Morsel.__init__ loops reserved values and could be replaced with a simple dict update

[bdraco]

cpython/Lib/http/cookies.py

Line 276 in 224c370

for key in self._reserved:

Backstory:
aio-libs/aiohttp#9594
Processing cookies is a significant part of the aiohttp request time, and some requesters have to create many Morsel objects because they have a lot of cookies on every request.

There are few places that can be optimized in http.cookies

This one is low hanging fruit

Linked PRs

• gh-126156: Improve performance of creating Morsel objects #126157

[bdraco]

(venv) bdraco cpython % python3 morsel_bench.py
0.33160758309531957 - original
0.28600058297161013 - new
(venv) bdraco cpython % cat morsel_bench.py

from http.cookies import Morsel
import timeit


class FastMorsel(dict):
    """A class to hold ONE (key, value) pair.

    In a cookie, each such pair may have several attributes, so this class is
    used to keep the attributes associated with the appropriate key,value pair.
    This class also includes a coded_value attribute, which is used to hold
    the network representation of the value.
    """

    # RFC 2109 lists these attributes as reserved:
    #   path       comment         domain
    #   max-age    secure      version
    #
    # For historical reasons, these attributes are also reserved:
    #   expires
    #
    # This is an extension from Microsoft:
    #   httponly
    #
    # This dictionary provides a mapping from the lowercase
    # variant on the left to the appropriate traditional
    # formatting on the right.
    _reserved = {
        "expires": "expires",
        "path": "Path",
        "comment": "Comment",
        "domain": "Domain",
        "max-age": "Max-Age",
        "secure": "Secure",
        "httponly": "HttpOnly",
        "version": "Version",
        "samesite": "SameSite",
    }

    _reserved_defaults = {key: "" for key in _reserved}

    _flags = {"secure", "httponly"}

    def __init__(self):
        # Set defaults
        self._key = self._value = self._coded_value = None

        # Set default attributes
        dict.update(self, self._reserved_defaults)


print(timeit.timeit("Morsel()", globals={"Morsel": Morsel}))
print(timeit.timeit("FastMorsel()", globals={"FastMorsel": FastMorsel}))