<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _search_path(self, directory_name, filename):
 """Searches for a given file in the specified directory."""

        full_path = path.join(directory_name, filename)
        if path.exists(full_path):
            return full_path

        # Could not find the requested file in any of the directories
        return None