How to get rid of 500 Internal Server Error using Python and Flask?

Question

I am getting an Internal Server Error on my website. When you go to the results page it'll throw the 500 Internal Server Error. I am not really sure why. It says I am getting a "KeyError: 'test'".

Here is the code in Python:

 @app.route('/results/')
def results():
    votes = {}
    for f in poll_data['fields']:
        votes[f] = 0

    f  = open(file, 'r+')
    for line in f:
        voted = line.rstrip("\n")
        votes[voted] += 1
        

    return render_template('results.html', data=poll_data, votes=votes)

And here is the "KeyError:" I am getting:

Here is some more code:

file = 'data0.txt'

 
@app.route('/')
def home():
    return render_template('home.html', data = poll_data)

@app.route('/poll')
def poll():
    vote = request.args.get('field')

    out = open(file, 'a+')
    out.write( vote + '\n' )
    out.close() 

    return render_template('thankyou.html', data = poll_data)

@app.route('/results/')
def results():
    votes = collections.defaultdict(int)
    for f in poll_data['fields']:
        votes[f] = 0

    f  = open(file, 'r+')
    for line in f:
        vote = line.rstrip("\n")
        votes[vote] += 1
        

    return render_template('results.html', data=poll_data, votes=votes)

@app.route('/contact/')
def contact():
    return render_template('contact.html')

@app.route('/helpfullinks/')
def helpfullinks():
    return render_template('helpfullinks.html')
    



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

Answer 1

The problem according to your screenshot is that votes does not have a key as the value of voted . If you change votes to be - votes=Counter() or votes=defaultdict(int) (both imported from collections that's should solve it)

Answer 2

This is just a hunch without more information but I bet the problematic line is this

voted = line.rstrip("\n")
votes[voted] += 1

As written the votes dictionary is populated from a different dataset, poll_data, than the one used to accumulate votes, "file". If a key exists in "file" that does not exist in poll_data you would expect to see the error you've written.

Based on this snippet you might benefit from the defaultdict in the collections module.

Add

import collections

Replace

votes = {}
for f in poll_data['fields']:
    votes[f] = 0

With

votes = collections.defaultdict(int)

The default dictionary will allow you retrieve values where no key exists which is what your code does with the += operator. In the case the default dictionary defaults the key value to the int function output which is zero.