piker/piker/_async_utils.py

# piker: trading gear for hackers
# Copyright (C) 2018-present  Tyler Goodlet (in stewardship of piker0)

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.

# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

"""
Async utils no one seems to have built into a core lib (yet).
"""
from typing import AsyncContextManager
from collections import OrderedDict
from contextlib import asynccontextmanager


def async_lifo_cache(maxsize=128):
    """Async ``cache`` with a LIFO policy.

    Implemented my own since no one else seems to have
    a standard. I'll wait for the smarter people to come
    up with one, but until then...
    """
    cache = OrderedDict()

    def decorator(fn):

        async def wrapper(*args):
            key = args
            try:
                return cache[key]
            except KeyError:
                if len(cache) >= maxsize:
                    # discard last added new entry
                    cache.popitem()

                # do it
                cache[key] = await fn(*args)
                return cache[key]

        return wrapper

    return decorator


@asynccontextmanager
async def _just_none():
    # noop -> skip entering context
    yield None


@asynccontextmanager
async def maybe_with_if(
    predicate: bool,
    context: AsyncContextManager,
) -> AsyncContextManager:
    async with context if predicate else _just_none() as output:
        yield output