getnested

src/mrpro/utils/__init__.py

@@ -10,10 +10,14 @@
 from mrpro.utils.split_idx import split_idx
 from mrpro.utils.reshape import broadcast_right, unsqueeze_left, unsqueeze_right, reduce_view, reshape_broadcasted, ravel_multi_index, unsqueeze_tensors_left, unsqueeze_tensors_right
 from mrpro.utils.TensorAttributeMixin import TensorAttributeMixin
+from mrpro.utils.getnested import getnestedattr, getnesteditem
+
 __all__ = [
     "TensorAttributeMixin",
     "broadcast_right",
     "fill_range_",
+    "getnestedattr",
+    "getnesteditem",
     "ravel_multi_index",
     "reduce_view",
     "remove_repeat",

src/mrpro/utils/getnested.py

@@ -0,0 +1,76 @@
+"""Get a nested attribute."""
+
+from collections.abc import Mapping
+from typing import TypeVar, cast, overload
+
+T = TypeVar('T')
+
+
+@overload
+def getnestedattr(obj: object, *attrs: str, default: None = ..., return_type: None = ...) -> object | None: ...
+@overload
+def getnestedattr(obj: object, *attrs: str, default: T = ..., return_type: None = ...) -> T: ...
+@overload
+def getnestedattr(obj: object, *attrs: str, default: None = ..., return_type: type[T] = ...) -> T | None: ...
+@overload
+def getnestedattr(obj: object, *attrs: str, default: T = ..., return_type: type[T] = ...) -> T: ...
+
+
+def getnestedattr(obj: object, *attrs: str, default: T | None = None, return_type: type[T] | None = None) -> T | None:
+    """
+    Get a nested attribute, or return a default if any step fails.
+
+    Parameters
+    ----------
+    obj
+        object to get attribute from
+    attrs
+        attribute names to get
+    default
+        value to return if any step fails
+    return_type
+        type to cast the result to (only for type hinting)
+    """
+    if return_type is not None and default is not None and not isinstance(default, return_type):
+        raise TypeError('default must be of the same type as return_type')
+    for attr in attrs:
+        try:
+            obj = getattr(obj, attr)
+        except AttributeError:
+            return default
+    return cast(T, obj)
+
+
+@overload
+def getnesteditem(obj: Mapping, *items: str, default: None = ..., return_type: None = ...) -> object | None: ...
+@overload
+def getnesteditem(obj: Mapping, *items: str, default: T = ..., return_type: None = ...) -> T: ...
+@overload
+def getnesteditem(obj: Mapping, *items: str, default: None = ..., return_type: type[T] = ...) -> T | None: ...
+@overload
+def getnesteditem(obj: Mapping, *items: str, default: T = ..., return_type: type[T] = ...) -> T: ...
+
+
+def getnesteditem(obj: Mapping, *items: str, default: T | None = None, return_type: type[T] | None = None) -> T | None:
+    """
+    Get a nested item, or return a default if any step fails.
+
+    Parameters
+    ----------
+    obj
+        object to get attribute from
+    items
+        item names to get
+    default
+        value to return if any step fails
+    return_type
+        type to cast the result to (only for type hinting)
+    """
+    if return_type is not None and default is not None and not isinstance(default, return_type):
+        raise TypeError('default must be of the same type as return_type')
+    for item in items:
+        try:
+            obj = obj[item]
+        except (KeyError, TypeError):
+            return default
+    return cast(T, obj)

tests/utils/test_getnested.py

@@ -0,0 +1,86 @@
+from dataclasses import dataclass, field
+
+import pytest
+from mrpro.utils import getnestedattr, getnesteditem
+from typing_extensions import assert_type
+
+
+@dataclass
+class C:
+    """Test class for getnestedattr."""
+
+    c: int = 1
+
+
+@dataclass
+class B:
+    """Test class for getnestedattr."""
+
+    b: C = field(default_factory=C)
+
+
+@dataclass
+class A:
+    """Test class for getnestedattr."""
+
+    a: B = field(default_factory=B)
+
+
+def test_getnestedattr_value() -> None:
+    """Test getnestedattr with a valid path."""
+    obj = A()
+    actual = getnestedattr(obj, 'a', 'b', 'c')
+    assert actual == 1
+
+
+def test_getnestedattr_default() -> None:
+    """Test getnestedattr with a missing path and a default value."""
+    obj = A()
+    actual = getnestedattr(obj, 'a', 'doesnotexist', 'c', default=2)
+    assert_type(actual, int)
+    assert actual == 2
+
+
+def test_getnestedattr_type() -> None:
+    """Test getnestedattr with a missing path no default value, but a return type."""
+    obj = A()
+    actual = getnestedattr(obj, 'a', 'doesnotexist', 'c', return_type=int)
+    assert_type(actual, int | None)
+    assert actual is None
+
+
+def test_getnestedattr_default_type_error() -> None:
+    """Test getnestedattr with a default value and a return type that do not match."""
+    obj = A()
+    with pytest.raises(TypeError):
+        getnestedattr(obj, 'a', default=2, return_type=str)
+
+
+def test_getnesteditem_value() -> None:
+    """Test getnesteditem with a valid path."""
+    obj = {'a': {'b': {'c': 1}}}
+    actual = getnesteditem(obj, 'a', 'b', 'c')
+    assert actual == 1
+
+
+def test_getnesteditem_default() -> None:
+    """Test getnesteditem with a missing path and a default value."""
+    obj = {'a': {'b': {'c': 1}}}
+    actual = getnesteditem(obj, 'a', 'doesnotexist', 'c', default=2)
+    assert_type(actual, int)
+    assert actual == 2
+
+
+def test_getnesteditem_type() -> None:
+    """Test getnesteditem with a missing path no default value, but a return type."""
+    obj = {'a': {'b': {'c': 1}}}
+    actual = getnesteditem(obj, 'a', 'doesnotexist', 'c', return_type=int)
+    assert_type(actual, int | None)
+    assert actual is None
+
+
+def test_getnesteditem_default_type_error() -> None:
+    """Test getnesteditem with a default value and a return type that do not match."""
+    obj = {'a': {'b': {'c': 1}}}
+    with pytest.raises(TypeError):
+        getnesteditem(obj, 'a', default=2, return_type=str)