title: AttributeError: 'tuple' object has no attribute 'drivername' using Flask SqlAlchemy
body: <p>I'm trying to connect to a MySQL database using Flask-SqlAlchemy, here's my parameter :</p>
  
  <pre><code>SQLALCHEMY_DATABASE_URI = 'mysql://root:pass@127.0.0.1/database?charset=utf8'
  </code></pre>
  
  <p>But when I go to the url, I get this error :</p>
  
  <blockquote>
    <p>AttributeError: 'tuple' object has no attribute 'drivername'</p>
  </blockquote>
  
  <p>If I change the <code>SQLALCHEMY_DATABASE_URI</code> to <code>sqlite:///db.sqlite</code>, it works correctly.</p>
  
  <p>What am I missing ?</p>
  
  <p>Note: I also tried <code>mysql+mysqldb://</code>, without any luck.</p>