show a file dialog

def call(self):
        '''show a file dialog'''
        from MAVProxy.modules.lib.wx_loader import wx

        # remap flags to wx descriptors
        flag_map = {
            'open': wx.FD_OPEN,
            'save': wx.FD_SAVE,
            'overwrite_prompt': wx.FD_OVERWRITE_PROMPT,
        }
        flagsMapped = map(lambda x: flag_map[x], self.flags)

        #need to OR together the elements of the flagsMapped tuple
        if len(flagsMapped) == 1:
            dlg = wx.FileDialog(None, self.title, '', "", self.wildcard, flagsMapped[0])
        else:
            dlg = wx.FileDialog(None, self.title, '', "", self.wildcard, flagsMapped[0]|flagsMapped[1])
        if dlg.ShowModal() != wx.ID_OK:
            return None
        return "\"" + dlg.GetPath().encode('utf8') + "\""