#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright (c) 2020 Satpy developers
#
# This file is part of satpy.
#
# satpy is free software: you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.
#
# satpy 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# satpy. If not, see <http://www.gnu.org/licenses/>.
"""Backports and compatibility fixes for satpy."""
from threading import RLock
_NOT_FOUND = object()
[docs]
class CachedPropertyBackport:
"""Backport of cached_property from Python-3.8.
Source: https://github.com/python/cpython/blob/v3.8.0/Lib/functools.py#L930
"""
def __init__(self, func): # noqa
self.func = func
self.attrname = None
self.__doc__ = func.__doc__
self.lock = RLock()
def __set_name__(self, owner, name): # noqa
if self.attrname is None:
self.attrname = name
elif name != self.attrname:
raise TypeError(
"Cannot assign the same cached_property to two different names "
f"({self.attrname!r} and {name!r})."
)
def __get__(self, instance, owner=None): # noqa
if instance is None:
return self
if self.attrname is None:
raise TypeError(
"Cannot use cached_property instance without calling __set_name__ on it.")
try:
cache = instance.__dict__ # noqa
except AttributeError: # not all objects have __dict__ (e.g. class defines slots)
msg = (
f"No '__dict__' attribute on {type(instance).__name__!r} "
f"instance to cache {self.attrname!r} property."
)
raise TypeError(msg) from None
val = cache.get(self.attrname, _NOT_FOUND)
if val is _NOT_FOUND:
with self.lock:
# check if another thread filled cache while we awaited lock
val = cache.get(self.attrname, _NOT_FOUND)
if val is _NOT_FOUND:
val = self.func(instance)
try:
cache[self.attrname] = val
except TypeError:
msg = (
f"The '__dict__' attribute on {type(instance).__name__!r} instance "
f"does not support item assignment for caching {self.attrname!r} property."
)
raise TypeError(msg) from None
return val
try:
from functools import cached_property # type: ignore
except ImportError:
# for python < 3.8
cached_property = CachedPropertyBackport # type: ignore
try:
from numpy.typing import ArrayLike, DTypeLike # noqa
except ImportError:
# numpy <1.20
from numpy import dtype as DTypeLike # noqa
from numpy import ndarray as ArrayLike # noqa
try:
from functools import cache # type: ignore
except ImportError:
from functools import lru_cache as cache # noqa