code: def simplefilter(action, category=Warning, lineno=0, append=0):
      
      assert action in ("error", "ignore", "always", "default", "module",
                        "once"), "invalid action: %r" % (action,)
      assert isinstance(lineno, int) and lineno >= 0, \
             "lineno must be an int >= 0"
      item = (action, None, category, None, lineno)
      if append:
          filters.append(item)
      else:
          filters.insert(0, item)
docs: Insert a simple entry into the list of warnings filters (at the front).
  
      A simple filter matches all modules and messages.
      'action' -- one of "error", "ignore", "always", "default", "module",
                  or "once"
      'category' -- a class that the warning must be a subclass of
      'lineno' -- an integer line number, 0 matches all warnings
      'append' -- if true, append to the list of filters