[Qgis-developer] PyQt4.QtCore.QVariant represents a mapped type and cannot be instantiated

[Gary Sherman]

On 10/1/14 12:55 PM, Mark Coletti wrote:
> I'm writing a qgis python plugin and have encountered a curious
> problem.  I've successfully tested the plugin's dialog standalone via
> ipython.  However, I get the following error when I try to execute the
> same code from within qgis: "PyQt4.QtCore.QVariant represents a mapped
> type and cannot be instantiated".
>

Your answer is here: 
http://hub.qgis.org/wiki/quantum-gis/Python_plugin_API_changes_from_18_to_20

QVariant is no longer present in QGIS since we use the sip 2.0 api.
Use regular strings rather than a QVariant.

> The error occurs from within a QAbstractTableModel subclass,
> specifically the headerData function, which is given below:
>
>      def headerData(self, section, orientation, role):
>          if role == Qt.DisplayRole :
>              if orientation == Qt.Horizontal :
>                  return QVariant(self.headers[section])
>              elif orientation == Qt.Vertical :
>                  return QVariant(self.events[section].categoryID)
>          return QVariant()
>
> As far as I can tell, that's pretty much textbook PyQt.  I've found a
> similar problem
> <http://stackoverflow.com/questions/10382025/qvariant-in-qcombobox-python-2-vs-python-3>,
> but that was a python 2 vs. 3 scenario, and this is all within the
> python 2.7.1 domain.
>
> I've tried to code up a workaround where I just return empty strings and
> that leads to all sorts of havok.  The table is rendered, but the header
> columns are missing and there are undesired check boxes in all the table
> cells.
>
> Has anyone else encountered this problem?  Or otherwise knows what's
> going on?
>
> Cheers!
>
> Mark
> --
> mcoletti at gmail.com <mailto:mcoletti at gmail.com>
>
>
>
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Gary Sherman

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