code: def visit_Import(self, node):
          
          for alias in node.names:
              alias_name = tuple(alias.name.split('.'))
              self.imports.add(alias_name[0])
              if alias.asname:
                  self.symbols[alias.asname] = alias_name
              else:
                  self.symbols[alias_name[0]] = alias_name[:1]
              self.update = True
          return None
docs: Register imported modules and usage symbols.