added classex.AttributeDescriptor

ioex/classex.py

@@ -0,0 +1,10 @@
+class AttributeDescriptor(object):
+
+    def __init__(self, name):
+        self._name = name
+
+    def __get__(self, instance, owner):
+        return getattr(instance, self._name)
+
+    def __set__(self, instance, value):
+        setattr(instance, self._name, value)

tests/classex/test_attribute_descriptor.py

@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+import pytest
+
+from ioex.classex import AttributeDescriptor
+
+
+class Foo(object):
+
+    desc = AttributeDescriptor('attr')
+
+    def __init__(self, default):
+        self.attr = default
+
+
+def test_set_get_attribute():
+    obj = Foo(1)
+    assert 1 == obj.attr
+    assert 1 == obj.desc
+    obj.attr = 2
+    assert 2 == obj.attr
+    assert 2 == obj.desc
+    obj.desc = 3
+    assert 3 == obj.attr
+    assert 3 == obj.desc
+
+
+def test_multiple_instances():
+    a = Foo('a')
+    b = Foo('b')
+    assert 'a' == a.desc
+    assert 'b' == b.desc
+    a.desc = a.desc.upper()
+    b.desc = b.desc.upper()
+    assert 'A' == a.desc
+    assert 'B' == b.desc
+
+
+class Bar(object):
+
+    a = AttributeDescriptor('_a')
+    A = AttributeDescriptor('_a')
+    b = AttributeDescriptor('_b')
+
+
+def test_multiple_attributes():
+    obj = Bar()
+    obj._a = 'a'
+    obj._b = 'b'
+    assert 'a' == obj.a
+    assert 'a' == obj.A
+    assert 'b' == obj.b
+    obj.A = 'A'
+    obj.b = 'B'
+    assert 'A' == obj.a
+    assert 'A' == obj.A
+    assert 'B' == obj.b
+
+
+class IntAttr(AttributeDescriptor):
+
+    def __set__(self, instance, value):
+        if not isinstance(value, int):
+            raise TypeError()
+        else:
+            super(IntAttr, self).__set__(instance, value)
+
+class Qux(object):
+
+    desc = IntAttr('attr')
+
+def test_subclass():
+    obj = Qux()
+    obj.attr = 'first'
+    assert 'first' == obj.attr
+    assert 'first' == obj.desc
+    obj.desc = 42
+    assert 42 == obj.attr
+    assert 42 == obj.desc
+    with pytest.raises(TypeError):
+        obj.desc = 3.14