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 setSAS(self, lenp3, ap2, lenp1):
        self.lenp3 = lenp3
        self.ap2 = ap2
        self.lenp1 = lenp1
        self.lenp2 = math.sqrt((self.lenp3 * self.lenp3 + self.lenp1 * self.lenp1) - 2* self.lenp3 * self.lenp1 * math.cos(self.ap2))
        #等於 SSS(AB, BC, CA)