Must start with http:// or https:// and contain JUST a URL

def is_url(value):
    "Must start with http:// or https:// and contain JUST a URL"
    if not isinstance(value, str):
        return False
    if not value.startswith('http://') and not value.startswith('https://'):
        return False
    # Any whitespace at all is invalid
    if whitespace_re.search(value):
        return False
    return True