<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def retrieve_file_from_url(url):
 """ Retrieve a file from an URL Args: url: The URL to retrieve the file from. Returns: The absolute path of the downloaded file. """

    try:
        alias_source, _ = urlretrieve(url)
        # Check for HTTPError in Python 2.x
        with open(alias_source, 'r') as f:
            content = f.read()
            if content[:3].isdigit():
                raise CLIError(ALIAS_FILE_URL_ERROR.format(url, content.strip()))
    except Exception as exception:
        if isinstance(exception, CLIError):
            raise

        # Python 3.x
        raise CLIError(ALIAS_FILE_URL_ERROR.format(url, exception))

    return alias_source