I am trying to upload files using the [flask-uploads](http://pythonhosted.org/Flask-Uploads/) extension.
The problem is that, each time it seems I find a solution, I fund an other problem, and I feel the documentation cryptic.

Here is the code :

```
from flask.ext.uploads import UploadSet, IMAGES, configure_uploads 
import os
from werkzeug import secure_filename

photos = UploadSet('photos', IMAGES)
configure_uploads(app, photos)

@app.route('/edit_book', methods = ['GET', 'POST'])
def edit_book():
form = BookForm()
if form.validate_on_submit():
            b.summary = form.summary.data
    if request.method == 'POST':
        try:
            secure_filename = photos.save(request.files['cover'])
        except:
            print 'not ok'
            db.session.add(b)
    db.session.commit()
    return redirect('/admin')
return render_template('edit_book.html', title = 'Add a book', form = form )

```

The current error give just :

```
KeyError: 'images'.

```

I have nothing more ! Does any one issue in using this extension, as I find no suitable piece of code anywhere that give a full solution (from the start of an upload to the saving of the file in a folder).

Thank you in advance for your help.

Template code
-------------

```
<!-- extend from admin layout -->
{% extends "admin.html" %}

{% block content %}
 <form action="" method="post" name="edit_book" enctype="multipart/form-data">
{{form.hidden_tag()}}

{% if dico %}
 <h1>Ajouter le livre <i>{{dico.title}}</i> à la base de données</h1>
{% else %}
{% set dico = [] %}
 <h1>Ajouter un livre à la base de données</h1>
 {% endif %}
<p>Titre (obligatoire) :    {{form.title(value=dico.title)}}</p>
<p>ISBN 13 (EAN) :      {{form.ean(value=dico.EAN)}}</p>
<p>ISBN :           {{form.isbn(value=dico.ISBN)}}</p>
<p>Maison d'édition :       {{form.publisher(value=dico.publisher)}}</p>
<p>epaisseur (cm) :     {{form.thickness(value=dico.thickness)}}</p>
<p>longueur (cm) :      {{form.length(value=dico.length)}}</p>
<p>largeur (cm) :       {{form.width(value=dico.width)}}</p>
<p>masse (kg) :         {{form.mass(value=dico.mass)}}</p>
<p>Nombre de pages :        {{form.numberofpages(value=dico.pages)}}</p>
<p>Couverture du livre :    {{form.cover(value=dico.img)}}</p>
<p>Quatrième de couverture :    {{form.summary(cols="35", rows="20")|safe}}</p>
<p><input type="submit" value="Envoyez"></p>
</form>
{% endblock %}

```

Error Stacktrace
----------------

```
* Running on http://127.0.0.1:5000/
* Restarting with reloader
127.0.0.1 - - [22/Jul/2013 15:16:18] "POST /edit_book HTTP/1.1" 500 -
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1701, in __call__
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1689, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1687, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1360, in    full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1358, in  full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1344, in  dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/stephane/git/biblib-flask/app/views.py", line 117, in edit_book
if form.validate_on_submit():
File "/usr/local/lib/python2.7/dist-packages/flask_wtf/form.py", line 125, in  validate_on_submit
return self.is_submitted() and self.validate()
 File "/usr/local/lib/python2.7/dist-packages/wtforms/form.py", line 265, in validate
return super(Form, self).validate(extra)
 File "/usr/local/lib/python2.7/dist-packages/wtforms/form.py", line 130, in validate
if not field.validate(self, extra):
 File "/usr/local/lib/python2.7/dist-packages/wtforms/fields/core.py", line 176, in  validate
 stop_validation = self._run_validation_chain(form, chain)
 File "/usr/local/lib/python2.7/dist-packages/wtforms/fields/core.py", line 196, in _run_validation_chain
 validator(form, self)
 File "/usr/local/lib/python2.7/dist-packages/flask_wtf/file.py", line 69, in __call__
if not self.upload_set.file_allowed(field.data, field.data.filename):
 File "/usr/local/lib/python2.7/dist-packages/Flask_Uploads-0.1.3-    py2.7.egg/flaskext/uploads.py", line 346, in file_allowed
 return self.extension_allowed(extension(basename))
 File "/usr/local/lib/python2.7/dist-packages/Flask_Uploads-0.1.3-py2.7.egg/flaskext/uploads.py", line 356, in extension_allowed
 return ((ext in self.config.allow) or
 File "/usr/local/lib/python2.7/dist-packages/Flask_Uploads-0.1.3-py2.7.egg/flaskext/uploads.py", line 308, in config
 return current_app.upload_set_config[self.name]
 KeyError: 'images'
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?    __debugger__=yes&cmd=resource&f=style.css HTTP/1.1" 200 -
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?__debugger__=yes&cmd=resource&f=jquery.js HTTP/1.1" 200 -
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?__debugger__=yes&cmd=resource&f=debugger.js HTTP/1.1" 200 -
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?__debugger__=yes&cmd=resource&f=ubuntu.ttf HTTP/1.1" 200 -
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -
 127.0.0.1 - - [22/Jul/2013 15:16:18] "GET /edit_book?__debugger__=yes&cmd=resource&f=source.png HTTP/1.1" 200 -

```

I just checked the code more largely, and find only one thing that is exactly 'images' :
a validator in the forms.

```
 from flaskext.uploads import UploadSet, IMAGES
 images = UploadSet("images", IMAGES)

 class BookForm(Form):
    summary = TextAreaField('summary', [validators.optional()])
cover = FileField("cover", [validators.optional(),file_allowed(images, "Images only!")])

```