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This question could be a duplicate but I have checked all the answers of such related questions and I haven't been able to solve it.

I am trying to get the value from a dropdown menu which consists of numbers. Then I want to compare the numbers with a value and display a text based on the comparison.

Eg 

if value_selected_from_dropdown >3
 display text

I am unable to get the text to display or even print the value of the option selected.

Here is the python file, web_plants.py

from flask import Flask, render_template,request, redirect, url_for

app = Flask(__name__)

def template(title = "HELLO!", text = ""):
    templateDate = {
        'text' : text
        }
    return templateDate

@app.route("/threshold", methods=['POST'])
def threshold():
        tvalue= (request.form.get['tvalue']) #get value from dropdown
        msg= ""
        if tvalue>3:
          msg= "rating above 3"
         templateData = template(text = msg) #display text using template()
        #templateData = template(text = tvalue) #tried to print the value selected
        return render_template('index.html', **templateData)

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80, debug=True)

index.html:

<!DOCTYPE HTML>
<html>

<head>
 <link rel="stylesheet" type="text/css" href="{{ url_for('static',filename='style.css')}}" />
</head>

<body>

 <h2> {{ text }} </h2>
<form action= "{{ url_for('threshold') }}" method="post>"
             <p>
             <select name= 'tvalue'>
                 <option value="10">10</option>
                 <option value="11">11</option>
                 <option value="15">15</option>
                 <option value="2">2</option>
                 <option value="1">1</option>
              </select>
              </p>
    </form>
 </body>
</html>
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2
  • 1
    method="post>" is a typo. Should be method="post"> Commented Apr 3, 2018 at 13:03
  • @noslenkwah Thanks for pointing that out. Commented Apr 3, 2018 at 13:09

2 Answers 2

Reset to default
3

There are several ways to achieve this. Either you can give logic to the template itself or you can add the logic in the function threshold.

index.html

<h2> {{text}} </h2>
<form action= "{{ url_for('threshold') }}" method="POST">

     <select name= 'tvalue'>
      {% for tvalue in tvalues %}
        {% if selected_tvalue == tvalue %}
            <option value="{{ tvalue }}" selected='selected'>{{ tvalue }}</option>
        {% else %}
             <option value="{{ tvalue }}" >{{ tvalue }}</option>
        {% endif %}
      {% endfor %}

      </select>

     <input type="submit" value="Submit" />
</form>

OR,

{% if selected_tvalue > 3 %}
    <h2> Selected value is greater than 3 </h2>
{% else %}
     <h2> Selected value is less than or equal to 3 </h2>
{% endif %}   
<form action= "{{ url_for('threshold') }}" method="POST">

     <select name= 'tvalue'>
      {% for tvalue in tvalues %}
        {% if selected_tvalue == tvalue %}
            <option value="{{ tvalue }}" selected='selected'>{{ tvalue }}</option>
        {% else %}
             <option value="{{ tvalue }}" >{{ tvalue }}</option>
        {% endif %}
      {% endfor %}

      </select>
    <input type="submit" value="Submit" />
</form>

server.py

def template(title = "HELLO!", text = ""):
    templateDate = {
        'text' : text,
        'tvalues' : getTValues(),
        'selected_tvalue' : -1
    }
    return templateDate

def getTValues():
    return (10, 11, 15, 2, 1) 

@app.route("/threshold", methods=['POST', 'GET'])
def threshold():
    tvalue= -1 #default value
    msg = ''
    if request.method == "POST":            
        tvalue = int(request.form['tvalue'])
        if tvalue> 3:
            msg= "rating above 3"

    #generating template data
    templateData = template(text = msg)
    templateData['selected_tvalue'] = tvalue 

    return render_template('index.html', **templateData)

Then access your form at path /threshold. I hope it helps.

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3 Comments

I owe you the credits for helping me implement an important functionality in my final year project related to IoT and Raspberry Pi. The codes I posted provided just a basic and "simplified" means to get a threshold value to compare with sensor values I am getting(not added in the codes I posted). Based on the comparison(if tvalue> 3:), a bulb will turn on and off. Thank you so much for taking the time to write the answer :)
Hello, I need to have this function run as a background task so that when a user clicks on the Submit button, the value is constantly being checked by the if operator. Can you please help with it? Because I am getting working outside of request context when I tried to get it working through some ways
I posted a question on it here: stackoverflow.com/questions/49688824/…
1

In your html after your drop down block you may need something like

 <input type="submit">

which will trigger the submit. I am not sure, selecting a value alone triggers the form submit.

By the way where are you rendering your page initially ? I would have something like:

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

in the python code. There to get the value, I would try

tvalue= request.args.get('tvalue')

Well not 'form' but 'args', and normal brackets instead of squared ones. Finally the function where you are going to handle that 'templateData' might be missing too.

last note: you might need GET method too:

@app.route("/threshold", methods=['GET', 'POST'])
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1 Comment

I am rendering it initially at index.html.. I just omitted that part in the codes I posted

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