Returns the content of a cached resource.

        Args:
            url: The url of the resource

        Returns:
            The content of the cached resource or None if not in the cache

def get_content(self, url):
        """Returns the content of a cached resource.

        Args:
            url: The url of the resource

        Returns:
            The content of the cached resource or None if not in the cache
        """
        cache_path = self._url_to_path(url)
        try:
            with open(cache_path, 'rb') as f:
                return f.read()
        except IOError:
            return None