code: def get_main_pattern(self, directory):
          
          return os.path.join(directory, format(
              '{prefix}{program_name}.{extension}',
              extension=self.filename_extension.lstrip('.'),
              program_name=self.program_name,
              prefix=self.get_prefix(directory),
          ))
docs: Get the :func:`~glob.glob()` pattern to find the main configuration file.
  
          :param directory: The pathname of a base directory (a string).
          :returns: A filename pattern (a string).
  
          This method generates a pattern that matches a filename based on
          :attr:`program_name` with the suffix :attr:`filename_extension` in the
          given base `directory`. Here's an example:
  
          >>> from update_dotdee import ConfigLoader
          >>> loader = ConfigLoader(program_name='update-dotdee')
          >>> [loader.get_main_pattern(d) for d in loader.base_directories]
          ['/etc/update-dotdee.ini',
           '~/.update-dotdee.ini',
           '~/.config/update-dotdee.ini']