Unexplainable Flask 404 errors

Question

I have a website that uses Flask. It used to work well, but since recently, every request returns a 404, and it seems it can't find the right endpoints. However:

• Locally, the site still works, only on my VPS it shows this strange behaviour.
• url_for works and app.view_functions contains all the routes as well.
• And yet, I keep getting 404s on the VPS, even for / and anything under /static/.

Here's part of the code, it's a bit much to show all of it and it's not all relevant:

#snip

from flask import Flask, render_template, abort, request, redirect, url_for, session
from flask.ext.babelex import Babel
from flask.ext import babelex

#snip

app = Flask(__name__)
app.secret_key = #snip

#snip

#just one of the routes
@app.route('/')
def about():
    return render_template('about.html')

#snip

@app.errorhandler(404)
def page_not_found(e):
    #snip
    return render_template('404.html'), 404

#snip

if __name__ == '__main__':
    app.run(debug=True)
else:
    app.config.update(
        SERVER_NAME='snip.snip.com:80',
        APPLICATION_ROOT='/',
    )

Answer 1

I had the same issue. I had it because I changed the parameters SERVER_NAMEof the config to a name which is not the name of the server.

You can solve this bug by removing SERVER_NAME from the config if you have it.

Answer 2

Had the same issue because the following lines

if __name__ == '__main__':
    app.run(host='127.0.0.1', threaded=True)

were declared before the function and decorator.

Moving these lines in the very bottom of file helped me.

Answer 3

I know this is old, but I just ran into this same problem. Yours could be any number of issues but mine was that I had commented out the from app import views line in my __init__.py file. It gave me the same symptom: every endpoint that required @app.route and a view was responding with 404's. Static routes (.js and .css) were fine (that was my clue).

Answer 4

Extremely old by this point, but mine was related to bug in importing. I'm using blueprints and I had:

from app.auth import bp

instead of

from app.main import bp

I was importing the wrong bp/ routes

Answer 5

I received this error from defining my flask_restful route inside the create_app method. I still don't quite understand why it didn't work but once I changed the scope / moved it outside as shown below it worked.

from flask import Flask
from flask_restful import Resource
from extensions import db, api
from users.resources import User

def create_app():
    app = Flask(__name__)
    app.config.from_object('settings')
    db.init_app(app)
    api.init_app(app)

    return app

api.add_resource(User, '/users') 

Answer 6

Also check carefully the routes. If some does not end with a slash but you are calling it with a trailing slash, flask will return a 404.

I had this error following a url from an email client that (I don't know why) append a trailing slash to the urls.

See documentation.

Answer 7

I had this problem and in my case it was about my templates. I had an index page like this:

<div>
    <a href="index.html">Home</a> |
    <a href="login.html">Login</a> |
    <a href="register.html">Register</a>
    <hr>
</div>

I should have used url_for('index') instead of index.html.

<div>
    <a href="{{ url_for('index') }}">Home</a> |
    <a href="{{ url_for('login') }}">Login</a> |
    <a href="{{ url_for('register') }}">Register</a>
    <hr>
</div>

Answer 8

For me, I was getting 404s on every request due to missing favicon.ico and manifest.json. The solution was to provide the missing favicon.ico, and remove the link rel refence to manifest.json.

I found this out by printing the path that was causing problems on every request in my @app.errorhandler(Exception):

from flask import request

@app.errorhandler(Exception)
def handle_exception(err):
  path = request.path # this var was shown to be 'favicon.ico' or 'manifest.json'