error_app.py

import os
import logging

from flask import Flask
app = Flask(__name__)

log_formatter = logging.Formatter(
    '[%(levelname)s] %(asctime)s %(message)s'
)
app.logger = logging.getLogger()
app.logger.setLevel(logging.INFO)

# Log to a file
filename = 'flask.log'
cd = os.path.dirname(os.path.realpath(__file__))  # current directory
log_path = os.path.join(cd, filename)  # build platform independent path
fileHandler = logging.FileHandler(log_path)
fileHandler.setFormatter(log_formatter)
app.logger.addHandler(fileHandler)

# Log to standard error
stderrHandler = logging.StreamHandler()
stderrHandler.setFormatter(log_formatter)
app.logger.addHandler(stderrHandler)

@app.route('/')
def home():
    app.logger.info('Log Hello World!')
    return """
        Hello World!
    """