Add pathlib brain to handle .parents inference (#1442)

Co-authored-by: Daniël van Noord <[email protected]>
Co-authored-by: Marc Mueller <[email protected]>

Author: 3 people

ChangeLog

@@ -54,6 +54,10 @@ Release date: TBA
 
   Closes #1403
 
+* Add ``pathlib`` brain to handle ``pathlib.PurePath.parents`` inference.
+
+  Closes PyCQA/pylint#5783
+
 * Fix test for Python ``3.11``. In some instances ``err.__traceback__`` will
   be uninferable now.
 

astroid/brain/brain_pathlib.py

@@ -0,0 +1,53 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/astroid/blob/main/CONTRIBUTORS.txt
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+
+from astroid import bases, context, inference_tip, nodes
+from astroid.builder import _extract_single_node
+from astroid.exceptions import InferenceError, UseInferenceDefault
+from astroid.manager import AstroidManager
+
+PATH_TEMPLATE = """
+from pathlib import Path
+Path
+"""
+
+
+def _looks_like_parents_subscript(node: nodes.Subscript) -> bool:
+    if not (
+        isinstance(node.value, nodes.Name)
+        or isinstance(node.value, nodes.Attribute)
+        and node.value.attrname == "parents"
+    ):
+        return False
+
+    try:
+        value = next(node.value.infer())
+    except (InferenceError, StopIteration):
+        return False
+    return (
+        isinstance(value, bases.Instance)
+        and isinstance(value._proxied, nodes.ClassDef)
+        and value.qname() == "pathlib._PathParents"
+    )
+
+
+def infer_parents_subscript(
+    subscript_node: nodes.Subscript, ctx: context.InferenceContext | None = None
+) -> Iterator[bases.Instance]:
+    if isinstance(subscript_node.slice, nodes.Const):
+        path_cls = next(_extract_single_node(PATH_TEMPLATE).infer())
+        return iter([path_cls.instantiate_class()])
+
+    raise UseInferenceDefault
+
+
+AstroidManager().register_transform(
+    nodes.Subscript,
+    inference_tip(infer_parents_subscript),
+    _looks_like_parents_subscript,
+)

tests/unittest_brain_pathlib.py

@@ -0,0 +1,86 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/astroid/blob/main/CONTRIBUTORS.txt
+
+
+import astroid
+from astroid import bases
+from astroid.const import PY310_PLUS
+from astroid.util import Uninferable
+
+
+def test_inference_parents() -> None:
+    """Test inference of ``pathlib.Path.parents``."""
+    name_node = astroid.extract_node(
+        """
+    from pathlib import Path
+
+    current_path = Path().resolve()
+    path_parents = current_path.parents
+    path_parents
+    """
+    )
+    inferred = name_node.inferred()
+    assert len(inferred) == 1
+    assert isinstance(inferred[0], bases.Instance)
+    assert inferred[0].qname() == "pathlib._PathParents"
+
+
+def test_inference_parents_subscript_index() -> None:
+    """Test inference of ``pathlib.Path.parents``, accessed by index."""
+    parents, path = astroid.extract_node(
+        """
+    from pathlib import Path
+
+    current_path = Path().resolve()
+    path_parents = current_path.parents
+    path_parents  #@
+    path_parents[2]  #@
+    """
+    )
+    inferred = parents.inferred()
+    assert len(inferred) == 1
+    assert isinstance(inferred[0], bases.Instance)
+    assert inferred[0].qname() == "pathlib._PathParents"
+
+    inferred = path.inferred()
+    assert len(inferred) == 1
+    assert isinstance(inferred[0], bases.Instance)
+    assert inferred[0].qname() == "pathlib.Path"
+
+
+def test_inference_parents_subscript_slice() -> None:
+    """Test inference of ``pathlib.Path.parents``, accessed by slice."""
+    name_node = astroid.extract_node(
+        """
+    from pathlib import Path
+
+    current_path = Path().resolve()
+    parent_path = current_path.parents[:2]
+    parent_path
+    """
+    )
+    inferred = name_node.inferred()
+    assert len(inferred) == 1
+    if PY310_PLUS:
+        assert isinstance(inferred[0], bases.Instance)
+        assert inferred[0].qname() == "builtins.tuple"
+    else:
+        assert inferred[0] is Uninferable
+
+
+def test_inference_parents_subscript_not_path() -> None:
+    """Test inference of other ``.parents`` subscripts is unaffected."""
+    name_node = astroid.extract_node(
+        """
+    class A:
+        parents = 42
+
+    c = A()
+    error = c.parents[:2]
+    error
+    """
+    )
+    inferred = name_node.inferred()
+    assert len(inferred) == 1
+    assert inferred[0] is Uninferable