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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def open(self, url, mode='rb', reload=False, filename=None):
 """Open a file, downloading it first if it does not yet exist. Unlike when you call a loader directly like ``my_loader()``, this ``my_loader.open()`` method does not attempt to parse or interpret the file; it simply returns an open file object. The ``url`` can be either an external URL, or else the path to a file on the current filesystem. A relative path will be assumed to be relative to the base directory of this loader object. If a URL was provided and the ``reload`` parameter is true, then any existing file will be removed before the download starts. The ``filename`` parameter lets you specify an alternative local filename instead of having the filename extracted from the final component of the URL. """

        if '://' not in url:
            path_that_might_be_relative = url
            path = os.path.join(self.directory, path_that_might_be_relative)
            return open(path, mode)
        if filename is None:
            filename = urlparse(url).path.split('/')[-1]
        path = self.path_to(filename)
        if reload and os.path.exists(path):
            os.remove(path)
        if not os.path.exists(path):
            download(url, path, self.verbose)
        return open(path, mode)