Category: Python Answers

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Python Answers

How to fix Python Flask Value error view function did not return a response?

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Sometimes, we want to fix Python Flask Value error view function did not return a response.

In this article, we’ll look at how to fix Python Flask Value error view function did not return a response.

How to fix Python Flask Value error view function did not return a response?

To fix Python Flask Value error view function did not return a response, we should return a response in our view.

For instance, we write

@app.route('/')
def my_form():
    return render_template("my-form.html")

to call render_template with the template file name to return the template with the given file name as the response.

Conclusion

To fix Python Flask Value error view function did not return a response, we should return a response in our view.

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How to include a HTML file in a Jinja2 template with Python Flask?

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Sometimes, we want to include a HTML file in a Jinja2 template with Python Flask.

In this article, we’ll look at how to include a HTML file in a Jinja2 template with Python Flask.

How to include a HTML file in a Jinja2 template with Python Flask?

To include a HTML file in a Jinja2 template with Python Flask, we can use the include directive.

For instance, we write

{% extends 'template.html' %}
{% block content %}
    {% if task == 'content1' %}
        {% include 'content1.html' %}
    {% endif %}
    {% if task == 'content2' %}
        {% include 'content2.html' %}
    {% endif %}
{% endblock %}

to render content1.html and content2.html‘s contents with

{% include 'content1.html' %}

and

{% include 'content2.html' %}

Conclusion

To include a HTML file in a Jinja2 template with Python Flask, we can use the include directive.

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How to download a csv file on clicking a button with Python Flask?

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Sometimes, we want to download a csv file on clicking a button with Python Flask.

in this article, we’ll look at how to download a csv file on clicking a button with Python Flask.

How to download a csv file on clicking a button with Python Flask?

To download a csv file on clicking a button with Python Flask, we can add a link that goes to the view that returns the csv as the response.

For instance, we write

from flask import Flask, Response
app = Flask(__name__)

@app.route("/")
def hello():
    return '''
        <html>
          <body>
            <a href="/get_csv">Click me.</a>
          </body>
        </html>
      '''

@app.route("/get_csv")
def get_csv():
    csv = '1,2,3\n4,5,6\n'
    return Response(
        csv,
        mimetype="text/csv",
        headers={"Content-disposition":
                 "attachment; filename=myplot.csv"})


app.run(debug=True)

to create the hello route that renders the HTML with the link.

Then add the get_csv view that returns the csv as the response by creating a Response object with mimetype set to 'text/csv' and the csv as the content.

Now when we click on the link, the csv should be downloaded as myplot.csv.

Conclusion

To download a csv file on clicking a button with Python Flask, we can add a link that goes to the view that returns the csv as the response.

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How to make a Python asyncio call from a Flask route?

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Sometimes, we want to make a Python asyncio call from a Flask route.

In this article, we’ll look at how to make a Python asyncio call from a Flask route.

How to make a Python asyncio call from a Flask route?

To make a Python asyncio call from a Flask route, we can call run_until_complete.

For instance, we write

import asyncio
from flask import Flask

async def foo(a):
    print(a)

loop = asyncio.get_event_loop()
app = Flask(__name__)

@app.route("/")
def notify():
    loop.run_until_complete(foo("abc"))
    return "OK"

if __name__ == "__main__":
    app.run(debug=False, use_reloader=False)

to create the event loop with get_event_loop.

Then we call loop.run_until_complete with the async function to run in the notify view.

Conclusion

To make a Python asyncio call from a Flask route, we can call run_until_complete.

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How to install Python Flask on Windows?

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Sometimes, we want to install Python Flask on Windows.

In this article, we’ll look at how to install Python Flask on Windows.

How to install Python Flask on Windows?

To install Python Flask on Windows, we install the flask package with pip.

To install it, we run

pip install Flask

Then we create the app.py file and write

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

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

to create a simple app.

And then we run it by going to the Flask app project directory and run

python app.py

Conclusion

To install Python Flask on Windows, we install the flask package with pip.