<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate(self, qstr, editing=True):
 """Reimplemented to avoid formatting actions"""

        valid = self.is_valid(qstr)
        if self.hasFocus() and valid is not None:
            if editing and not valid:
                # Combo box text is being modified: invalidate the entry
                self.show_tip(self.tips[valid])
                self.valid.emit(False, False)
            else:
                # A new item has just been selected
                if valid:
                    self.selected()
                else:
                    self.valid.emit(False, False)