Bug fix: Fix implementation of filter_keys and filter_values

These two functions do not align at all with their Kotlin counterparts, so update the implementation accordingly.

src/collektions/_mapping.py

@@ -9,46 +9,28 @@
     "map_values_to",
 ]
 
-from collections.abc import Iterable, Mapping, MutableMapping, MutableSequence
+from collections.abc import Mapping, MutableMapping
 from typing import Callable
 
 from ._types import K, R, V
 
 
 def filter_keys(
-    mapping: Mapping[K, V], predicate: Callable[[K, V], bool]
-) -> Iterable[K]:
-    """Filter ``mapping``'s key set based on ``predicate``.
-
-    The predicate function takes both the key and value from each key/value pair
-    so that filtering can be done on either.
-
-    Returns:
-        A collection of the key from each key/value pair for which predicate returns ``True``.
+    mapping: Mapping[K, V], predicate: Callable[[K], bool]
+) -> Mapping[K, V]:
     """
-    result: MutableSequence[K] = []
-    for key, value in mapping.items():
-        if predicate(key, value):
-            result.append(key)
-    return result
+    Return a new mapping of all key/value pairs from ``mapping`` where `key` satisfies ``predicate``.
+    """
+    return {k: v for k, v in mapping.items() if predicate(k)}
 
 
 def filter_values(
-    mapping: Mapping[K, V], predicate: Callable[[K, V], bool]
-) -> Iterable[V]:
-    """Filter ``mapping``'s value set based on ``predicate``.
-
-    The predicate function takes both the key and value from each key/value pair
-    so that filtering can be done on either.
-
-    Returns:
-        A collection of the value from each key/value pair for which predicate returns ``True``.
+    mapping: Mapping[K, V], predicate: Callable[[V], bool]
+) -> Mapping[K, V]:
     """
-    result: MutableSequence[V] = []
-    for key, value in mapping.items():
-        if predicate(key, value):
-            result.append(value)
-    return result
+    Return a new mapping of all key/value pairs from ``mapping`` where `value` satisfies ``predicate``.
+    """
+    return {k: v for k, v in mapping.items() if predicate(v)}
 
 
 def map_keys(mapping: Mapping[K, V], transform: Callable[[K, V], R]) -> Mapping[R, V]:

tests/test__mapping.py

@@ -8,15 +8,15 @@
 
 def test_filter_keys():
     mapping = {i: str(i) for i in range(10)}
-    expected = [0, 2, 4, 6, 8]
-    actual = filter_keys(mapping, lambda k, _: k % 2 == 0)
+    expected = {0: "0", 2: "2", 4: "4", 6: "6", 8: "8"}
+    actual = filter_keys(mapping, lambda k: k % 2 == 0)
     assert_that(actual, equal_to(expected))
 
 
 def test_filter_values():
     mapping = {i: str(i) for i in range(10)}
-    expected = ["0", "2", "4", "6", "8"]
-    actual = filter_values(mapping, lambda _, v: int(v) % 2 == 0)
+    expected = {0: "0", 2: "2", 4: "4", 6: "6", 8: "8"}
+    actual = filter_values(mapping, lambda v: int(v) % 2 == 0)
     assert_that(actual, equal_to(expected))