Futures

pykka.Future

Bases: Generic[T]

A handle to a value which is available now or in the future.

Typically returned by calls to actor methods or accesses to actor fields.

To get hold of the encapsulated value, call Future.get() or await the future.

Source code in src/pykka/_future.py

class Future(Generic[T]):
    """A handle to a value which is available now or in the future.

    Typically returned by calls to actor methods or accesses to actor fields.

    To get hold of the encapsulated value, call
    [`Future.get()`][pykka.Future.get] or `await` the future.
    """

    _get_hook: GetHookFunc[T] | None
    _get_hook_result: T | _Unset

    def __init__(self) -> None:
        super().__init__()
        self._get_hook = None
        self._get_hook_result = _Unset()

    def __repr__(self) -> str:
        return "<pykka.Future>"

    def get(
        self,
        *,
        timeout: float | None = None,
    ) -> T:
        """Get the value encapsulated by the future.

        If the encapsulated value is an exception, it is raised instead of
        returned.

        If `timeout` is `None`, as default, the method will block until it gets
        a reply, potentially forever. If `timeout` is an integer or float, the
        method will wait for a reply for `timeout` seconds, and then raise
        [`Timeout`][pykka.Timeout].

        The encapsulated value can be retrieved multiple times. The future will
        only block the first time the value is accessed.

        Args:
            timeout: seconds to wait before timeout

        Raises:
            pykka.Timeout: if timeout is reached
            Exception: encapsulated value if it is an exception

        Returns:
            encapsulated value if it is not an exception

        """
        if self._get_hook is not None:
            if isinstance(self._get_hook_result, _Unset):
                self._get_hook_result = self._get_hook(timeout)
            return self._get_hook_result
        raise NotImplementedError

    def set(
        self,
        value: T | None = None,
    ) -> None:
        """Set the encapsulated value.

        Args:
            value: the encapsulated value or nothing

        Raises:
            Exception: an exception if `set()` is called multiple times

        /// note | Version changed: Pykka 4.3
        Calling `set()` on a future that already has a get hook set now
        raises an exception.
        ///

        """
        raise NotImplementedError

    def set_exception(
        self,
        exc_info: OptExcInfo | None = None,
    ) -> None:
        """Set an exception as the encapsulated value.

        You can pass an `exc_info` three-tuple, as returned by
        [`sys.exc_info()`][sys.exc_info]. If you don't pass `exc_info`,
        [`sys.exc_info()`][sys.exc_info] will be called and the value returned
        by it used.

        In other words, if you're calling `set_exception()`, without any
        arguments, from an except block, the exception you're currently handling
        will automatically be set on the future.

        Args:
            exc_info: the encapsulated exception

        /// note | Version changed: Pykka 4.3
        Calling `set_exception()` on a future that already has a get hook
        set now raises an exception.
        ///

        """
        raise NotImplementedError

    def set_get_hook(
        self,
        func: GetHookFunc[T],
    ) -> None:
        """Set a function to be executed when [`get()`][pykka.Future.get] is called.

        The function will be called when [`get()`][pykka.Future.get] is called, with the
        `timeout` value as the only argument. The function's return value will
        be returned from [`get()`][pykka.Future.get].

        Args:
            func: callable accepting a timeout value, to produce return value of
                `get()`

        /// note | Version added: Pykka 1.2
        ///

        /// note | Version changed: Pykka 4.3
        Calling `set_get_hook()` on a future that already has a result set
        now raises an exception.
        ///

        """
        self._get_hook = func

    def filter(
        self: Future[Iterable[J]],
        func: Callable[[J], bool],
    ) -> Future[Iterable[J]]:
        """Return a new future with only the items passing the predicate function.

        If the future's value is an iterable, `filter()` will return a new
        future whose value is another iterable with only the items from the
        first iterable for which `func(item)` is true. If the future's value
        isn't an iterable, a [`TypeError`][TypeError] will be raised when
        [`get()`][pykka.Future.get] is called.

        Example:
            ```pycon
            >>> import pykka
            >>> f = pykka.ThreadingFuture()
            >>> g = f.filter(lambda x: x > 10)
            >>> g
            <pykka.future.ThreadingFuture at ...>
            >>> f.set(range(5, 15))
            >>> f.get()
            [5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
            >>> g.get()
            [11, 12, 13, 14]
            ```

        /// note | Version added: Pykka 1.2
        ///

        """
        future = self.__class__()
        future.set_get_hook(
            lambda timeout: list(filter(func, self.get(timeout=timeout)))
        )
        return future

    def join(
        self: Future[Any],
        *futures: Future[Any],
    ) -> Future[Iterable[Any]]:
        """Return a new future with a list of the result of multiple futures.

        One or more futures can be passed as arguments to `join()`. The new
        future returns a list with the results from all the joined futures.

        Example:
            ```pycon
            >>> import pykka
            >>> f1 = pykka.ThreadingFuture()
            >>> f2 = pykka.ThreadingFuture()
            >>> f3 = pykka.ThreadingFuture()
            >>> f = f1.join(f2, f3)
            >>> f1.set('abc')
            >>> f2.set(123)
            >>> f3.set(False)
            >>> f.get()
            ['abc', 123, False]
            ```

        /// note | Version added: Pykka 1.2
        ///

        """
        future = cast("Future[Iterable[Any]]", self.__class__())
        future.set_get_hook(
            lambda timeout: [f.get(timeout=timeout) for f in [self, *futures]]
        )
        return future

    def map(
        self,
        func: Callable[[T], M],
    ) -> Future[M]:
        """Pass the result of the future through a function.

        Example:
            ```pycon
            >>> import pykka

            >>> f = pykka.ThreadingFuture()
            >>> g = f.map(lambda x: x + 10)
            >>> f.set(30)
            >>> g.get()
            40

            >>> f = pykka.ThreadingFuture()
            >>> g = f.map(lambda x: x['foo'])
            >>> f.set({'foo': 'bar'}})
            >>> g.get()
            'bar'
            ```

        /// note | Version added: Pykka 1.2
        ///

        /// note | Version changed: Pykka 2.0
        Previously, if the future's result was an iterable (except a
        string), the function was applied to each item in the iterable.
        This behavior was unpredictable and made regular use cases like
        extracting a single field from a dict difficult, thus the
        behavior has been simplified. Since Pykka 2.0, the entire result
        value is passed to the function.
        ///

        """
        future = cast("Future[M]", self.__class__())
        future.set_get_hook(lambda timeout: func(self.get(timeout=timeout)))
        return future

    def reduce(
        self: Future[Iterable[J]],
        func: Callable[[R, J], R],
        *args: R,
    ) -> Future[R]:
        """Reduce a future's iterable result to a single value.

        The function of two arguments is applied cumulatively to the items of
        the iterable, from left to right. The result of the first function call
        is used as the first argument to the second function call, and so on,
        until the end of the iterable. If the future's value isn't an iterable,
        a [`TypeError`][TypeError] is raised.

        `reduce()` accepts an optional second argument, which will be used as an
        initial value in the first function call. If the iterable is empty, the
        initial value is returned.

        Example:
            ```pycon
            >>> import pykka

            >>> f = pykka.ThreadingFuture()
            >>> g = f.reduce(lambda x, y: x + y)
            >>> f.set(['a', 'b', 'c'])
            >>> g.get()
            'abc'

            >>> f = pykka.ThreadingFuture()
            >>> g = f.reduce(lambda x, y: x + y)
            >>> f.set([1, 2, 3])
            >>> (1 + 2) + 3
            6
            >>> g.get()
            6

            >>> f = pykka.ThreadingFuture()
            >>> g = f.reduce(lambda x, y: x + y, 5)
            >>> f.set([1, 2, 3])
            >>> ((5 + 1) + 2) + 3
            11
            >>> g.get()
            11

            >>> f = pykka.ThreadingFuture()
            >>> g = f.reduce(lambda x, y: x + y, 5)
            >>> f.set([])
            >>> g.get()
            5
            ```

        /// note | Version added: Pykka 1.2
        ///

        """
        future = cast("Future[R]", self.__class__())
        future.set_get_hook(
            lambda timeout: functools.reduce(func, self.get(timeout=timeout), *args)
        )
        return future

    def __await__(self) -> Generator[None, None, T]:
        yield
        value = self.get()
        return value

    __iter__ = __await__

filter

filter(func: Callable[[J], bool]) -> Future[Iterable[J]]

Return a new future with only the items passing the predicate function.

If the future's value is an iterable, filter() will return a new future whose value is another iterable with only the items from the first iterable for which func(item) is true. If the future's value isn't an iterable, a TypeError will be raised when get() is called.

Example

>>> import pykka
>>> f = pykka.ThreadingFuture()
>>> g = f.filter(lambda x: x > 10)
>>> g
<pykka.future.ThreadingFuture at ...>
>>> f.set(range(5, 15))
>>> f.get()
[5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
>>> g.get()
[11, 12, 13, 14]

Version added: Pykka 1.2

Source code in src/pykka/_future.py

def filter(
    self: Future[Iterable[J]],
    func: Callable[[J], bool],
) -> Future[Iterable[J]]:
    """Return a new future with only the items passing the predicate function.

    If the future's value is an iterable, `filter()` will return a new
    future whose value is another iterable with only the items from the
    first iterable for which `func(item)` is true. If the future's value
    isn't an iterable, a [`TypeError`][TypeError] will be raised when
    [`get()`][pykka.Future.get] is called.

    Example:
        ```pycon
        >>> import pykka
        >>> f = pykka.ThreadingFuture()
        >>> g = f.filter(lambda x: x > 10)
        >>> g
        <pykka.future.ThreadingFuture at ...>
        >>> f.set(range(5, 15))
        >>> f.get()
        [5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
        >>> g.get()
        [11, 12, 13, 14]
        ```

    /// note | Version added: Pykka 1.2
    ///

    """
    future = self.__class__()
    future.set_get_hook(
        lambda timeout: list(filter(func, self.get(timeout=timeout)))
    )
    return future

get

get(*, timeout: float | None = None) -> T

Get the value encapsulated by the future.

If the encapsulated value is an exception, it is raised instead of returned.

If timeout is None, as default, the method will block until it gets a reply, potentially forever. If timeout is an integer or float, the method will wait for a reply for timeout seconds, and then raise Timeout.

The encapsulated value can be retrieved multiple times. The future will only block the first time the value is accessed.

Parameters:

• timeout (float | None, default: None ) –

  seconds to wait before timeout

Raises:

• Timeout –

  if timeout is reached

• Exception –

  encapsulated value if it is an exception

Returns:

• T –

  encapsulated value if it is not an exception

Source code in src/pykka/_future.py

def get(
    self,
    *,
    timeout: float | None = None,
) -> T:
    """Get the value encapsulated by the future.

    If the encapsulated value is an exception, it is raised instead of
    returned.

    If `timeout` is `None`, as default, the method will block until it gets
    a reply, potentially forever. If `timeout` is an integer or float, the
    method will wait for a reply for `timeout` seconds, and then raise
    [`Timeout`][pykka.Timeout].

    The encapsulated value can be retrieved multiple times. The future will
    only block the first time the value is accessed.

    Args:
        timeout: seconds to wait before timeout

    Raises:
        pykka.Timeout: if timeout is reached
        Exception: encapsulated value if it is an exception

    Returns:
        encapsulated value if it is not an exception

    """
    if self._get_hook is not None:
        if isinstance(self._get_hook_result, _Unset):
            self._get_hook_result = self._get_hook(timeout)
        return self._get_hook_result
    raise NotImplementedError

join

join(*futures: Future[Any]) -> Future[Iterable[Any]]

Return a new future with a list of the result of multiple futures.

One or more futures can be passed as arguments to join(). The new future returns a list with the results from all the joined futures.

Example

>>> import pykka
>>> f1 = pykka.ThreadingFuture()
>>> f2 = pykka.ThreadingFuture()
>>> f3 = pykka.ThreadingFuture()
>>> f = f1.join(f2, f3)
>>> f1.set('abc')
>>> f2.set(123)
>>> f3.set(False)
>>> f.get()
['abc', 123, False]

Version added: Pykka 1.2

Source code in src/pykka/_future.py

def join(
    self: Future[Any],
    *futures: Future[Any],
) -> Future[Iterable[Any]]:
    """Return a new future with a list of the result of multiple futures.

    One or more futures can be passed as arguments to `join()`. The new
    future returns a list with the results from all the joined futures.

    Example:
        ```pycon
        >>> import pykka
        >>> f1 = pykka.ThreadingFuture()
        >>> f2 = pykka.ThreadingFuture()
        >>> f3 = pykka.ThreadingFuture()
        >>> f = f1.join(f2, f3)
        >>> f1.set('abc')
        >>> f2.set(123)
        >>> f3.set(False)
        >>> f.get()
        ['abc', 123, False]
        ```

    /// note | Version added: Pykka 1.2
    ///

    """
    future = cast("Future[Iterable[Any]]", self.__class__())
    future.set_get_hook(
        lambda timeout: [f.get(timeout=timeout) for f in [self, *futures]]
    )
    return future

map

map(func: Callable[[T], M]) -> Future[M]

Pass the result of the future through a function.

Example

>>> import pykka

>>> f = pykka.ThreadingFuture()
>>> g = f.map(lambda x: x + 10)
>>> f.set(30)
>>> g.get()
40

>>> f = pykka.ThreadingFuture()
>>> g = f.map(lambda x: x['foo'])
>>> f.set({'foo': 'bar'}})
>>> g.get()
'bar'

Version added: Pykka 1.2

Version changed: Pykka 2.0

Previously, if the future's result was an iterable (except a string), the function was applied to each item in the iterable. This behavior was unpredictable and made regular use cases like extracting a single field from a dict difficult, thus the behavior has been simplified. Since Pykka 2.0, the entire result value is passed to the function.

Source code in src/pykka/_future.py

def map(
    self,
    func: Callable[[T], M],
) -> Future[M]:
    """Pass the result of the future through a function.

    Example:
        ```pycon
        >>> import pykka

        >>> f = pykka.ThreadingFuture()
        >>> g = f.map(lambda x: x + 10)
        >>> f.set(30)
        >>> g.get()
        40

        >>> f = pykka.ThreadingFuture()
        >>> g = f.map(lambda x: x['foo'])
        >>> f.set({'foo': 'bar'}})
        >>> g.get()
        'bar'
        ```

    /// note | Version added: Pykka 1.2
    ///

    /// note | Version changed: Pykka 2.0
    Previously, if the future's result was an iterable (except a
    string), the function was applied to each item in the iterable.
    This behavior was unpredictable and made regular use cases like
    extracting a single field from a dict difficult, thus the
    behavior has been simplified. Since Pykka 2.0, the entire result
    value is passed to the function.
    ///

    """
    future = cast("Future[M]", self.__class__())
    future.set_get_hook(lambda timeout: func(self.get(timeout=timeout)))
    return future

reduce

reduce(func: Callable[[R, J], R], *args: R) -> Future[R]

Reduce a future's iterable result to a single value.

The function of two arguments is applied cumulatively to the items of the iterable, from left to right. The result of the first function call is used as the first argument to the second function call, and so on, until the end of the iterable. If the future's value isn't an iterable, a TypeError is raised.

reduce() accepts an optional second argument, which will be used as an initial value in the first function call. If the iterable is empty, the initial value is returned.

Example

>>> import pykka

>>> f = pykka.ThreadingFuture()
>>> g = f.reduce(lambda x, y: x + y)
>>> f.set(['a', 'b', 'c'])
>>> g.get()
'abc'

>>> f = pykka.ThreadingFuture()
>>> g = f.reduce(lambda x, y: x + y)
>>> f.set([1, 2, 3])
>>> (1 + 2) + 3
6
>>> g.get()
6

>>> f = pykka.ThreadingFuture()
>>> g = f.reduce(lambda x, y: x + y, 5)
>>> f.set([1, 2, 3])
>>> ((5 + 1) + 2) + 3
11
>>> g.get()
11

>>> f = pykka.ThreadingFuture()
>>> g = f.reduce(lambda x, y: x + y, 5)
>>> f.set([])
>>> g.get()
5

Version added: Pykka 1.2

Source code in src/pykka/_future.py

def reduce(
    self: Future[Iterable[J]],
    func: Callable[[R, J], R],
    *args: R,
) -> Future[R]:
    """Reduce a future's iterable result to a single value.

    The function of two arguments is applied cumulatively to the items of
    the iterable, from left to right. The result of the first function call
    is used as the first argument to the second function call, and so on,
    until the end of the iterable. If the future's value isn't an iterable,
    a [`TypeError`][TypeError] is raised.

    `reduce()` accepts an optional second argument, which will be used as an
    initial value in the first function call. If the iterable is empty, the
    initial value is returned.

    Example:
        ```pycon
        >>> import pykka

        >>> f = pykka.ThreadingFuture()
        >>> g = f.reduce(lambda x, y: x + y)
        >>> f.set(['a', 'b', 'c'])
        >>> g.get()
        'abc'

        >>> f = pykka.ThreadingFuture()
        >>> g = f.reduce(lambda x, y: x + y)
        >>> f.set([1, 2, 3])
        >>> (1 + 2) + 3
        6
        >>> g.get()
        6

        >>> f = pykka.ThreadingFuture()
        >>> g = f.reduce(lambda x, y: x + y, 5)
        >>> f.set([1, 2, 3])
        >>> ((5 + 1) + 2) + 3
        11
        >>> g.get()
        11

        >>> f = pykka.ThreadingFuture()
        >>> g = f.reduce(lambda x, y: x + y, 5)
        >>> f.set([])
        >>> g.get()
        5
        ```

    /// note | Version added: Pykka 1.2
    ///

    """
    future = cast("Future[R]", self.__class__())
    future.set_get_hook(
        lambda timeout: functools.reduce(func, self.get(timeout=timeout), *args)
    )
    return future

set

set(value: T | None = None) -> None

Set the encapsulated value.

Parameters:

• value (T | None, default: None ) –

  the encapsulated value or nothing

Raises:

• Exception –

  an exception if set() is called multiple times

Version changed: Pykka 4.3

Calling set() on a future that already has a get hook set now raises an exception.

Source code in src/pykka/_future.py

def set(
    self,
    value: T | None = None,
) -> None:
    """Set the encapsulated value.

    Args:
        value: the encapsulated value or nothing

    Raises:
        Exception: an exception if `set()` is called multiple times

    /// note | Version changed: Pykka 4.3
    Calling `set()` on a future that already has a get hook set now
    raises an exception.
    ///

    """
    raise NotImplementedError

set_exception

set_exception(exc_info: OptExcInfo | None = None) -> None

Set an exception as the encapsulated value.

You can pass an exc_info three-tuple, as returned by sys.exc_info(). If you don't pass exc_info, sys.exc_info() will be called and the value returned by it used.

In other words, if you're calling set_exception(), without any arguments, from an except block, the exception you're currently handling will automatically be set on the future.

Parameters:

• exc_info (OptExcInfo | None, default: None ) –

  the encapsulated exception

Version changed: Pykka 4.3

Calling set_exception() on a future that already has a get hook set now raises an exception.

Source code in src/pykka/_future.py

def set_exception(
    self,
    exc_info: OptExcInfo | None = None,
) -> None:
    """Set an exception as the encapsulated value.

    You can pass an `exc_info` three-tuple, as returned by
    [`sys.exc_info()`][sys.exc_info]. If you don't pass `exc_info`,
    [`sys.exc_info()`][sys.exc_info] will be called and the value returned
    by it used.

    In other words, if you're calling `set_exception()`, without any
    arguments, from an except block, the exception you're currently handling
    will automatically be set on the future.

    Args:
        exc_info: the encapsulated exception

    /// note | Version changed: Pykka 4.3
    Calling `set_exception()` on a future that already has a get hook
    set now raises an exception.
    ///

    """
    raise NotImplementedError

set_get_hook

set_get_hook(func: GetHookFunc[T]) -> None

Set a function to be executed when get() is called.

The function will be called when get() is called, with the timeout value as the only argument. The function's return value will be returned from get().

Parameters:

• func (GetHookFunc[T]) –

  callable accepting a timeout value, to produce return value of get()

Version added: Pykka 1.2

Version changed: Pykka 4.3

Calling set_get_hook() on a future that already has a result set now raises an exception.

Source code in src/pykka/_future.py

def set_get_hook(
    self,
    func: GetHookFunc[T],
) -> None:
    """Set a function to be executed when [`get()`][pykka.Future.get] is called.

    The function will be called when [`get()`][pykka.Future.get] is called, with the
    `timeout` value as the only argument. The function's return value will
    be returned from [`get()`][pykka.Future.get].

    Args:
        func: callable accepting a timeout value, to produce return value of
            `get()`

    /// note | Version added: Pykka 1.2
    ///

    /// note | Version changed: Pykka 4.3
    Calling `set_get_hook()` on a future that already has a result set
    now raises an exception.
    ///

    """
    self._get_hook = func

pykka.get_all

get_all(
    futures: Iterable[Future[T]],
    *,
    timeout: float | None = None,
) -> Iterable[T]

Collect all values encapsulated in the list of futures.

If timeout is not None, the method will wait for a reply for timeout seconds, and then raise pykka.Timeout.

Parameters:

• futures (Iterable[Future[T]]) –

  futures for the results to collect

• timeout (float | None, default: None ) –

  seconds to wait before timeout

Raises:

• Timeout –

  if timeout is reached

Returns:

• Iterable[T] –

  list of results

Source code in src/pykka/_future.py

def get_all(
    futures: Iterable[Future[T]],
    *,
    timeout: float | None = None,
) -> Iterable[T]:
    """Collect all values encapsulated in the list of futures.

    If `timeout` is not `None`, the method will wait for a reply for
    `timeout` seconds, and then raise [`pykka.Timeout`][pykka.Timeout].

    Args:
        futures: futures for the results to collect
        timeout: seconds to wait before timeout

    Raises:
        pykka.Timeout: if timeout is reached

    Returns:
        list of results

    """
    return [future.get(timeout=timeout) for future in futures]