Flask doesn't print to console

Question

I\'m new to flask, and I\'m trying to add print info to debug server side code. When launch my flask app with debug=True, i can\'t get any info print to console

I tr

Answer 1

By default the level for logging is warning. So you won't see a logging message of level DEBUG. To fix this just enable debug logging with the basicConfig() function of the logging module:

import logging
logging.basicConfig(level=logging.DEBUG)

Answer 2

Try this and see if it helps:

For python2:

from __future__ import print_function
import sys

print('This is error output', file=sys.stderr)
print('This is standard output', file=sys.stdout)

For python3 you don't need to import from future print_function:

import sys

print('This is error output', file=sys.stderr)
print('This is standard output', file=sys.stdout)

See if it helps to print to console.

Answer 3

You can force to flush stdout directly from print:

print('enter getJSONReuslt', flush=True)

This way you don't have to print to sys.stderr (which flushes by default).

The reason for your problem is line buffering. Line buffering makes I/O more efficient with the drawback of not immediately showing prints under some conditions.

Answer 4

you can use the app instance in development mode besause the logging level is set to DEBUG app.logger.info('This is info output') in production mode you need to use a more sever level or you can set the logging level to DEBUG

from flask import Flask
import logging

app = Flask(__name__)

logging.basicConfig(level=logging.DEBUG)

@app.route('/')
def hello_world():
    app.logger.info('Processing default request')
    return 'Hello World!'

if __name__ == '__main__':
    app.run()

this article talk about logging into flask https://www.scalyr.com/blog/getting-started-quickly-with-flask-logging/

Answer 5

Had the same printing problem. Using sys.stdout.flush() after the print solved the issue.