code: def name_check(self, original, loc, tokens):
          
          internal_assert(len(tokens) == 1, "invalid name tokens", tokens)
          if self.strict:
              self.unused_imports.discard(tokens[0])
          if tokens[0] == "exec":
              return self.check_py("3", "exec function", original, loc, tokens)
          elif tokens[0].startswith(reserved_prefix):
              raise self.make_err(CoconutSyntaxError, "variable names cannot start with reserved prefix " + reserved_prefix, original, loc)
          else:
              return tokens[0]
docs: Check the given base name.