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Python Flask app route is not working well

I tried to find a solution for my problem in other questions but I couldn't.
I downloaded the python flask and made my first flask app and it ran fine.
Here is the code:
from flask import Flask
app = Flask(__name__)
#app.route("/")
def index():
return "Hello, world!"
When I ran my second file where I had added an app.route ("/ david") and followed the same procedure again, refreshed it and nothing changed.
That is to say, I was going to / david and I get an URL error
Here is my second file
from flask import Flask
app = Flask(__name__)
#app.route("/")
def index():
return "Hello, world!"
#app.route("/david")
def david():
return "Hello, David!"
I tried the same with other files which have some added routes and the result is the same as the first file
Thanks for your answers, I hope to solve my problem.

You did not run the app. What you did is just create a structure for flask, but did not start the server.
Just add:
app.run()
To the bottom of the file and it will work. It will with start the flask server at http://localhost:5000.
By default, flask runs on port 5000.
It can be changed by:
app.run(host="0.0.0.0", port=xxxx)
0.0.0.0 means it accepts request from anywhere on the port specified.
Make sure you have all the permissions and nothing else is running if you want it to run on port 80.
Hope this helps. Good luck.

I had the same issue. Try first by restarting your IDE; this worked for me. If that doesn't work, try clearing your ports for Windows:
Open Task manager
Click on the “Processe” tab
Enable the "PID" column: View -> Select Columns -> Check the box for PID
Find the PID (in your case, 5000 - flask default port) and click “END PROCESS"

I can't go to the other paths i am using flask

I am studying this course on flask. This is the basic flask code. When I am on the first route I am fine but when I try to put slash and got for another page it doesn't work.
I get this message:
"The requested URL was not found on the server. If you entered the URL manually please check your spelling and try again."
I did run FLASK_APP=app.py flask run
after saving.
from Flask import flask
app= Flask(__name__)
#app.route('/')
def index():
return "index"
#app.route('/me')
def me():
return "me"
if __name__== "__main__":
app.run(debug=True)
In class it works well. When i do it it does not
127.0.0.1 - - [08/Jul/2019 02:43:55] "GET /me/ HTTP/1.1" 404 -
I'm guessing 404 at the end is problem
After the reply
from Flask import flask
app= Flask(__name__)
strict_slashes=False
#app.route('/')
def index():
return "index"
#app.route('/me/')
def me():
return "me"
if __name__== "__main__":
app.run(debug=True)

You have declared your "/me" route explicitly without trailing slash. However, when calling the URL, you are calling it with slash in the end "/me/". Werkzeug (Flask development application server) by default has the rule of "strict_slashes=True", which requires you to follow exact route declaration when calling your URLs. In other words, if in your code, you declared "#app.route('/me'), your should call "127.0.0.1/me", not "127.0.0.1/me/".
Removing the slash in the end (e.g. http://localhost/me) will fix your issue. You can also change the Werkzeug setting and set strict_slashes=False if you want to remove the default rule.

I would say make a app.errorhandler(404) and then define what to do after you get an error to check if it is a 404 error, and other errors. I would also say use html and make links which you can use to go into different pages, it is easier than typing manually. here is my code:
python:
from flask import Flask, render_template
app = Flask(__name__)
app.route('/')
def home():
return render_template('home.html')
app.route('/me')
def me():
return 'me'
app.errorhandler(404)
def error(arg):
return 'wrong url'
if __name__ == "__main__":
app.run(host="0.0.0.0", port=8080)
html:
<!-- you can use css to make the link look better or <style> </style>-->

Angular router not engaging with Flask server using ng build

When using Angular 5 with Flask and ng build --aot --watch, I am having major issues getting Angular's routing and refreshing the page to work.
I have come across many attempts to fix this, but none of them when applied to my project work (and the example projects provided when I try it there also do not seem to work).
What happens (depending on the thing I try) are these:
It can't find the path at all and I get a Jinja2 error
It can't find the document for localhost:5015/ (the port I'm using) and I get a 404 and a white screen
It loads index.html, but upon refresh it gets a 404 (implying that the browser is attempting to fetch the page from the server, not using the Angular routing system)
I get the same issue as this one: Syntax Error in Angular App: Unexpected token <
I am under the impression this is a normal issue with all SPAs and that the solution is to always redirect the server to index.html. We have done this (AFAIK), and attempted multiple ways to do this:
Our structure is roughly the following:
- ProjectDir
- reverseProxy_Calls
- scripts
- swagger_yaml_definitions
- templates
- e2e
- dist
- src
- app
And our server.py contains this (among other stuff)
Swagger(app)
app.template_folder = "./templates/dist/"
app.static_folder = "./templates/dist/"
app.static_path = "./templates/dist/"
app.static_url_path = "./templates/dist/"
app.instance_path = "./templates/dist/"
config = settings.config()
config.read("settings.cfg")
#app.route('/', defaults={'path': ''}, methods=['GET', 'POST'])
#app.route('/<path:path>', methods=['GET', 'POST'])
def get_resource(path): # pragma: no cover
# If we are devmode, proxy through flask.
if config.getKey("devmode") == True:
url = "http://localhost:%s/%s" % (config.getKey('ng_port'), path)
j = requests.get(url, stream=True, params=request.args)
return make_response(j.text)
# return the results
# return render_template('dist/index.html')
# return app.send_static_file("index.html")
return send_from_directory('dist/', path)
if __name__ == '__main__':
app.run(debug=True, port=int(config.getKey("port"))) # , host='0.0.0.0')
^ A variety of ways here show various attempts to handle this.
I have also looked at and tried projects that use variations of the following:
Flask Cli
Flask-Script
Flask-Bootstrap
None of them have solved this problem when I have tried them.
I have been told that using the hashRoute location strategy in Angular rather than the History PushState strategy will also work, however when I attempted to do that it had the same behavior of losing the page upon refresh (additionally we wish to use server side rendering in the future, and hashRoute location strategy prevents this possibility, among many other downsides).
Possibly related is that Flask seems to reload or re-render the page when it does find the index.html and routes initially, wiping anything printed to the browser dev console. I have seen this in some of the flask examples, but not all, and I'm uncertain what causes this.
When running via ng serve --aot --prod, things work exactly correctly and as expected. It's only when serving via Flask that things break down.
Apologies for the long question and thank you for your time in advance.

I am under the impression this is a normal issue with all SPAs and
that the solution is to always redirect the server to index.html. We
have done this (AFAIK), and attempted multiple ways to do this
You also need to redirect all HTTP errors to index.html.

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).

Python/Flask Rest API not passing preflight w/CORS

I am trying to get the simplest rest api up that I can in python and I am having trouble. I'm not sure what I am doing wrong, but I think it has something to do with CORS. This is frustrating, as I have used the flask_cors package in order to fix this and it does not appear to work.
In my main.py file i have the following
from flask import Flask
from flask_cors import CORS, cross_origin
app = Flask(__name__)
CORS(app)
import routes.login
if __name__ == '__main__':
app.run(debug=True)
For my project I have this as my folder structure:
main.py
__init__.py
routes
__init__.py
login.py
And i have the following code in login.py
from flask import Flask
from flask_cors import CORS, cross_origin
from main import app
CORS(app)
#app.route('/login', methods=['POST', 'GET'])
#cross_origin()
def login(name, password):
if request.method == 'POST':
print('inside login POST')
if request.method == 'GET':
print('inside login GET')
I'm currently getting this error:
xhr.js:178 OPTIONS http://localhost:5000/login 404 (NOT FOUND)
dispatchXhrRequest # xhr.js:178
xhrAdapter # xhr.js:12
dispatchRequest # dispatchRequest.js:52
:3000/pictureswapper:1 XMLHttpRequest cannot load http://localhost:5000/login.
Response for preflight has invalid HTTP status code 404
There is some sort of CORS error, but I really don't know what's going wrong. Any ideas?
EDIT: The only place in the documentation that has anything to say about preflight is here (https://flask-cors.readthedocs.io/en/v1.3.1/index.html?highlight=preflight). If I add
#cross_origin(headers=['Content-Type']) # Send Access-Control-Allow-Headers
It doesn't break the application, but neither does it fix the error.

Revisiting this after a few months.
One of the nasty gotchas in python/flask appears to be that the compiled code will get cached, so if you change something at the entrypoint of the app (ie main.py), and don't delete the binaries that flask export creates then every time you run flask export and recompile it may be using old code!
Make sure to delete (in atom they are the purple 1/0 files -if you have file icons enabled- labeled .pyc) these files if you are getting spooky output.

Add OPTIONS to the methods keyword of your route decorator, or remove that keyword altogether.