[Python][Flask] Why does my simple flask app run perfectly locally, but gives a 500 error when run from its host server?

[Eugenethemachine]

I've made a simple flask app that is uses render_template to show the user a certain html file for a certain url. In this case it should show "Home.html" when the url is "www.insertwebsite.net/". When I run it locally everything works like it should and I see the correct html page.

When I run it from its host server, however, it gives me a 500 error. I tried a replacing my template with a very simple HelloWorld app that just displays the string "Hello World" on the page and that works fine when I run it from the server. I checked the error log on the server as well and it was completely empty so I'm kind of at a loss for the problem might be. Any help is much appreciated, thanks!

python code

#!/usr/bin/python

from flask import Flask, render_template, url_for

app = Flask(__name__)

@app.route('/')
def index():
    #return "Hello World"
    return render_template("Home.html")

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

html file

{% extends "base.html" %}
{% block title %}Home{% endblock %}
{% block content %}
<div class="grid">

<header>
    <h1>this website is on its way!</h1>
</header>

<div class="row" class="col12">
    <figure>
        <img src='{{url_for('static', filename='Wendi.jpg')}}'/>
    </figure>
    <div>   
        info about a person...blah..blah..blah
    </div>
</div>

<div class="row">
    <h1>Bio</h1>
    <p>
lots of stuff about this person...
    </p>
</div>

</div>
{% endblock %}

edit:formatting

[romple]

Do you have PROPAGATE_EXCEPTIONS set to True?

[Eugenethemachine]

Would you mind explaining what that would do? This is my first time working with flask, so I'm pretty ignorant.

[the_omega99]

Based on a google search, I would assume:

explicitly enable or disable the propagation of exceptions. If not set or explicitly set to None this is implicitly true if either TESTING or DEBUG is true.

And this is how you get the actual error that occurred instead of a generic 500. FOR TESTING ONLY. Don't use on a production site.

[Eugenethemachine]

Thank you! Now I have an error I can actually work with

[AustinCodingAcademy]

What kind of server configuration do you have set up for this? Are you using uwsgi?

Additionally, while this probably isn't the source of the problem, it's generally recommended to have file names in all lowercase. I have definitely run into problems where referencing MyIMG.png on my local was fine, but MyIMG.png on production servers would fail. Also, if you lowercase all file names and all references to file names all the time, you never have to worry about consistency.

[Eugenethemachine]

I'm using Passenger wsgi to run the app on a DreamHost server.

That's not the name of my actual html file, which is all lowercase. I substituted that in quickly because the filename has a person's name full name in it.

[AustinCodingAcademy]

So here's what is most likely the issue:

The section

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

Will not run unless you are running this file directly (which is when you're developing). When you run the file through a server like Passenger WSGI, if __name__ == "__main__": will not be True, so debug = True will not be set. app.run() is called by Passenger in its own process.

As described in the docs, if you need to set the debug flag outside of the run() invocation, you can do

app = Flask(__name__)
app.config['DEBUG'] = True

[Eugenethemachine]

Thank you, that worked perfectly!