__init__.py

"""Extensible memoizing collections and decorators."""

__all__ = (
    "Cache",
    "FIFOCache",
    "LFUCache",
    "LRUCache",
    "MRUCache",
    "RRCache",
    "TTLCache",
    "cached",
    "cachedmethod",
)

__version__ = "4.2.2"

import collections
import collections.abc
import functools
import random
import time

from .keys import hashkey


class _DefaultSize:

    __slots__ = ()

    def __getitem__(self, _):
        return 1

    def __setitem__(self, _, value):
        assert value == 1

    def pop(self, _):
        return 1


class Cache(collections.abc.MutableMapping):
    """Mutable mapping to serve as a simple cache or cache base class."""

    __marker = object()

    __size = _DefaultSize()

    def __init__(self, maxsize, getsizeof=None):
        if getsizeof:
            self.getsizeof = getsizeof
        if self.getsizeof is not Cache.getsizeof:
            self.__size = dict()
        self.__data = dict()
        self.__currsize = 0
        self.__maxsize = maxsize

    def __repr__(self):
        return "%s(%r, maxsize=%r, currsize=%r)" % (
            self.__class__.__name__,
            list(self.__data.items()),
            self.__maxsize,
            self.__currsize,
        )

    def __getitem__(self, key):
        try:
            return self.__data[key]
        except KeyError:
            return self.__missing__(key)

    def __setitem__(self, key, value):
        maxsize = self.__maxsize
        size = self.getsizeof(value)
        if size > maxsize:
            raise ValueError("value too large")
        if key not in self.__data or self.__size[key] < size:
            while self.__currsize + size > maxsize:
                self.popitem()
        if key in self.__data:
            diffsize = size - self.__size[key]
        else:
            diffsize = size
        self.__data[key] = value
        self.__size[key] = size
        self.__currsize += diffsize

    def __delitem__(self, key):
        size = self.__size.pop(key)
        del self.__data[key]
        self.__currsize -= size

    def __contains__(self, key):
        return key in self.__data

    def __missing__(self, key):
        raise KeyError(key)

    def __iter__(self):
        return iter(self.__data)

    def __len__(self):
        return len(self.__data)

    def get(self, key, default=None):
        if key in self:
            return self[key]
        else:
            return default

    def pop(self, key, default=__marker):
        if key in self:
            value = self[key]
            del self[key]
        elif default is self.__marker:
            raise KeyError(key)
        else:
            value = default
        return value

    def setdefault(self, key, default=None):
        if key in self:
            value = self[key]
        else:
            self[key] = value = default
        return value

    @property
    def maxsize(self):
        """The maximum size of the cache."""
        return self.__maxsize

    @property
    def currsize(self):
        """The current size of the cache."""
        return self.__currsize

    @staticmethod
    def getsizeof(value):
        """Return the size of a cache element's value."""
        return 1


class FIFOCache(Cache):
    """First In First Out (FIFO) cache implementation."""

    def __init__(self, maxsize, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__order = collections.OrderedDict()

    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
        cache_setitem(self, key, value)
        try:
            self.__order.move_to_end(key)
        except KeyError:
            self.__order[key] = None

    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
        cache_delitem(self, key)
        del self.__order[key]

    def popitem(self):
        """Remove and return the `(key, value)` pair first inserted."""
        try:
            key = next(iter(self.__order))
        except StopIteration:
            raise KeyError("%s is empty" % type(self).__name__) from None
        else:
            return (key, self.pop(key))


class LFUCache(Cache):
    """Least Frequently Used (LFU) cache implementation."""

    def __init__(self, maxsize, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__counter = collections.Counter()

    def __getitem__(self, key, cache_getitem=Cache.__getitem__):
        value = cache_getitem(self, key)
        if key in self:  # __missing__ may not store item
            self.__counter[key] -= 1
        return value

    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
        cache_setitem(self, key, value)
        self.__counter[key] -= 1

    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
        cache_delitem(self, key)
        del self.__counter[key]

    def popitem(self):
        """Remove and return the `(key, value)` pair least frequently used."""
        try:
            ((key, _),) = self.__counter.most_common(1)
        except ValueError:
            raise KeyError("%s is empty" % type(self).__name__) from None
        else:
            return (key, self.pop(key))


class LRUCache(Cache):
    """Least Recently Used (LRU) cache implementation."""

    def __init__(self, maxsize, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__order = collections.OrderedDict()

    def __getitem__(self, key, cache_getitem=Cache.__getitem__):
        value = cache_getitem(self, key)
        if key in self:  # __missing__ may not store item
            self.__update(key)
        return value

    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
        cache_setitem(self, key, value)
        self.__update(key)

    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
        cache_delitem(self, key)
        del self.__order[key]

    def popitem(self):
        """Remove and return the `(key, value)` pair least recently used."""
        try:
            key = next(iter(self.__order))
        except StopIteration:
            raise KeyError("%s is empty" % type(self).__name__) from None
        else:
            return (key, self.pop(key))

    def __update(self, key):
        try:
            self.__order.move_to_end(key)
        except KeyError:
            self.__order[key] = None


class MRUCache(Cache):
    """Most Recently Used (MRU) cache implementation."""

    def __init__(self, maxsize, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__order = collections.OrderedDict()

    def __getitem__(self, key, cache_getitem=Cache.__getitem__):
        value = cache_getitem(self, key)
        if key in self:  # __missing__ may not store item
            self.__update(key)
        return value

    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
        cache_setitem(self, key, value)
        self.__update(key)

    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
        cache_delitem(self, key)
        del self.__order[key]

    def popitem(self):
        """Remove and return the `(key, value)` pair most recently used."""
        try:
            key = next(iter(self.__order))
        except StopIteration:
            raise KeyError("%s is empty" % type(self).__name__) from None
        else:
            return (key, self.pop(key))

    def __update(self, key):
        try:
            self.__order.move_to_end(key, last=False)
        except KeyError:
            self.__order[key] = None


class RRCache(Cache):
    """Random Replacement (RR) cache implementation."""

    def __init__(self, maxsize, choice=random.choice, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__choice = choice

    @property
    def choice(self):
        """The `choice` function used by the cache."""
        return self.__choice

    def popitem(self):
        """Remove and return a random `(key, value)` pair."""
        try:
            key = self.__choice(list(self))
        except IndexError:
            raise KeyError("%s is empty" % type(self).__name__) from None
        else:
            return (key, self.pop(key))


class _Timer:
    def __init__(self, timer):
        self.__timer = timer
        self.__nesting = 0

    def __call__(self):
        if self.__nesting == 0:
            return self.__timer()
        else:
            return self.__time

    def __enter__(self):
        if self.__nesting == 0:
            self.__time = time = self.__timer()
        else:
            time = self.__time
        self.__nesting += 1
        return time

    def __exit__(self, *exc):
        self.__nesting -= 1

    def __reduce__(self):
        return _Timer, (self.__timer,)

    def __getattr__(self, name):
        return getattr(self.__timer, name)


class _Link:

    __slots__ = ("key", "expire", "next", "prev")

    def __init__(self, key=None, expire=None):
        self.key = key
        self.expire = expire

    def __reduce__(self):
        return _Link, (self.key, self.expire)

    def unlink(self):
        next = self.next
        prev = self.prev
        prev.next = next
        next.prev = prev


class TTLCache(Cache):
    """LRU Cache implementation with per-item time-to-live (TTL) value."""

    def __init__(self, maxsize, ttl, timer=time.monotonic, getsizeof=None):
        Cache.__init__(self, maxsize, getsizeof)
        self.__root = root = _Link()
        root.prev = root.next = root
        self.__links = collections.OrderedDict()
        self.__timer = _Timer(timer)
        self.__ttl = ttl

    def __contains__(self, key):
        try:
            link = self.__links[key]  # no reordering
        except KeyError:
            return False
        else:
            return not (link.expire < self.__timer())

    def __getitem__(self, key, cache_getitem=Cache.__getitem__):
        try:
            link = self.__getlink(key)
        except KeyError:
            expired = False
        else:
            expired = link.expire < self.__timer()
        if expired:
            return self.__missing__(key)
        else:
            return cache_getitem(self, key)

    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
        with self.__timer as time:
            self.expire(time)
            cache_setitem(self, key, value)
        try:
            link = self.__getlink(key)
        except KeyError:
            self.__links[key] = link = _Link(key)
        else:
            link.unlink()
        link.expire = time + self.__ttl
        link.next = root = self.__root
        link.prev = prev = root.prev
        prev.next = root.prev = link

    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
        cache_delitem(self, key)
        link = self.__links.pop(key)
        link.unlink()
        if link.expire < self.__timer():
            raise KeyError(key)

    def __iter__(self):
        root = self.__root
        curr = root.next
        while curr is not root:
            # "freeze" time for iterator access
            with self.__timer as time:
                if not (curr.expire < time):
                    yield curr.key
            curr = curr.next

    def __len__(self):
        root = self.__root
        curr = root.next
        time = self.__timer()
        count = len(self.__links)
        while curr is not root and curr.expire < time:
            count -= 1
            curr = curr.next
        return count

    def __setstate__(self, state):
        self.__dict__.update(state)
        root = self.__root
        root.prev = root.next = root
        for link in sorted(self.__links.values(), key=lambda obj: obj.expire):
            link.next = root
            link.prev = prev = root.prev
            prev.next = root.prev = link
        self.expire(self.__timer())

    def __repr__(self, cache_repr=Cache.__repr__):
        with self.__timer as time:
            self.expire(time)
            return cache_repr(self)

    @property
    def currsize(self):
        with self.__timer as time:
            self.expire(time)
            return super().currsize

    @property
    def timer(self):
        """The timer function used by the cache."""
        return self.__timer

    @property
    def ttl(self):
        """The time-to-live value of the cache's items."""
        return self.__ttl

    def expire(self, time=None):
        """Remove expired items from the cache."""
        if time is None:
            time = self.__timer()
        root = self.__root
        curr = root.next
        links = self.__links
        cache_delitem = Cache.__delitem__
        while curr is not root and curr.expire < time:
            cache_delitem(self, curr.key)
            del links[curr.key]
            next = curr.next
            curr.unlink()
            curr = next

    def clear(self):
        with self.__timer as time:
            self.expire(time)
            Cache.clear(self)

    def get(self, *args, **kwargs):
        with self.__timer:
            return Cache.get(self, *args, **kwargs)

    def pop(self, *args, **kwargs):
        with self.__timer:
            return Cache.pop(self, *args, **kwargs)

    def setdefault(self, *args, **kwargs):
        with self.__timer:
            return Cache.setdefault(self, *args, **kwargs)

    def popitem(self):
        """Remove and return the `(key, value)` pair least recently used that
        has not already expired.

        """
        with self.__timer as time:
            self.expire(time)
            try:
                key = next(iter(self.__links))
            except StopIteration:
                raise KeyError("%s is empty" % type(self).__name__) from None
            else:
                return (key, self.pop(key))

    def __getlink(self, key):
        value = self.__links[key]
        self.__links.move_to_end(key)
        return value


def cached(cache, key=hashkey, lock=None):
    """Decorator to wrap a function with a memoizing callable that saves
    results in a cache.

    """

    def decorator(func):
        if cache is None:

            def wrapper(*args, **kwargs):
                return func(*args, **kwargs)

        elif lock is None:

            def wrapper(*args, **kwargs):
                k = key(*args, **kwargs)
                try:
                    return cache[k]
                except KeyError:
                    pass  # key not found
                v = func(*args, **kwargs)
                try:
                    cache[k] = v
                except ValueError:
                    pass  # value too large
                return v

        else:

            def wrapper(*args, **kwargs):
                k = key(*args, **kwargs)
                try:
                    with lock:
                        return cache[k]
                except KeyError:
                    pass  # key not found
                v = func(*args, **kwargs)
                # in case of a race, prefer the item already in the cache
                try:
                    with lock:
                        return cache.setdefault(k, v)
                except ValueError:
                    return v  # value too large

        return functools.update_wrapper(wrapper, func)

    return decorator


def cachedmethod(cache, key=hashkey, lock=None):
    """Decorator to wrap a class or instance method with a memoizing
    callable that saves results in a cache.

    """

    def decorator(method):
        if lock is None:

            def wrapper(self, *args, **kwargs):
                c = cache(self)
                if c is None:
                    return method(self, *args, **kwargs)
                k = key(*args, **kwargs)
                try:
                    return c[k]
                except KeyError:
                    pass  # key not found
                v = method(self, *args, **kwargs)
                try:
                    c[k] = v
                except ValueError:
                    pass  # value too large
                return v

        else:

            def wrapper(self, *args, **kwargs):
                c = cache(self)
                if c is None:
                    return method(self, *args, **kwargs)
                k = key(*args, **kwargs)
                try:
                    with lock(self):
                        return c[k]
                except KeyError:
                    pass  # key not found
                v = method(self, *args, **kwargs)
                # in case of a race, prefer the item already in the cache
                try:
                    with lock(self):
                        return c.setdefault(k, v)
                except ValueError:
                    return v  # value too large

        return functools.update_wrapper(wrapper, method)

    return decorator