Python Flask - Processing input obtained from front-end in the back-end

Question

this is more of a question about where to find how I would do this rather than asking how to do this. I'm sure this is well covered, I'm just struggling to articulate the correct term which I could use to Google and find out the answer.

Anyway - I have a Python Flask web application. On a web page, there is an input box which requests user input. What I would like to happen, is for some magic to happen with the user input in the background. In my own scenario, I would like to take a URL, then use bs4 to pick off what I need and display this on the web page.

For simplicity, I'll ask for something for simple and I can then build on it from there: if I were to request the user to specify a number then press 'Submit', how could I multiply the number by 10?

If my code for the form was index.html :

<form class="form-horizontal" role="form" method="post" action="/">
    {{ form.csrf_token }}
        <fieldset>
            <div class="form-group">
                <label for="GetNum" class="col-lg-2 control-label">Enter Number</label>
                    <div class="col-lg-6">
                        <input type="text" id="GetNum" name="GetNum" class="form-control" value="">
                    </div>
                <input class="btn btn-success" type="submit" value="Calculate">
            </div>
        </fieldset>
</form>

I noticed that I can get the input to print to a paragraph by <p>form.request.GetNum</p> .

Now for this question's example, the code for the backend functionality will be:

import math
GetNum = 10  #should be form.request.GetNum value
CalcResult = GetNum*1000
print CalcResult  #  or {{ CalcResult.data }} or something in index.html

My Controller ( app.py ) looks like:

@app.route('/', methods=['GET', 'POST'])
@login_required
    def home():
    error = None
    form = PostForm(request.form)  # unrelated to question, but will this clash?
    if .. :
        do something
        return redirect(..)
    else:
        do something else..
        return render_template(..)       

My worry is that the home function will end up having a mass of code if I have to put the math function in there. So tl;dr, how would I implement a back end function within my code? (or please provide me with material to read, thank you!)

One other thing is I already have a form on my '/' page, will I have to rename the forms like form1 form2 because they will clash or will it be OK?

Answer 1

Elsewhere in your code base, either in the same file, or more likely a module or package you could define that complicated task. Lets create a simple module complicated.py in the same directory as your other code, that then defines the complicated task:

def do_really_complicated_thing(info):
    # lots of complicated steps
    return really_complicated_data

Then in our view code, we can just use that instead of having it embedded:

from complicated import do_really_complicated_thing

@app.route('/', methods=['GET', 'POST'])
@login_required
def home():
    error = None
    form = PostForm(request.form)
    if form.validate_on_submit() :
        info = form.info.data
        complicated_task = do_really_complicated_thing(info)
        return render_template('something', results=complicated_task)
 

So, in short-- the terms you're looking for is packages and modules, they help your code be neater and reusable.

As for clashing forms— you can just target the form to post to a specific route which just handles that form, which is much cleaner then then having to validate/parse different forms in a single route.