add Partition #1905

CHANGELOG.md

@@ -14,6 +14,7 @@ See [0Ver](https://0ver.org/).
 - Improve inference of `ResultLike` objects when exception catching
  decorator is applied with explicit exception types
 - Add picky exceptions to `impure_safe` decorator like `safe` has. Issue #1543
+- Add partition function to result module. Issue #1905
 
 ### Misc
 

docs/pages/result.rst

@@ -138,6 +138,18 @@ argument that lead to that exception.
 
  This decorator works only with functions that has just one argument.
 
+partition
+~~~~~~~
+
+:func:`partition <returns.result.partition>` is used to convert
+list of ``Result`` instances to a tuple of two lists: successes and failures.
+ .. code:: python
+
+ >>> from returns.result import Failure, Success, partition
+ >>> results = [Success(1), Failure(2), Success(3)]
+ >>> partition(results)
+ ([Success(1), Success(3)], [Failure(2)])
+
 FAQ
 ---
 

returns/result.py

@@ -6,6 +6,7 @@
  Any,
  Callable,
  Generator,
+ Iterable,
  Iterator,
  List,
  Optional,
@@ -603,3 +604,27 @@ def decorator(arg: _FirstType) -> Result[_NewValueType, _FirstType]:
  return Failure(arg)
 
  return decorator
+
+
+def partition(resulsts: Iterable[Result[_ValueType, _ErrorType]]) -> tuple[
+ List[Success], List[Failure],
+]:
+ """
+ Partition a list of results into successes and failures. Preserves order.
+
+ .. code:: python
+
+ >>> from returns.result import Failure, Success, partition
+ >>> results = [Success(1), Failure(2), Success(3)]
+ >>> partition(results)
+ ([Success(1), Success(3)], [Failure(2)])
+
+ """
+ successes = []
+ failures = []
+ for res in resulsts:
+ if isinstance(res, Success):
+ successes.append(res)
+ else:
+ failures.append(res)
+ return successes, failures

tests/test_result/test_result_partition.py

@@ -0,0 +1,15 @@
+
+import pytest
+
+from returns.result import Failure, Success, partition
+
+
+@pytest.mark.parametrize(('containers', 'expected'), [
+ (
+ [Success(1), (Success(2), Failure(None))],
+ ([Success(1), Success(2)], [Failure(None)]),
+ ),
+])
+def test_partition(containers, expected):
+ """Test partition function."""
+ assert partition(containers) == expected

typesafety/test_result/test_partition.yml

@@ -0,0 +1,13 @@
+- case: partition_no_params
+ disable_cache: false
+ main: |
+ from returns.result import Success, Failure, partition
+
+ def some(arg: int) -> tuple[list[Success],list[Failure]]:
+ suc = Sucess(arg)
+ failure = Failure('test')
+
+ return partition([suc, failure])
+
+ reveal_type(some(1)) # N: Revealed type is "tuple[returns.result.Success[builtin.int],returns.result.Failure[builtin.str]]"
+