Flask, SQLAlchemy and Jinja2 - UnicodeDecodeError

Question

I have a web application that uses Flask, SQLAlchemy and WTForms, along with the necessary Flask extensions to make it all work. MySQL is using utf8_bin for all tables and columns.

I inserted some Chinese characters and phpMyAdmin displays them correctly but whenever I try to open a page I get the following exception:

UnicodeDecodeError: 'ascii' codec can't decode byte 0xe6 in position 0: ordinal not in range(128)

I understand I should decode('utf8') the fields I want to display but shouldn't this be handled by SQLAlchemy for me?

The only way I managed to make this work was by iterating through the list of results and doing something similar to:

object.property = object.property.decode('utf8')

But obviously this shouldn't have to be done by hand. What am I missing?

Update: SQLAlchemy mapping

class Thread(db.Model):

    __tablename__ = 'Thread'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.Unicode(255), nullable=False)
    body = db.Column(db.Text, nullable=True)
    date_created = db.Column(db.DateTime, nullable=False, default=datetime.now())
    created_by = db.Column(db.Integer, ForeignKey(User.id))
    user = relationship(User, backref='threads')
    display_hash = db.Column(db.Unicode(255), nullable=False, unique=True)
    display_name = db.Column(db.Unicode(255), nullable=True)
    nsfw = db.Column(db.Boolean, nullable=False, default=False)
    last_updated = db.Column(db.DateTime, nullable=False)

    def __init__(self, title=None, body=None, category_id=None, display_name=None):
        self.title = title
        self.body = body
        self.category_id = category_id
        self.display_name = display_name
        self.display_hash = custom_uuid()
        self.last_updated = self.date_created

    def __repr__(self):
        return u'<Thread %r>' % (self.title)

    def url_title(self):
        """ Generates an ASCII-only slug. """

        result = []
        for word in _punct_re.split(self.title.lower()):
            result.extend(unidecode(word).split())
        return unicode(u'-'.join(result))

Update: stack trace

`127.0.0.1 - - [06/Oct/2013 02:37:15] "GET /index HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/homedirectory/Projects/Assorted/Fruit Show/app/views.py", line 90, in index
    return render_template('index.html', threads=threads, pagination=pagination)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/templating.py", line 128, in render_template
    context, ctx.app)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/flask/templating.py", line 110, in _render
    rv = template.render(context)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/jinja2/environment.py", line 969, in render
    return self.environment.handle_exception(exc_info, True)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/jinja2/environment.py", line 742, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/homedirectory/Projects/Assorted/Fruit Show/app/templates/index.html", line 1, in top-level template code
    {% extends 'base.html' %}
  File "/Users/homedirectory/Projects/Assorted/Fruit Show/app/templates/base.html", line 50, in top-level template code
    {% block content %}
  File "/Users/homedirectory/Projects/Assorted/Fruit Show/app/templates/index.html", line 14, in block "content"
    <a href="{{ url_for('new_thread') }}/{{ thread.display_hash|safe }}/{{ thread.url_title()|safe }}">{{ thread.title|safe }}</a>
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/jinja2/filters.py", line 747, in do_mark_safe
    return Markup(value)
  File "/Users/homedirectory/.virtualenvs/fruitshow/lib/python2.7/site-packages/markupsafe/__init__.py", line 72, in __new__
    return text_type.__new__(cls, base)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe6 in position 0: ordinal not in range(128)`

Update: URL for project repo:

https://github.com/ruipacheco/fruitshow

Answer 1

The problem is with the MySQL driver I'm using.

I followed this answer and switching the column type from utf8_bin to utf8_general_ci did the trick.

Answer 2

A little suggestion for Slug field in your Models.

There is a Library called Webhelpers (https://pypi.python.org/pypi/WebHelpers), import that and your title will be automatically converted into the slug.

Install WebHelpers and then import urlify

from webhelpers.text import urlify
.
.
.
@property
def slug(self):
    return urlify(self.title)