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 r…

Accepted Answer

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 %}
```

flask form.validate_on_submit() fails using wtforms

Solution

Problem