CODEWITHSUNDEEP
pythonflask
Robert Filter
Robert Filter

Reputation: 1721

How to print from Flask @app.route to python console

I would like to simply print a "hello world" to the python console after /button is called by the user.

This is my naive approach:

@app.route('/button/')
def button_clicked():
    print 'Hello world!'
    return redirect('/')

Background: I would like to execute other python commands from flask (not shell). "print" should be the easiest case. I believe I have not understood a basic twist here.

Upvotes: 128

Views: 217029

Answers (4)

Gabe
Gabe

Reputation: 1812

An easy way to do this is by printing to stderr. You can do that like this:

from __future__ import print_function # In python 2.7
import sys

@app.route('/button/')
def button_clicked():
    print('Hello world!', file=sys.stderr)
    return redirect('/')

Flask will display things printed to stderr in the console. For other ways of printing to stderr, see this stackoverflow post

Upvotes: 163

Saurabh
Saurabh

Reputation: 6920

I tried running @Viraj Wadate's code, but couldn't get the output from app.logger.info on the console.

To get INFO, WARNING, and ERROR messages in the console, the dictConfig object can be used to create logging configuration for all logs (source):

from logging.config import dictConfig
from flask import Flask


dictConfig({
    'version': 1,
    'formatters': {'default': {
        'format': '[%(asctime)s] %(levelname)s in %(module)s: %(message)s',
    }},
    'handlers': {'wsgi': {
        'class': 'logging.StreamHandler',
        'stream': 'ext://flask.logging.wsgi_errors_stream',
        'formatter': 'default'
    }},
    'root': {
        'level': 'INFO',
        'handlers': ['wsgi']
    }
})


app = Flask(__name__)

@app.route('/')
def index():
    return "Hello from Flask's test environment"

@app.route('/print')
def printMsg():
    app.logger.warning('testing warning log')
    app.logger.error('testing error log')
    app.logger.info('testing info log')
    return "Check your console"

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

Upvotes: 5

Chris
Chris

Reputation: 5484

I think the core issue with Flask is that stdout gets buffered. I was able to print with print('Hi', flush=True). You can also disable buffering by setting the PYTHONUNBUFFERED environment variable (to any non-empty string).

Upvotes: 27

Viraj Wadate
Viraj Wadate

Reputation: 6123

We can also use logging to print data on the console.

Example:

import logging
from flask import Flask

app = Flask(__name__)

@app.route('/print')
def printMsg():
    app.logger.warning('testing warning log')
    app.logger.error('testing error log')
    app.logger.info('testing info log')
    return "Check your console"

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

Upvotes: 41

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