title: Why doesn't QCalendarWidget.setDateTextFormat(QDate(), ...) work?
body: <p>I'm using PyQt 4.4.3.</p>
  <p>I've got this code, which should clear all formats in the <code>QCalendarWidget</code>:</p>
  <pre><code>cal.setDateTextFormat(QDate(), QDateTextFormat())
  </code></pre>
  <p>According to <a href="http://doc.trolltech.com/4.4/qcalendarwidget.html#setDateTextFormat" rel="nofollow noreferrer">the documentation</a> this should work:</p>
  <blockquote>
  <p><strong><code>QCalendarWidget::setDateTextFormat(QDate &amp;date, QTextCharFormat &amp;format)</code></strong><br />
  If date is <code>null</code>, all date formats are cleared.</p>
  <p><strong><code>QDate::QDate()</code></strong><br />
  Constructs a <code>null</code> date. Null dates are invalid.</p>
  </blockquote>
  <p>I've tried narrowing down the problem like this:</p>
  <pre><code>QDate().isNull()
  True
  cal.dateTextFormat()
  {PyQt4.QtCore.QDate(-4713, 1, 1): PyQt4.QtGui.QTextCharFOrmat object}
  </code></pre>
  <p>Obviously, <code>QDate()</code> is interpreted as being in the year -4713 instead of being <code>null</code>.</p>
  <p>Any idea what I need to change to make it work?</p>
  <p><em>Edit:</em> The problem is, that the calendar isn't reset using this method.</p>