cached_property.py

__author__ = "Daniel Roy Greenfeld"
__email__ = "daniel@feldroy.com"
__version__ = "2.0.1"
__license__ = "BSD"

from functools import wraps
from time import time
import threading
import asyncio


class cached_property:
    """
    A property that is only computed once per instance and then replaces itself
    with an ordinary attribute. Deleting the attribute resets the property.
    Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76
    """  # noqa

    def __init__(self, func):
        self.__doc__ = getattr(func, "__doc__")
        self.func = func

    def __get__(self, obj, cls):
        if obj is None:
            return self

        if asyncio.iscoroutinefunction(self.func):
            return self._wrap_in_coroutine(obj)

        value = obj.__dict__[self.func.__name__] = self.func(obj)
        return value

    def _wrap_in_coroutine(self, obj):
        @wraps(obj)
        def wrapper():
            future = asyncio.ensure_future(self.func(obj))
            obj.__dict__[self.func.__name__] = future
            return future

        return wrapper()


class threaded_cached_property:
    """
    A cached_property version for use in environments where multiple threads
    might concurrently try to access the property.
    """

    def __init__(self, func):
        self.__doc__ = getattr(func, "__doc__")
        self.func = func
        self.lock = threading.RLock()

    def __get__(self, obj, cls):
        if obj is None:
            return self

        obj_dict = obj.__dict__
        name = self.func.__name__
        with self.lock:
            try:
                # check if the value was computed before the lock was acquired
                return obj_dict[name]

            except KeyError:
                # if not, do the calculation and release the lock
                return obj_dict.setdefault(name, self.func(obj))


class cached_property_with_ttl:
    """
    A property that is only computed once per instance and then replaces itself
    with an ordinary attribute. Setting the ttl to a number expresses how long
    the property will last before being timed out.
    """

    def __init__(self, ttl=None):
        if callable(ttl):
            func = ttl
            ttl = None
        else:
            func = None
        self.ttl = ttl
        self._prepare_func(func)

    def __call__(self, func):
        self._prepare_func(func)
        return self

    def __get__(self, obj, cls):
        if obj is None:
            return self

        now = time()
        obj_dict = obj.__dict__
        name = self.__name__
        try:
            value, last_updated = obj_dict[name]
        except KeyError:
            pass
        else:
            ttl_expired = self.ttl and self.ttl < now - last_updated
            if not ttl_expired:
                return value

        value = self.func(obj)
        obj_dict[name] = (value, now)
        return value

    def __delete__(self, obj):
        obj.__dict__.pop(self.__name__, None)

    def __set__(self, obj, value):
        obj.__dict__[self.__name__] = (value, time())

    def _prepare_func(self, func):
        self.func = func
        if func:
            self.__doc__ = func.__doc__
            self.__name__ = func.__name__
            self.__module__ = func.__module__


# Aliases to make cached_property_with_ttl easier to use
cached_property_ttl = cached_property_with_ttl
timed_cached_property = cached_property_with_ttl


class threaded_cached_property_with_ttl(cached_property_with_ttl):
    """
    A cached_property version for use in environments where multiple threads
    might concurrently try to access the property.
    """

    def __init__(self, ttl=None):
        super(threaded_cached_property_with_ttl, self).__init__(ttl)
        self.lock = threading.RLock()

    def __get__(self, obj, cls):
        with self.lock:
            return super(threaded_cached_property_with_ttl, self).__get__(obj, cls)


# Alias to make threaded_cached_property_with_ttl easier to use
threaded_cached_property_ttl = threaded_cached_property_with_ttl
timed_threaded_cached_property = threaded_cached_property_with_ttl