Flask - Calling python function on button OnClick event

I am new to python and Flask. I have a Flask Web App with a button. When I click on the button I would like to execute a python method not a Javascript method. How can I do this?

I have seen examples with python where it redirects me to a new page using a form tag like this

<form action="/newPage" method="post">

but I don't want it to redirect me to a new page. I just want it to execute the python method. I am making this for a Raspberry Pi robot car. When I press the forward button, I want it to run the method to Turn wheels forward.

Button HTML Code (index.html)

<button name="forwardBtn" onclick="move_forward()">Forward</button>

simple app.py Code - move_forward() method located here

#### App.py code

from flask import Flask, render_template, Response, request, redirect, url_for
app = Flask(__name__)

@app.route("/")
def index():
    return render_template('index.html');
    
def move_forward():
    #Moving forward code
    print("Moving Forward...")

I have seen similar questions to mine on Stackoverflow, but they don't seem to answer my question or I am unable to understand the answer. If someone could please provide me a simple way to call a Python method on button click event, it would be greatly appreciated.

Other Questions that I have looked at:

--https://stackoverflow.com/questions/30899484/python-flask-calling-functions-using-buttons

--https://stackoverflow.com/questions/40583347/calling-a-python-function-with-a-button

--https://stackoverflow.com/questions/21566649/flask-button-run-python-without-refreshing-page

You can simply do this with help of AJAX... Here is a example which calls a python function which prints hello without redirecting or refreshing the page.

In app.py put below code segment.

#rendering the HTML page which has the button
@app.route('/json')
def json():
    return render_template('json.html')

#background process happening without any refreshing
@app.route('/background_process_test')
def background_process_test():
    print ("Hello")
    return ("nothing")

And your json.html page should look like below.

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script type=text/javascript>
		$(function() {
		  $('a#test').on('click', function(e) {
            e.preventDefault()
			$.getJSON('/background_process_test',
                function(data) {
			  //do nothing
			});
			return false;
		  });
		});
</script>


//button
<div class='container'>
	<h3>Test</h3>
		<form>
			<a href=# id=test><button class='btn btn-default'>Test</button></a>
		</form>

</div>

Here when you press the button Test simple in the console you can see "Hello" is displaying without any refreshing.

It sounds like you want to use this web application as a remote control for your robot, and a core issue is that you won't want a page reload every time you perform an action, in which case, the last link you posted answers your problem.

I think you may be misunderstanding a few things about Flask. For one, you can't nest multiple functions in a single route. You're not making a set of functions available for a particular route, you're defining the one specific thing the server will do when that route is called.

With that in mind, you would be able to solve your problem with a page reload by changing your app.py to look more like this:

from flask import Flask, render_template, Response, request, redirect, url_for
app = Flask(__name__)

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

@app.route("/forward/", methods=['POST'])
def move_forward():
    #Moving forward code
    forward_message = "Moving Forward..."
    return render_template('index.html', forward_message=forward_message);

Then in your html, use this:

<form action="/forward/" method="post">
    <button name="forwardBtn" type="submit">Forward</button>
</form>

...To execute your moving forward code. And include this:

{{ forward_message }} 

... where you want the moving forward message to appear on your template.

This will cause your page to reload, which is inevitable without using AJAX and Javascript.

Easiest solution

<button type="button" onclick="window.location.href='{{ url_for( 'move_forward') }}';">Forward</button>

index.html (index.html should be in templates folder)

<!doctype html>
<html>

<head>
    <title>The jQuery Example</title>
    
    <h2>jQuery-AJAX in FLASK. Execute function on button click</h2>  

    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"> </script>
    <script type=text/javascript> $(function() { $("#mybutton").click(function (event) { $.getJSON('/SomeFunction', { },
    function(data) { }); return false; }); }); </script> 
</head>

<body>        
        <input type = "button" id = "mybutton" value = "Click Here" />
</body>    
    
</html>

test.py

from flask import Flask, jsonify, render_template, request
app = Flask(__name__)


@app.route('/')
def index():
    return render_template('index.html')
    
@app.route('/SomeFunction')
def SomeFunction():
    print('In SomeFunction')
    return "Nothing"



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