superset/utils/memoized.py

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# to you under the Apache License, Version 2.0 (the
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#
#   http://www.apache.org/licenses/LICENSE-2.0
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# under the License.
import functools
from typing import Any, Callable, Dict, Optional, Tuple, Type


class _memoized:
    """Decorator that caches a function's return value each time it is called

    If called later with the same arguments, the cached value is returned, and
    not re-evaluated.

    Define ``watch`` as a tuple of attribute names if this Decorator
    should account for instance variable changes.
    """

    def __init__(
        self, func: Callable[..., Any], watch: Optional[Tuple[str, ...]] = None
    ) -> None:
        self.func = func
        self.cache: Dict[Any, Any] = {}
        self.is_method = False
        self.watch = watch or ()

    def __call__(self, *args: Any, **kwargs: Any) -> Any:
        key = [args, frozenset(kwargs.items())]
        if self.is_method:
            key.append(tuple(getattr(args[0], v, None) for v in self.watch))
        key = tuple(key)  # type: ignore
        try:
            if key in self.cache:
                return self.cache[key]
        except TypeError as ex:
            # Uncachable -- for instance, passing a list as an argument.
            raise TypeError("Function cannot be memoized") from ex
        value = self.func(*args, **kwargs)
        try:
            self.cache[key] = value
        except TypeError as ex:
            raise TypeError("Function cannot be memoized") from ex
        return value

    def __repr__(self) -> str:
        """Return the function's docstring."""
        return self.func.__doc__ or ""

    def __get__(
        self, obj: Any, objtype: Type[Any]
    ) -> functools.partial:  # type: ignore
        if not self.is_method:
            self.is_method = True
        # Support instance methods.
        return functools.partial(self.__call__, obj)


def memoized(
    func: Optional[Callable[..., Any]] = None, watch: Optional[Tuple[str, ...]] = None
) -> Callable[..., Any]:
    if func:
        return _memoized(func)

    def wrapper(f: Callable[..., Any]) -> Callable[..., Any]:
        return _memoized(f, watch)

    return wrapper