docs: def isfile(self, path=None, client_kwargs=None, assume_exists=None):
          """
          Return True if path is an existing regular file.
  
          Args:
              path (str): Path or URL.
              client_kwargs (dict): Client arguments.
              assume_exists (bool or None): This value define the value to return
                  in the case there is no enough permission to determinate the
                  existing status of the file. If set to None, the permission
                  exception is reraised (Default behavior). if set to True or
                  False, return this value.
  
          Returns:
              bool: True if file exists.
          """
          relative = self.relpath(path)
          if not relative:
              # Root always exists and is a directory
              return False
  
          if path[-1] != '/' and not self.is_locator(path, relative=True):
              return self.exists(path=path, client_kwargs=client_kwargs,
                                 assume_exists=assume_exists)
          return False