dispatch_request (/env/lib/python3.7/site-packages/flask/app.py:1935) [Flask on Google App Engine]

Question

I'm an English teacher in Japan. Because of COVID-19, my school has been shut down for a month and will be for another month. So I made a web app which my students can use to improve their English pronunciation at home.

The web app is very simple.

1. a web site with a text box

2. you input a sentence in the text box and click a button "submit"

3. you can download a mp3 file which is made by Google Cloud Text to Speech API

Here is my app's source code. https://github.com/k2kszk/speech-synthesizer I use Flask on Google App Engine standard environment Python3.7.

My students started using the web app, then I found error messages in Google Cloud Platform's console. Google Cloud Platform's console "Error Reporting" page. Here is the message.

File "/srv/main.py", line 20, in index: voiceid = next(voice for voice in request.form.getlist('voiceId[]') if accent in voice)
at dispatch_request (/env/lib/python3.7/site-packages/flask/app.py:1935)
at full_dispatch_request (/env/lib/python3.7/site-packages/flask/app.py:1949)
at reraise (/env/lib/python3.7/site-packages/flask/_compat.py:39)
at handle_user_exception (/env/lib/python3.7/site-packages/flask/app.py:1820)
at full_dispatch_request (/env/lib/python3.7/site-packages/flask/app.py:1951)
at wsgi_app (/env/lib/python3.7/site-packages/flask/app.py:2446)

I searched the Internet, but I couldn't find even what is the problem. How can I solve this error? Could you give me any advice or information?

Thank you in advance.

Sincerely, Kazu

++++++++++++++

Here is my main.py.

#./advance/main.py
from flask import Flask
from flask import render_template
from flask import request
from flask import send_file
import os
from google.cloud import texttospeech

app = Flask(__name__)

@app.route("/", methods=['POST', 'GET'])
def index():
    if request.method == "POST":
        if request.form['Radio'] == 'normal':
            ssml = '<speak><prosody rate="slow">' + request.form['text'] + '</prosody></speak>'
        else:
            ssml = '<speak>' + request.form['text'] + '</speak>'

        accent = request.form['accent']
        voiceid = next(voice for voice in request.form.getlist('voiceId[]') if accent in voice)
        os.environ["GOOGLE_APPLICATION_CREDENTIALS"]="credentials.json"

        client = texttospeech.TextToSpeechClient()
        input_text = texttospeech.types.SynthesisInput(ssml=ssml)
        voice = texttospeech.types.VoiceSelectionParams(
            language_code=accent,
            name=voiceid)

        audio_config = texttospeech.types.AudioConfig(
            audio_encoding=texttospeech.enums.AudioEncoding.MP3)

        response = client.synthesize_speech(input_text, voice, audio_config)

        # The response's audio_content is binary.
        with open('/tmp/output.mp3', 'wb') as out:
            out.write(response.audio_content)

        return send_file("/tmp/output.mp3",as_attachment=True)
    else:
        return render_template("index.html")

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

Answer 1

In this case the issue is on the voiceid line.

voiceid = next(voice for voice in request.form.getlist('voiceId[]') if accent in voice)

Which is raising StopIteration because its selection criteria is not satisfied. You can change it to

voiceid = voiceid = next((voice for voice in request.form.getlist('voiceId[]') if accent in voice), None) 

Then, voiceid will be set to None (or some other value you provide) in that situation.