HtmlEditor should display only a line at first, with the height just enough to hold a line, not bigger, not smaller. As the user inputs more lines, the height of HtmlEditor will get bigger too. I tried to use self.page().mainFrame().contentsSize().height() as follows, it didn't work. I tried to replace self.page().mainFrame().contentsSize().height() with self.fontSize + self.contentsMargins().top() + self.contentsMargins().bottom(). But self.contentsMargins().top() and self.contentsMargins().bottom() are always zero. I don't know why. How to do the trick?
Qt Code: 
  1. class HtmlEditor(QWebView):
  2.     def __init__(self, fontSize):
  3.         super().__init__()
  4.         self.fontSize = fontSize
  5.         self.page().setContentEditable(True)
  6.         self.page().contentsChanged.connect(self.sizeChange)
  7.         self.setupFont()
  8.         self.sizeChange()
  9.  
  10.     def setupFont(self):
  11.         self.htmlEditorSettings = self.settings()
  12.         self.htmlEditorSettings.setFontSize(QWebSettings.DefaultFontSize, self.fontSize)
  13.  
  14.     def sizeChange(self):
  15.         docHeight = self.page().mainFrame().contentsSize().height()
  16.         self.setFixedHeight(docHeight)
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