QTableWidget display certain decimals like excel

Question

My question is about the way the QTableWidget displays the cell values.

I'd like for the cell to show only three decimals when it's not being edited and show the full value when you double click for editing.

---

I am doing calculations in background and then setting the cell value afterwards.

V_D = 3/0.7
self.TableWidget.setItem(0, 0, QTableWidgetItem(str(V_D)))

Similar to the way excel formats the cell to show certain number of digits.

Full Value:

Display Value:

How would I go about doing this?

Answer 1

The solution is to use a delegate and override the paint method that is responsible for showing what looks in normal state, I have built the following class based on the above.

class FloatDelegate(QItemDelegate):
    def __init__(self, decimals, parent=None):
        QItemDelegate.__init__(self, parent=parent)
        self.nDecimals = decimals

    def paint(self, painter, option, index):
        value = index.model().data(index, Qt.EditRole)
        try:
            number = float(value)
            painter.drawText(option.rect, Qt.AlignLeft, "{:.{}f}".format(number, self.nDecimals))
        except :
            QItemDelegate.paint(self, painter, option, index)

In your case you should use it as follows:

self.TableWidget.setItemDelegate(FloatDelegate(3))

Example:

if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    w = QTableWidget()
    w.setColumnCount(8)
    w.setRowCount(8)
    for i in range(w.rowCount()):
        for j in range(w.columnCount()):
            number = (i+1)/(j+1)
            w.setItem(i, j, QTableWidgetItem(str(number)))
    w.setItemDelegate(FloatDelegate(3, w))
    w.show()
    sys.exit(app.exec_())

Screenshots:

Plus:

By Row o Column:

#only column 2
setItemDelegateForColumn(2, FloatDelegate(3))
#only row 2
setItemDelegateForRow(2, FloatDelegate(3))

If you want to apply only to cell 2,3

def paint(self, painter, option, index):
   if index.row() == 2 and index.column() == 3:
        value = index.model().data(index, Qt.EditRole)
        try:
            number = float(value)
            painter.drawText(option.rect, Qt.AlignLeft, "{:.{}f}".format(number, self.nDecimals))
        except :
            QItemDelegate.paint(self, painter, option, index)
    else:
        QItemDelegate.paint(self, painter, option, index)

Update:

• QStyledItemDelegate:

  from math import log10
  
  class FloatDelegate(QStyledItemDelegate):
      def __init__(self, decimals, parent=None):
          super(FloatDelegate, self).__init__(parent=parent)
          self.nDecimals = decimals
  
      def displayText(self, value, locale):
          try:
              number = float(value)
          except ValueError:
              return super(FloatDelegate, self).displayText(value, locale)
          else:
              precision = log10(number) + 1 + self.nDecimals
              return locale.toString(number, f='f', prec=precision)