__contains__ fails for Cookies instance with a duplicate key

[alex-postolache]

Hey there,

I've encountered the following issue: name in cookies will fail with a CookieConflict when a Cookie instance contains multiple cookies with the same name (but different domains/paths). Code to reproduce:

import httpx
cookies = httpx.Cookies()
cookies.set("name", "value")
cookies.set("name", "value2", domain="example.com")
"name" in cookies

I've tracked the issue to the fact that Cookies does not implement __contains__, but it defers to its parent Mapping.__contains__. This in turn will trigger a call to Cookies.get(name) and hit the following code path:

def get(  # type: ignore
    self,
    name: str,
    ...
) -> typing.Optional[str]:
    ...
    value = None
    for cookie in self.jar:
        if cookie.name == name:
            if domain is None or cookie.domain == domain:
                if path is None or cookie.path == path:
                    if value is not None:
                        message = f"Multiple cookies exist with name={name}"
                        raise CookieConflict(message)
                    value = cookie.value
    ...

My hunch is that we should get a True instead since such a cookie exists in the jar.

Do you think it's correct to have a __contains__ defined on Cookie, like the one below?

class Cookie:
    def __contains__(self, name: str) -> bool:
        try:
            return self.get(name) is not None
        except CookieConflict:
            return True