bpo-42455: Add decorator_factory to functools module

[uriyyo]

Add decorator_factory to functools module.

More information regarding this feature: https://bugs.python.org/issue42455#msg381773

I have just gone through the standard library code to find places where decorator_factory can be used.

1. dataclasses.dataclass

def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
              unsafe_hash=False, frozen=False):
    """Returns the same class as was passed in, with dunder methods
    added based on the fields defined in the class.

    Examines PEP 526 __annotations__ to determine fields.

    If init is true, an __init__() method is added to the class. If
    repr is true, a __repr__() method is added. If order is true, rich
    comparison dunder methods are added. If unsafe_hash is true, a
    __hash__() method function is added. If frozen is true, fields may
    not be assigned to after instance creation.
    """

    def wrap(cls):
        return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)

    # See if we're being called as @dataclass or @dataclass().
    if cls is None:
        # We're called with parens.
        return wrap

    # We're called as @dataclass without parens.
    return wrap(cls)

@functools.decorator_factory
def dataclass(cls, /, *, init=True, repr=True, eq=True, order=False,
              unsafe_hash=False, frozen=False):
    """Returns the same class as was passed in, with dunder methods
    added based on the fields defined in the class.

    Examines PEP 526 __annotations__ to determine fields.

    If init is true, an __init__() method is added to the class. If
    repr is true, a __repr__() method is added. If order is true, rich
    comparison dunder methods are added. If unsafe_hash is true, a
    __hash__() method function is added. If frozen is true, fields may
    not be assigned to after instance creation.
    """
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)

2. functools.lru_cache

def lru_cache(maxsize=128, typed=False):
    """Least-recently-used cache decorator.

    If *maxsize* is set to None, the LRU features are disabled and the cache
    can grow without bound.

    If *typed* is True, arguments of different types will be cached separately.
    For example, f(3.0) and f(3) will be treated as distinct calls with
    distinct results.

    Arguments to the cached function must be hashable.

    View the cache statistics named tuple (hits, misses, maxsize, currsize)
    with f.cache_info().  Clear the cache and statistics with f.cache_clear().
    Access the underlying function with f.__wrapped__.

    See:  http://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)

    """

    # Users should only access the lru_cache through its public API:
    #       cache_info, cache_clear, and f.__wrapped__
    # The internals of the lru_cache are encapsulated for thread safety and
    # to allow the implementation to change (including a possible C version).

    if isinstance(maxsize, int):
        # Negative maxsize is treated as 0
        if maxsize < 0:
            maxsize = 0
    elif callable(maxsize) and isinstance(typed, bool):
        # The user_function was passed in directly via the maxsize argument
        user_function, maxsize = maxsize, 128
        wrapper = _lru_cache_wrapper(user_function, maxsize, typed, _CacheInfo)
        wrapper.cache_parameters = lambda : {'maxsize': maxsize, 'typed': typed}
        return update_wrapper(wrapper, user_function)
    elif maxsize is not None:
        raise TypeError(
            'Expected first argument to be an integer, a callable, or None')

    def decorating_function(user_function):
        wrapper = _lru_cache_wrapper(user_function, maxsize, typed, _CacheInfo)
        wrapper.cache_parameters = lambda : {'maxsize': maxsize, 'typed': typed}
        return update_wrapper(wrapper, user_function)

    return decorating_function

@decorator_factory
def lru_cache(user_function, /, maxsize=128, typed=False):
    """Least-recently-used cache decorator.

    If *maxsize* is set to None, the LRU features are disabled and the cache
    can grow without bound.

    If *typed* is True, arguments of different types will be cached separately.
    For example, f(3.0) and f(3) will be treated as distinct calls with
    distinct results.

    Arguments to the cached function must be hashable.

    View the cache statistics named tuple (hits, misses, maxsize, currsize)
    with f.cache_info().  Clear the cache and statistics with f.cache_clear().
    Access the underlying function with f.__wrapped__.

    See:  http://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)

    """

    # Users should only access the lru_cache through its public API:
    #       cache_info, cache_clear, and f.__wrapped__
    # The internals of the lru_cache are encapsulated for thread safety and
    # to allow the implementation to change (including a possible C version).

    if isinstance(maxsize, int):
        # Negative maxsize is treated as 0
        if maxsize < 0:
            maxsize = 0
    elif maxsize is not None:
        raise TypeError(
            'Expected first argument to be an integer, a callable, or None')

    wrapper = _lru_cache_wrapper(user_function, maxsize, typed, _CacheInfo)
    wrapper.cache_parameters = lambda : {'maxsize': maxsize, 'typed': typed}
    return update_wrapper(wrapper, user_function)

3. reprlib.recursive_repr

def recursive_repr(fillvalue='...'):
    'Decorator to make a repr function return fillvalue for a recursive call'

    def decorating_function(user_function):
        repr_running = set()

        def wrapper(self):
            key = id(self), get_ident()
            if key in repr_running:
                return fillvalue
            repr_running.add(key)
            try:
                result = user_function(self)
            finally:
                repr_running.discard(key)
            return result

        # Can't use functools.wraps() here because of bootstrap issues
        wrapper.__module__ = getattr(user_function, '__module__')
        wrapper.__doc__ = getattr(user_function, '__doc__')
        wrapper.__name__ = getattr(user_function, '__name__')
        wrapper.__qualname__ = getattr(user_function, '__qualname__')
        wrapper.__annotations__ = getattr(user_function, '__annotations__', {})
        return wrapper

    return decorating_function

@decorator_factory
def recursive_repr(user_function, fillvalue='...'):
    'Decorator to make a repr function return fillvalue for a recursive call'
    repr_running = set()

    def wrapper(self):
        key = id(self), get_ident()
        if key in repr_running:
            return fillvalue
        repr_running.add(key)
        try:
            result = user_function(self)
        finally:
            repr_running.discard(key)
        return result

    # Can't use functools.wraps() here because of bootstrap issues
    wrapper.__module__ = getattr(user_function, '__module__')
    wrapper.__doc__ = getattr(user_function, '__doc__')
    wrapper.__name__ = getattr(user_function, '__name__')
    wrapper.__qualname__ = getattr(user_function, '__qualname__')
    wrapper.__annotations__ = getattr(user_function, '__annotations__', {})
    return wrapper

4. typing._tp_cache

def _tp_cache(func=None, /, *, typed=False):
    """Internal wrapper caching __getitem__ of generic types with a fallback to
    original function for non-hashable arguments.
    """
    def decorator(func):
        cached = functools.lru_cache(typed=typed)(func)
        _cleanups.append(cached.cache_clear)

        @functools.wraps(func)
        def inner(*args, **kwds):
            try:
                return cached(*args, **kwds)
            except TypeError:
                pass  # All real errors (not unhashable args) are raised below.
            return func(*args, **kwds)
        return inner

    if func is not None:
        return decorator(func)

    return decorator

@functools.decorator_factory
def _tp_cache(func, /, *, typed=False):
    """Internal wrapper caching __getitem__ of generic types with a fallback to
    original function for non-hashable arguments.
    """
    cached = functools.lru_cache(typed=typed)(func)
    _cleanups.append(cached.cache_clear)

    @functools.wraps(func)
    def inner(*args, **kwds):
        try:
            return cached(*args, **kwds)
        except TypeError:
            pass  # All real errors (not unhashable args) are raised below.
        return func(*args, **kwds)

    return inner

https://bugs.python.org/issue42455

[uriyyo]

@serhiy-storchaka Can you please review this PR?

[rhettinger]

Please add a documentation update as well.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.