Control .py with Flask and Buttons

Question

What is necessary to get a button on a webpage work with flask? I just want to turn a LED on.

the html looks like:

<tr>
  <td><h3>Computer</h3></td>
  <td><p><input type="submit" name="btnled" value="ON"></p></td>
  <td><p><input type="submit" name="btnled" value="OFF"></p></td>
</tr>

How can i catch the pressed button in python to turn the led on? What do i need? WTForms?

Edit:

the .py looks like this:

from flask import request
@app.route("/switch_led", methods=['POST'])
def led_handler():
    if request.form['btnled'] == "ON":
        print("ON")
    elif request.form['btnled'] == "OFF":
        print("OFF")

Miguel Grinberg · Accepted Answer · 2014-03-31 14:36:08Z

4

No need for a forms framework for something so simple.

You need to wrap the buttons in a form element, with an action pointing at your handler URL:

<form action="/switch_led" method="POST">
  <p><input type="submit" name="btnled" value="ON"></p>
  <p><input type="submit" name="btnled" value="OFF"></p>
</form>

And in the handler class:

from flask import request

@app.route('/switch_led', methods=['POST'])
def led_handler():
    if request.form['btnled'] == "ON":
        # do ON action
    elif request.form['btnled'] == "OFF":
        # do OFF action

edited Mar 31, 2014 at 14:36

Miguel Grinberg

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answered Mar 31, 2014 at 13:10

Daniel Roseman

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6 Comments

lengi Over a year ago

I only get this when i run the .py file and click on the button:

192.168.178.65 - - [01/Apr/2014 14:18:58] "GET /?btnled=ON HTTP/1.1" 200 - 192.168.178.65 - - [01/Apr/2014 14:18:58] "GET /home HTTP/1.1" 200 -

Daniel Roseman Over a year ago

Then your template is wrong, as that is clearly a GET request and the template I show above has a POST, and it is requesting / rather than /switch_led.

lengi Over a year ago

you're right! i forgot to delete a old form. I get POST now but there is a new problem. When i click on the button, i get the error page with the error ValueError: View function did not return a response. Is this because i only have a print("ON") in my if function?

Daniel Roseman Over a year ago

Yes, your view always needs to return a response, even if it's just return 'ON'.

lengi Over a year ago

Is there no way to avoid this? When i insert the return 'ON', it opens a new blank page just saying "ON" but i don't want to change the site because i can't see all of my buttons anymore. I tried to retrun the html with the buttons and it works, but i want to load the html a second time. Is there a way to return anything that really nothing happens on my webpage?

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