLogger()
logid_filter = ContextFilter()
file_handler.addFilter(logid_filter)
file_handler.setFormatter(logging.Formatter(log_format))
logger.addHandler(file_handler)
 
class ContextFilter(logging.Filter):
    """
    logging Filter
    """
 
    def filter(self, record):
        """
        threading local  Get logid
        :param record:
        :return:
        """
        log_id = thread_local.logid if hasattr(thread_local, 'logid') else '-'
        record.logid = log_id
 
        return True

In log_format we use many of the system's own placeholders, but% (logid) s does not have them by default. Each log will pass Filter before printing out. By using this feature, we can assign record. logid, and logid will be available when it is finally printed out.

Although it was finally realized, it was somewhat complicated because it was a general scheme. In fact, the official tutorial introduces a simpler way: injecting-request-information. It seems that there is nothing wrong with reading the official documents.

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