import xml.etree.ElementTree as ET


def is_valid(resource, file):
    """Check if the HTTP response is an ATOM feed."""

    with open(file.name, "rb") as f:
        try:
            xml = ET.parse(f).getroot()

            if xml.tag == "{http://www.w3.org/2005/Atom}feed":
                return True
            else:
                resource["error"] = (
                    "Root element is not {http://www.w3.org/2005/Atom}feed"
                )
                return False
        except Exception as e:
            resource["error"] = str(e)
            return False