code: def use(name):
      
      global toolkit, family
  
      name = name.lower()
  
      if name.startswith('choose'):
          pass
  
      elif name.startswith('qt') or name.startswith('pyside'):
          family = 'qt'
          if name == 'qt':
              name = 'qt4'
          assert name in ('qt4', 'pyside', 'qt5'), \
              ToolKitError("ToolKit '%s' not supported!" % (name))
  
      elif name.startswith('gtk'):
          # default for "gtk" is gtk3
          if name in ('gtk', 'gtk3'):
              name = 'gtk3'
              family = 'gtk3'
          elif name in ('gtk2',):
              family = 'gtk'
          assert name in ('gtk2', 'gtk3'), \
              ToolKitError("ToolKit '%s' not supported!" % (name))
  
      elif name.startswith('tk'):
          family = 'tk'
          assert name in ('tk', ), \
              ToolKitError("ToolKit '%s' not supported!" % (name))
  
      elif name.startswith('pg'):
          family = 'pg'
          assert name in ('pg', ), \
              ToolKitError("ToolKit '%s' not supported!" % (name))
  
      else:
          ToolKitError("ToolKit '%s' not supported!" % (name))
  
      toolkit = name
docs: Set the name of the GUI toolkit we should use.