code: def save(filters='*.*', text='Save THIS, facehead!', default_directory='default_directory', force_extension=None):
      
      # make sure the filters contains "*.*" as an option!
      if not '*' in filters.split(';'): filters = filters + ";;All files (*)"
      
      # if this type of pref doesn't exist, we need to make a new one
      if default_directory in _settings.keys(): default = _settings[default_directory]
      else:                                     default = ""
      
      # pop up the dialog
      result = _qtw.QFileDialog.getSaveFileName(None,text,default,filters)
      
      # If Qt5, take the zeroth element
      if _s._qt.VERSION_INFO[0:5] == "PyQt5": result = result[0]    
      
      # Make sure it's a string
      result = str(result)
      
      # Enforce the extension if necessary
      if  not force_extension == None:
              
          # In case the user put "*.txt" instead of just "txt"
          force_extension = force_extension.replace('*','').replace('.','')
  
          # If it doesn't end with the right extension, add this.
          if not _os.path.splitext(result)[-1][1:] == force_extension:
              result = result + '.' + force_extension
  
      if result == '': return None
      else:
          _settings[default_directory] = _os.path.split(result)[0]
          return result
docs: Pops up a save dialog and returns the string path of the selected file.
      
      Parameters
      ----------
      filters='*.*'
          Which file types should appear in the dialog.
      text='Save THIS, facehead!'
          Title text for the dialog.
      default_directory='default_directory'
          Key for the spinmob.settings default directory. If you use a name, e.g.
          'my_defaultypoo', for one call of this function, the next time you use
          the same name, it will start in the last dialog's directory by default.
      force_extension=None
          Setting this to a string, e.g. 'txt', will enforce that the filename 
          will have this extension.