Merge ea87605 into 562dddc

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "zninit"
-version = "0.1.6"
+version = "0.1.7"
 description = "Descriptor based dataclass implementation"
 authors = ["zincwarecode <zincwarecode@gmail.com>"]
 license = "Apache-2.0"

tests/test_descriptor.py

@@ -146,3 +146,36 @@ def test_get_desc_values():
 
     assert desc1_1.__get__(self) == "Hello"
     assert desc1_2.__get__(self) == "World"
+
+
+class FrozenExample:
+    """ZnInit Frozen Descriptor."""
+
+    value = Descriptor(frozen=True)
+
+
+def test_frozen_descriptor():
+    """Test a frozen descriptor."""
+    example = FrozenExample()
+    example.value = 42
+    with pytest.raises(TypeError):
+        example.value = 25
+    assert example.value == 42
+
+    # Running twice is a test.
+    example = FrozenExample()
+    example.value = 42
+    with pytest.raises(TypeError):
+        example.value = 25
+    assert example.value == 42
+
+
+class WithMetadata:
+    """ZnInit Descriptor with metadata."""
+
+    value = Descriptor(metadata={"foo": "bar"})
+
+
+def test_descriptor_metadata():
+    """Test a descriptor with metadata."""
+    assert WithMetadata.value.metadata["foo"] == "bar"

tests/test_i_zninit.py

@@ -1,4 +1,6 @@
 """General 'ZnInit' integration tests."""
+import pytest
+
 import zninit
 
 
@@ -14,10 +16,37 @@ class ExampleCls(zninit.ZnInit, metaclass=GetItemMeta):
     """Example 'ZnInit' with metaclass."""
 
     parameter = zninit.Descriptor()
+    frozen_parameter = zninit.Descriptor(None, frozen=True)
 
 
 def test_ExampleCls():
     """Test 'ZnInit' with a metaclass."""
     example = ExampleCls(parameter=25)
     assert example.parameter == 25
     assert ExampleCls[42] == 42
+
+
+def test_frozen_parameter():
+    """Test frozen parameter."""
+    example = ExampleCls(parameter=18, frozen_parameter=42)
+    assert example.frozen_parameter == 42
+    with pytest.raises(TypeError):
+        example.frozen_parameter = 43
+
+    example = ExampleCls(parameter=18, frozen_parameter=42)
+    assert example.frozen_parameter == 42
+    with pytest.raises(TypeError):
+        example.frozen_parameter = 43
+
+
+def test_frozen_parameter_default():
+    """Test frozen_parameter with default value."""
+    example = ExampleCls(parameter=18)
+    assert example.frozen_parameter is None
+    with pytest.raises(TypeError):
+        example.frozen_parameter = 43
+
+    example = ExampleCls(parameter=18, frozen_parameter=42)
+    assert example.frozen_parameter == 42
+    with pytest.raises(TypeError):
+        example.frozen_parameter = 43

tests/test_zninit.py

@@ -5,4 +5,4 @@
 
 def test_version():
     """Test the installed version."""
-    assert zninit.__version__ == "0.1.6"
+    assert zninit.__version__ == "0.1.7"

zninit/descriptor/__init__.py

@@ -5,6 +5,7 @@
 import functools
 import sys
 import typing
+import weakref
 
 with contextlib.suppress(ImportError):
     import typeguard
@@ -18,7 +19,7 @@ class Empty:  # pylint: disable=too-few-public-methods
     """
 
 
-class Descriptor:
+class Descriptor:  # pylint: disable=too-many-instance-attributes
     """Simple Python Descriptor that allows adding.
 
     This class allows to add metadata to arbitrary class arguments:
@@ -53,6 +54,8 @@ def __init__(
         name="",
         use_repr: bool = True,
         check_types: bool = False,
+        metadata: dict = None,
+        frozen: bool = False,
     ):  # pylint: disable=too-many-arguments
         """Define a Descriptor object.
 
@@ -71,13 +74,20 @@ def __init__(
             descriptor should be used in the __repr__ string.
         check_types: bool, default=False
             Check the type when using __set__ against the type annotation.
+        frozen: bool, default=False
+            Freeze the attribute after the first __set__ call.
+        metadata: dict, default=None
+            additional metadata for the descriptor.
         """
         self._default = default
         self._owner = owner
         self._instance = instance
         self._name = name
         self.use_repr = use_repr
         self.check_types = check_types
+        self.metadata = metadata or {}
+        self.frozen = frozen
+        self._frozen = weakref.WeakKeyDictionary()
         if check_types and ("typeguard" not in sys.modules):
             raise ImportError(
                 "Need to install 'pip install zninit[typeguard]' for type checking."
@@ -117,12 +127,11 @@ def annotation(self):
         except AttributeError:
             annotations = {}
 
-        if self.check_types:
-            if self.name not in annotations:
-                raise KeyError(
-                    f"Could not find 'annotation' for {self.name} in '{self.owner}' with"
-                    " 'check_types=True'"
-                )
+        if self.check_types and self.name not in annotations:
+            raise KeyError(
+                f"Could not find 'annotation' for {self.name} in '{self.owner}' with"
+                " 'check_types=True'"
+            )
         return annotations.get(self.name)
 
     def __set_name__(self, owner, name):
@@ -149,12 +158,16 @@ def __get__(self, instance, owner=None):
 
     def __set__(self, instance, value):
         """Save value to instance.__dict__."""
+        if self._frozen.get(instance, False):
+            raise TypeError(f"Frozen attribute '{self.name}' can not be changed.")
         if self.check_types:
             typeguard.check_type(
                 argname=self.name, value=value, expected_type=self.annotation
             )
         self._instance = instance
         instance.__dict__[self.name] = value
+        if self.frozen:
+            self._frozen[instance] = True
 
 
 DescriptorTypeT = typing.TypeVar("DescriptorTypeT", bound=Descriptor)