def onShortcutUnindentWithBackspace(self):
        """Backspace pressed, unindent
        """
        assert self._qpart.textBeforeCursor().endswith(self.text())

        charsToRemove = len(self._qpart.textBeforeCursor()) % len(self.text())
        if charsToRemove == 0:
            charsToRemove = len(self.text())

        cursor = self._qpart.textCursor()
        cursor.setPosition(cursor.position() - charsToRemove, QTextCursor.KeepAnchor)
        cursor.removeSelectedText()
def draw():
    global theta
    context.clearRect(0, 0, canvas.width, canvas.height)
    line1.drawMe(context)
    line2.drawMe(context)
    line3.drawMe(context)
    #triangle1.drawMe(context)
    #triangle2.drawMe(context)
    theta += dx
    p2.x = p1.x + line1.length*math.cos(theta*degree)
    p2.y = p1.y - line1.length*math.sin(theta*degree)
    p3.x, p3.y = triangle2.setPPSS(p2,p4,link2_len,link3_len)
    p1.tag(context)