flask form.validate_on_submit() fails using wtforms

Question

Using @dirn's suggestions, the validation error does not display anymore, but it still seems to fail as neither the print statement in the root() function displays/runs nor does the new form.errors show.

App Code:

#!/usr/bin/env python

import cherrypy
import os
from flask import Flask, render_template, redirect, url_for, session, request, flash, abort, Markup
from flask.ext.bootstrap import Bootstrap
from sybload import funcs, forms

app = Flask(__name__)
app.debug = True
app.config['SECRET_KEY'] = os.urandom(24)
app.config['CSRF_ENABLED'] = True
bootstrap = Bootstrap(app)

dataserver_info = funcs.get_dataserver_info()
dataservers = funcs.get_dataservers(dataserver_info)

@app.route('/', methods=['GET', 'POST'])
def root():
    session.clear()
    form = forms.DataServersForm()
    form.dataserver.choices = zip(dataservers, dataservers)
    if form.validate_on_submit():
        session['dataserver'] = form.dataserver.data
        # print statement below never runs
        print session['dataserver'], form.dataserver.data
        return redirect(url_for('login'))
    return render_template('root.html', title='Sybase Load App', form=form)

def run_server():
    cherrypy.tree.graft(app, '/')
    cherrypy.config.update({
        'log.access_file': 'logs/access.log',
        'log.error_file': 'logs/errors.log',
        'engine.autoreload_on': True,
        'log.screen': True,
        'server.socket_host': '0.0.0.0',
        'server.socket_port': 5000,
        'tools.sessions.on': True,
        'tools.sessions.secure': True,
        'tools.sessions.httponly': True
    })
    cherrypy.engine.start()
    cherrypy.engine.block()

if __name__ == '__main__':
    run_server()

Template (jinja2):

    {% block body %}
    <form method='post' action='{{ url_for('login') }}'>
        {{ form.hidden_tag() }}

        {{ form.dataserver.label }}<br>
        {{ form.dataserver }}<br><br>

        {{ form.submit }}
    </form>
    <!-- Below never displays -->
    {% if form.errors %}
        failed validation
    {% endif %}
    {% endblock %}

Form:

from flask.ext.wtf import Form
from wtforms import StringField, PasswordField, SelectField, SelectMultipleField, SubmitField, BooleanField
from wtforms.validators import Required
import funcs

class DataServersForm(Form):
    dataserver = SelectField('Dataservers', validators=[Required()])
    submit = SubmitField('Submit')

Solution

You call form.validate() everytime someone visits '/'. When the request is a GET, there is no form data causing validation to fail. You only want to try to validate the form when the request is a POST.

One way to do that is to check the request's method.

if request.method == 'POST':
    if form.validate():
        session['dataserver'] = ds = form.dataserver.data
        return redirect(url_for('login'))
    else:
        flash('Failed validation')

Another common way to do this is with validate_on_submit. It handles checking for POSTs as well as validating the form.

if form.validate_on_submit():
    session['dataserver'] = ds = form.dataserver.data
    return redirect(url_for('login'))

Here you'd lose your ability to flash your 'validation failed' message. That may be acceptable, though, because you can check for form errors in your template.

{% if form.errors %}
    failed validation
{% endif %}

UPDATE

If you want to see the errors (which you may not), you can print them in the template instead of the generic "failed validation" message.

{% if form.errors %}
    {{ form.errors }}
{% endif %}

Comments

[bhudson]

After applying both of your suggestions, I believe there is still something wrong. The session['dataserver'] is never set properly. @app.route('/', methods=['GET', 'POST']) def root(): session.clear() form = forms.DataServersForm() form.dataserver.choices = zip(dataservers, dataservers) if form.validate_on_submit(): session['dataserver'] = form.dataserver.data print session['dataserver'], form.dataserver.data return redirect(url_for('login')) return render_template('root.html', title='Sybase Load App', form=form)

[dirn]

Code doesn't work so well in comments, please update your question instead.

[dirn]

Have you tried inspecting form.errors to see if the form isn't validating?

[bhudson]

Yes. form.errors before form.validate_on_submit() yields an empty dict, while it never even runs (e.g. print form.errors) if it's inside the "if form.validate_on_submit():" block.

[dirn]

If form validation fails, nothing inside the if will happen. You need to check it after (outside) the if. One such place to do so would be in the template like I mentioned in the answer.

[bhudson]

Thanks for your help! I managed to fix the last issue. It was validating properly, but the statement "session['dataserver'] = form.dataserver.data" had to be changed to "session['dataserver'] = request.form['dataserver']". I'm not quite sure why (get vs. post maybe?). It makes me think I need "if request.method == 'POST' and form.validate_on_submit():" instead.

[bhudson]

Note: I also removed the "action='{{ url_for('login') }}'" line in my template.

[Admin]

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