Logging in Flask Into File: Introduction and Practical Example

app.py

# -*- encoding: utf-8 -*-
"""
python -m pip install flask
Python Application
"""

import os
from flask import Flask
from datetime import datetime
from logging.config import dictConfig

LOGGING_CONFIG = {
    # Always 1. Schema versioning may be added in a future release of logging
    "version": 1,
    # "Name of formatter" : {Formatter Config Dict}
    "formatters": {
        # Formatter Name
        "standard": {
            # class is always "logging.Formatter"
            "class": "logging.Formatter",
            # Optional: logging output format
            "format": '[%(asctime)s] %(levelname)8s in %(module)20s::%(lineno)5s %(message)s',
            # Optional: asctime format
            "datefmt": "%d %b %y %H:%M:%S"
        }
    },
    # Handlers use the formatter names declared above
    "handlers": {
        # Name of handler
        "console": {
            # The class of logger. A mixture of logging.config.dictConfig() and
            # logger class-specific keyword arguments (kwargs) are passed in here.
            "class": "logging.StreamHandler",
            # This is the formatter name declared above
            "formatter": "standard",
            "level": "INFO",
            # The default is stderr
            "stream": "ext://sys.stdout"
        },
        # Same as the StreamHandler example above, but with different
        # handler-specific kwargs.
        "file": {
            "class": "logging.handlers.RotatingFileHandler",
            "formatter": "standard",
            "level": "INFO",
            "filename": "application-" + datetime.now().strftime("%d-%m-%Y") + ".log",
            "mode": "a+",
            "encoding": "utf-8",
            "maxBytes": 500000,
            "backupCount": 4
        },
    },
    # Loggers use the handler names declared above
    "loggers": {
        # if __name__ == "__main__"
        "__main__": {
            # Use a list even if one handler is used
            "handlers": ["console", "file"],
            "level": "INFO",
            "propagate": False
        }
    },
    # Just a standalone kwarg for the root logger
    "root": {
        "level": "INFO",
        "handlers": ["file"]
    }
}
dictConfig(LOGGING_CONFIG)

app = Flask(__name__)


@app.route('/')
def auth_home():
    app.logger.info('This is a INFO_LOG')
    app.logger.warning('This is a WARN_LOG')
    app.logger.error('This is a ERROR_LOG')
    app.logger.critical('This is a CRITICAL_LOG')
    return '<H1>Welcome to User Authorization Module</H1>'


if __name__ == '__main__':
    host = str(os.environ.get("HOST", '0.0.0.0'))
    port = int(os.environ.get("PORT", 4300))
    debug = bool(os.environ.get("DEBUG", True))
    app.run(host=host, port=port, debug=debug)