'Unset a cookie with the given name (remove it from the
response).'

def unset_cookie(self, key, strict=True):

    existing = self.headers.getall('Set-Cookie')
    if ((not existing) and (not strict)):
        return
    cookies = Cookie()
    for header in existing:
        cookies.load(header)
    if isinstance(key, text_type):
        key = key.encode('utf8')
    if (key in cookies):
        del cookies[key]
        del self.headers['Set-Cookie']
        for m in cookies.values():
            self.headerlist.append(('Set-Cookie', m.serialize()))
    elif strict:
        raise KeyError(('No    cookie    has    been    set    with    the    name    %r' % key))
