How to remove unused function parameters in shutil

问题:

In this question, an answer to how to remove read-only files is presented. It's super effective but requires having unused parameters. In this other question it was asked how to tell pylint that multiple non-adjacent parameters are unused without adding a specific comment (e.g., by using _). Many of the answers were approximately "ZOMG YOU'RE DESIGNING IT WRONG" so I promised I would put up an example where this is needed and out of my control. Here is that example.

shutil.rmtree(self._temp_dir, onerror=del_rw)

def del_rw(action, name, exc):
    os.chmod(name, stat.S_IWRITE)
    os.remove(name)

The "answer" so that pylint would not complain about action and exc is to

shutil.rmtree(self._temp_dir, onerror=del_rw)

def del_rw(_action, name, _exc):
    os.chmod(name, stat.S_IWRITE)
    os.remove(name)

but the new question is, how to do this without having _action or _exc as parameters?

回答1:

As discussed in the comments, you cannot just ignore action, and exc because rmtree will pass those arguments to the callback. From the python docs:

If onerror is provided, it must be a callable that accepts three parameters: function, path, and excinfo.

That being said, you have a couple of options:

• You can prefix the callback with a cb_ (see pylint docs on this as well), turning your function into:

  shutil.rmtree(self._temp_dir, onerror=cb_del_rw)
  
  def cb_del_rw(action, name, exc):
      os.chmod(name, stat.S_IWRITE)
      os.remove(name)
  

• You can use keyword arguments (you could also use *args, but I find this approach more readable):

  shutil.rmtree(self._temp_dir, onerror=del_rw)
  
  def del_rw(**kwargs):
      name = kwargs['name']
      os.chmod(name, stat.S_IWRITE)
      os.remove(name)