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How to run server in development mode with flask?

I am learning to use flask and I want to run the server for an application in development mode, for this I do the following:
app = Flask(__name__)
if __name__=="__main__":
os.environ["FLASK_ENV"] = "development"
app.run(debug=True)
When I run I get the following in the terminal:
enter image description here
Environment:development does not appear to me as I understand it should appear. In fact, before doing this I don't get Environment:production either, I don't know what's going on. As a consequence, every time I want to see the changes that I am making in the code, I have to stop the server and run it again since the changes are not seen when refreshing the page.

If you're goal is for the application to restart each time code changes are saved, it shouldn't require any more than the following:
app = Flask(__name__)
if __name__=="__main__":
app.run(debug=True)
If you want to see what all your app config variables are set to by default, you can add the following line above app.run
print(app.config)
If you wanted to change your environment to production, change the 'ENV' variable after you initialize app
app = Flask(__name__)
app.config['ENV'] = 'production'
if __name__=="__main__":
app.run(debug=True)

Flaskserver running but not routing?

Hey I ran the flask basic code as follows -
from flask import Flask
app = Flask(__name__)
#app.route('/')
def hello_world():
return 'Hello, World!'
Then I ran the server as stated in docs and it ran fine.
But now when i got 127.0.0.1:5000/ nothing happens. The browser keeps circling as if refreshing the page but doesn't route.
Its my first python/flask code so I am not sure what I am doing wrong.
EDIT- By docs I mean quickstart documentation of flask. I know its fine cz i get this -
Serving Flask app "hello"
* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Just added app.run() to the same code and executed which is working fine. Can you try it?
from flask import Flask
app = Flask(__name__)
#app.route('/')
def hello_world():
return 'Hello, World!'
app.run()

I'm assuming that you're using this Quickstart - A Minimal Application.
That said let's make some points clear:
When you said
I know its fine cz i get this - Serving Flask app "hello"
You do not use the extension .py, which can cause some problems if you have another file with the same name in this directory. So make sure your FLASK_APP variable is correct.
This should work for you, but if the problem persist enable the Debug Mode adding
FLASK_ENV=development to your environment variable and see which error appears for you.
Hoping this solve your problem.

Python script with flask server takes too long to exit on Windows

I'm new to Python.
As a part of a project I'm trying to deploy a Flask server locally, through the Windows command line.
My Python version is 3.6.0.
The code:
from flask import Flask
app = Flask(__name__)
#app.route('/') def index():
return '<h1>Hello World!</h1>'
if __name__ == "__main__":
app.run()
The problem:
It's about killing the script as it runs. Launching this script with python deploy.py and hitting CTRL+C shuts it off.
BUT - if I hit access that '/' route via the browser once or more, and a moment later try to kill the script in the same manner, then it would take about 10 seconds of nothing until it responds and is finally killed.
Why is this happening? How can I shut the server off immediately each time for continuous and quick development?
Thanks!!

Well if your goal is continuous and quick development, then you can change flask's configuration.
Best solution for your problem would be setting the DEBUG setting to True. If DEBUG is set to True, then flask will automatically reload the server on code changes.
There are a few ways to do this but the easiest one(because you said you are a beginner) is to pass the debug argument to app.run()
from flask import Flask
app = Flask(__name__)
#app.route('/')
def index():
return '<h1>Hello World!</h1>'
if __name__ == "__main__":
app.run(debug=True)

Flask - 404 not found

I am a newbie in the flask development this is my first program in the flask but it shows me this error:
The requested URL was not found on the server. If you entered the URL
manually please check your spelling and try again.
& this is my code
from flask import Flask
app = Flask(__name__)
#app.route('/index')
def index():
return 'Hello World'
if __name__ == '__main__':
app.run(debug=True)

I think you should just go to http://localhost:5000/index or http://127.0.0.1:5000/index but if you want to make that page your code should be like that
from flask import Flask
app = Flask(__name__)
#app.route('/')
def index():
return 'Hello World'
if __name__ == '__main__':
app.run(debug=True)
change #app.route('/index') to #app.route('/') also you should check this http://flask.pocoo.org/docs/0.12/quickstart/#routing

You have to specify the route for index page as
#app.route('/')
If you give any other name to the template, you need to have to specify the name to the route.
For eg, if the template name is "home", then you have to give it as:
#app.route('/home')

I came across this question while having an almost similar problem. But in my case, the app.py would be executed, for the first time, then if i try to reload my localhost, maybe numerous times after making changes on my app.py the above cited error would be generated.
To solve this, i got a solution from this link: https://stackoverflow.com/a/44950213
Basically the last execution of python would continue running even after i updated my files and my console indicated a restart. So lets say you have made 3 changes while saving each change, then in the background you will have 3 instances of python.exe running. Depending on your OS, you will need to end these processes and re-execute your app.py.
So even if you use http://127.0.0.1:5000/index yet there are still instances of previous python.exe running, it may not execute
Note: this doesnt have to be the case all the time.

if you make the correct changes and it still doesn't work, I found out the hard way that the answer is to just save your file, and then run the program again.

I had the same problem. I created the home page which ran just fine:
#app.route('/')
def hello_world():
return 'Hello, World!'
But then when I tried making another page the next day:
#app.route('/bye/')
def bye():
return 'Bye!'
It gave me a 404 error.
So this is what I did to solve it:
Go to terminal ---> set FLASK_APP=youPythonfilename.py ------> flask run
After doing this the problem was solved. To avoid reloading everytime you need to set your debugger to ON.
if __name__ == '__name__':
app.run(debug=True)
After you have turned debugger ON by the above code, all you need to do is save the file everytime you make changes (windows - ctrl+s).

flask 'hello world' not working

I copy pasted the flask's 'hello world' app from their website and am trying to run it. I get an error message in Chrome saying
Internal Server Error
The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
Here is the 'hello world' app straight from flasks website
from flask import Flask
app = Flask(__name__)
#app.route('/')
def hello_world():
return 'Hello World!'
if __name__ == '__main__':
app.debug = True
app.run()
What I have tried:
-temporarily disabling Avast!
-disabling windows firewall
-ensuring that the flask module is installed
This was working a couple days ago actually...

I don't know why but when I change
app.run()
to
app.run(port=4996)
it starts working. No idea why the default port is throwing an error. Oh well.

from flask import Flask
app = Flask(__name__)
#app.route('/')
def index():
return 'Hello World'
if __name__ == '__name__':
app.run()
app.run(port=5000)

For Windows machines you can use the command in cmd:
set FLASK_APP=python_file.py
flask run

Some other process is running on port 5000. It may be you still have an old Flask process running, with broken code. Or a different web server altogether is running on that port. Shut down that process, or run on a different port.
You can switch to using a different port with the port argument to app.run():
app.run(port=8080)
If you can't figure out what process is still bound to port 5000, use the Windows Resource Monitor or run netstat -a -b from a command line. See How can you find out which process is listening on a port on Windows?

I think you are trying to copy the route generated through your flask program in cmd by pressing ctrl+c which quits your running flask program . i was also doing the same.just try to type the route generated by your flask program on your browser . it will definitely resolve your problem.

Where your python file store is, use cmd and then go on your file store directory, then
set FLASK_APP=filename.py
After this your flask run cmd will work.

from flask import Flask
app = Flask(__name__) # creating app
#app.route('/', methods['GET']) #routing it to the home page
def home(): #function
return "hello world"
app.run(port=5000, debug=true) #function call by the app
Add port and use methods whatever your need is USE GET in your case and try to remove your cache and run the this code it will definitely work.