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‎docs/index.rst

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pages/functions.rst
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pages/curry.rst
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pages/types.rst
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pages/transducers.rst
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.. toctree::
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:maxdepth: 2

‎docs/pages/transducers.rst

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.. transducers:
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Transducers
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===========
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API Reference
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-------------
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.. automodule:: returns.transducers.transducers
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:members:
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.. autofunction:: returns.transducers.tmap
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.. autofunction:: returns.transducers.tfilter

‎returns/transducers/__init__.py

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from returns.transducers.tfilter import tfilter as tfilter
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from returns.transducers.tmap import tmap as tmap
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from returns.transducers.transducers import Missing as Missing
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from returns.transducers.transducers import Reduced as Reduced
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from returns.transducers.transducers import transduce as transduce
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from returns.transducers.transducers import treduce as treduce

‎returns/transducers/tfilter.py

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from typing import Callable, TypeVar
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_ValueType = TypeVar('_ValueType')
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_AccValueType = TypeVar('_AccValueType')
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def tfilter(
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predicate: Callable[[_ValueType], bool],
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) -> Callable[
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[Callable[[_AccValueType, _ValueType], _AccValueType]],
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Callable[[_AccValueType, _ValueType], _AccValueType],
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]:
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"""
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:py:func:`filter <filter>` implementation on a transducer form.
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.. code:: python
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>>> from typing import List
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>>> from returns.transducers import tfilter, treduce
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>>> def is_even(number: int) -> bool:
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... return number % 2 == 0
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>>> def append(collection: List[int], item: int) -> List[int]:
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... collection.append(item)
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... return collection
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>>> my_list = [0, 1, 2, 3, 4, 5, 6]
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>>> xform = tfilter(is_even)(append)
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>>> assert treduce(xform, my_list, []) == [0, 2, 4, 6]
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"""
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def reducer(
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step: Callable[[_AccValueType, _ValueType], _AccValueType],
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) -> Callable[[_AccValueType, _ValueType], _AccValueType]:
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def filter_(acc: _AccValueType, value: _ValueType) -> _AccValueType:
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if predicate(value):
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return step(acc, value)
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return acc
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return filter_
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return reducer

‎returns/transducers/tmap.py

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from typing import Callable, TypeVar
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_ValueType = TypeVar('_ValueType')
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_NewValueType = TypeVar('_NewValueType')
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_AccValueType = TypeVar('_AccValueType')
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def tmap(
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function: Callable[[_ValueType], _NewValueType],
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) -> Callable[
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[Callable[[_AccValueType, _NewValueType], _AccValueType]],
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Callable[[_AccValueType, _ValueType], _AccValueType],
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]:
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"""
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A map implementation on a transducer form.
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.. code:: python
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>>> from typing import List
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>>> from returns.transducers import tmap, treduce
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>>> def add_one(number: int) -> int:
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... return number + 1
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>>> def append(collection: List[int], item: int) -> List[int]:
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... collection.append(item)
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... return collection
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>>> my_list = [0, 1]
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>>> xformaa = tmap(add_one)(append)
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>>> assert treduce(xformaa, my_list, []) == [1, 2]
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"""
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def reducer(
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step: Callable[[_AccValueType, _NewValueType], _AccValueType],
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) -> Callable[[_AccValueType, _ValueType], _AccValueType]:
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def map_(acc: _AccValueType, value: _ValueType) -> _AccValueType:
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return step(acc, function(value))
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return map_
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return reducer

‎returns/transducers/transducers.py

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from typing import (
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Any,
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Callable,
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Generic,
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Iterable,
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Optional,
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TypeVar,
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final,
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overload,
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)
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from returns.primitives.types import Immutable
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_ValueType = TypeVar('_ValueType')
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_NewValueType = TypeVar('_NewValueType')
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_AccValueType = TypeVar('_AccValueType')
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@final
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class Reduced(Immutable, Generic[_ValueType]):
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"""
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Sentinel for early termination inside transducer.
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.. code:: python
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>>> from returns.transducers import tmap, transduce, Reduced
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>>> def add_one(number: int) -> int:
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... return number + 1
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>>> def add(acc: int, number: int) -> int:
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... if acc == 3:
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... return Reduced(acc)
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... return acc + number
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>>> my_list = [0, 1, 2]
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>>> assert transduce(tmap(add_one), add, 0, my_list) == 3
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"""
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__slots__ = ('_inner_value',)
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_inner_value: _ValueType
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def __init__(self, inner_value: _ValueType) -> None:
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"""Encapsulates the value from early reduce termination."""
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object.__setattr__(self, '_inner_value', inner_value) # noqa: WPS609
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@property
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def value(self) -> _ValueType: # noqa: WPS110
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"""Returns the value from early reduce termination."""
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return self._inner_value
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@final
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class _Missing(Immutable):
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"""Represents a missing value for reducers."""
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__slots__ = ('_instance',)
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_instance: Optional['_Missing'] = None
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def __new__(cls, *args: Any, **kwargs: Any) -> '_Missing':
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if cls._instance is None:
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cls._instance = object.__new__(cls) # noqa: WPS609
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return cls._instance
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#: A singleton representing any missing value
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Missing = _Missing()
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def transduce(
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xform: Callable[
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[Callable[[_AccValueType, _ValueType], _AccValueType]],
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Callable[[_AccValueType, _ValueType], _AccValueType],
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],
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reducing_function: Callable[[_AccValueType, _ValueType], _AccValueType],
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initial: _AccValueType,
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iterable: Iterable[_ValueType],
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) -> _AccValueType:
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"""
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Process information with transducers.
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.. code:: python
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>>> from returns.transducers import tmap, transduce
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>>> def add_one(number: int) -> int:
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... return number + 1
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>>> def add(acc: int, number: int) -> int:
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... return acc + number
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>>> my_list = [0, 1, 2]
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>>> assert transduce(tmap(add_one), add, 0, my_list) == 6
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"""
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reducer = xform(reducing_function)
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return treduce(reducer, iterable, initial)
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@overload
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def treduce(
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function: Callable[[_ValueType, _ValueType], _ValueType],
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iterable: Iterable[_ValueType],
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initial: _Missing = Missing,
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) -> _ValueType:
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"""Reduce without an initial value."""
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@overload
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def treduce(
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function: Callable[[_AccValueType, _ValueType], _AccValueType],
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iterable: Iterable[_ValueType],
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initial: _AccValueType,
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) -> _AccValueType:
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"""Reduce with an initial value."""
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def treduce(function, iterable, initial=Missing):
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"""
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A rewritten version of :func:`reduce <functools.reduce>`.
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This version considers some features borrowed from Clojure:
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- Early termination
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- Function initializer [TODO]
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You can use it as a normal reduce if you want:
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.. code:: python
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>>> from returns.transducers import treduce
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>>> def add(acc: int, value: int) -> int:
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... return acc + value
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>>> assert treduce(add, [1, 2, 3]) == 6
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"""
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it = iter(iterable)
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if initial is Missing:
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try:
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acc_value = next(it)
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except StopIteration:
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raise TypeError(
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'reduce() of empty iterable with no initial value',
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) from None
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else:
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acc_value = initial
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for value in it: # noqa: WPS110
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acc_value = function(acc_value, value)
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if isinstance(acc_value, Reduced):
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return acc_value.value
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return acc_value

‎setup.cfg

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returns/methods/__init__.py: F401, WPS201
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returns/pipeline.py: F401
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returns/context/__init__.py: F401, WPS201
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returns/transducers/__init__.py: F401
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# Disable some quality checks for the most heavy parts:
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returns/io.py: WPS402
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returns/iterables.py: WPS234
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returns/primitives/asserts.py: S101
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# Some rules cannot be applied to context:
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returns/context/*.py: WPS201, WPS204, WPS226, WPS326, WPS430
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# Some rules cannot be applied to transducers:
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returns/transducers/*.py: WPS110, WPS430
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# We allow `futures` to do attribute access:
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returns/future.py: WPS437
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returns/_internal/futures/*.py: WPS204, WPS433, WPS437

‎tests/test_transducers/test_transducers/test_missing_singleton.py

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from returns.transducers.transducers import _Missing
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def test_missing_singleton():
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"""Ensures `_Missing` is a singleton."""
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assert _Missing() is _Missing()

‎tests/test_transducers/test_transducers/test_treduce.py

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import pytest
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from returns.transducers import treduce
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def test_reduce():
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"""Should fail when iterable is empty and non initial value is given."""
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with pytest.raises(TypeError):
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treduce(lambda acc, value: acc + value, []) # noqa: WPS110

‎typesafety/test_transducers/test_tfilter.yml

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- case: tfilter
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disable_cache: false
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main: |
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from returns.transducers import tfilter
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def is_even(number: int) -> bool:
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...
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reveal_type(tfilter(is_even)) # N: Revealed type is 'def [_AccType] (def (_AccType`-2, builtins.int*) -> _AccType`-2) -> def (_AccType`-2, builtins.int*) -> _AccType`-2'
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- case: tfilter_reducer
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disable_cache: false
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main: |
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from typing import List
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from returns.transducers import tfilter
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def is_even(number: int) -> bool:
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...
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def append(collection: List[int], item: int) -> List[int]:
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...
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reveal_type(tfilter(is_even)(append)) # N: Revealed type is 'def (builtins.list*[builtins.int], builtins.int) -> builtins.list*[builtins.int]'
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- case: tfilter_reducer_filter_
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disable_cache: false
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main: |
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from typing import List
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from returns.transducers import tfilter, reduce
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def is_even(number: int) -> bool:
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...
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def append(collection: List[int], item: int) -> List[int]:
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...
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my_list: List[int]
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reveal_type(tfilter(is_even)(append)(my_list, 2)) # N: Revealed type is 'builtins.list*[builtins.int]'
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- case: tfilter_composition_one
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disable_cache: false
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main: |
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from typing import List
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from returns.transducers import tfilter, reduce
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def is_even(number: int) -> bool:
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...
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def append(collection: List[int], item: int) -> List[int]:
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...
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composed = tfilter(is_even)(tfilter(is_even)(append))
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reveal_type(composed) # N: Revealed type is 'def (builtins.list*[builtins.int], builtins.int) -> builtins.list*[builtins.int]'
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- case: tfilter_composition_two
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disable_cache: false
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main: |
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from typing import List
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from returns.transducers import tfilter, reduce
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def is_even(number: int) -> bool:
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...
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def append(collection: List[int], item: int) -> List[int]:
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...
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composed = tfilter(is_even)(tfilter(is_even)(append))
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my_list: List[int]
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reveal_type(composed(my_list, 42)) # N: Revealed type is 'builtins.list*[builtins.int]'

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