This tracker is for modifying the cpython distribution -- the interpreter, stdlib, doc, and other associated files.  Questions about using cpython and 3rd party libraries like aiohttp should be directed elsewhere.

So, the relevant question here is whether http.cookies has a bug.  I reproduced the reported behavior in 3.7.0b1.

>>> from http.cookies import SimpleCookie
>>> sc = SimpleCookie()
>>> sc.load('LOGIN_SESSION=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; path=/; domain=.etoday.co.kr')
>>> sc
<SimpleCookie: LOGIN_SESSION='deleted'>
>>> sc.keys()
dict_keys(['LOGIN_SESSION'])
>>> sc['LOGIN_SESSION']
<Morsel: LOGIN_SESSION=deleted; Domain=.etoday.co.kr; expires=Thu, 01-Jan-1970 00:00:01 GMT; Path=/>
>>> sc.load('LOGIN_SESSION=18676-0.53621000; path=/; domain=.etoday.co.kr')
>>> sc['LOGIN_SESSION']
<Morsel: LOGIN_SESSION=18676-0.53621000; Domain=.etoday.co.kr; expires=Thu, 01-Jan-1970 00:00:01 GMT; Path=/>

The Morsel created in the first call is used in the second call because _parse_string ends with

                assert tp == TYPE_KEYVALUE
                rval, cval = value
                self.__set(key, rval, cval)
                M = self[key]

and __set begins with

        M = self.get(key, Morsel())
        M.set(key, real_value, coded_value)
        dict.__setitem__(self, key, M)

Is this a bug?  I know little about cookies, but https://tools.ietf.org/html/rfc2109.html has 
"
4.3.3  Cookie Management

   If a user agent receives a Set-Cookie response header whose NAME is
   the same as a pre-existing cookie, and whose Domain and Path
   attribute values exactly (string) match those of a pre-existing
   cookie, the new cookie supersedes the old. ..."

I don't know if pre-existing means 'previous session', 'previous server response', or 'previous header'.  I have no idea if duplicate cookies in the same response is even legal.  Even if it is, the server would do better to not do so or explicitly give a new expires date.  And if we do 
make a change, we might limit it to future versions.

David, what do you think?  Close as 'not a bug' or 'fix'?