updated from Atlas

11-pythonic-obj/slots.rst

@@ -0,0 +1,52 @@
+# tag::PIXEL[]
+>>> class Pixel:
+...     __slots__ = ('x', 'y')  # <1>
+...
+>>> p = Pixel()  # <2>
+>>> p.__dict__  # <3>
+Traceback (most recent call last):
+  ...
+AttributeError: 'Pixel' object has no attribute '__dict__'
+>>> p.x = 10  # <4>
+>>> p.y = 20
+>>> p.color = 'red'  # <5>
+Traceback (most recent call last):
+  ...
+AttributeError: 'Pixel' object has no attribute 'color'
+
+# end::PIXEL[]
+
+# tag::OPEN_PIXEL[]
+>>> class OpenPixel(Pixel):  # <1>
+...     pass
+...
+>>> op = OpenPixel()
+>>> op.__dict__  # <2>
+{}
+>>> op.x = 8  # <3>
+>>> op.__dict__  # <4>
+{}
+>>> op.x  # <5>
+8
+>>> op.color = 'green'  # <6>
+>>> op.__dict__  # <7>
+{'color': 'green'}
+
+# end::OPEN_PIXEL[]
+
+# tag::COLOR_PIXEL[]
+>>> class ColorPixel(Pixel):
+...    __slots__ = ('color',)  # <1>
+>>> cp = ColorPixel()
+>>> cp.__dict__  # <2>
+Traceback (most recent call last):
+  ...
+AttributeError: 'ColorPixel' object has no attribute '__dict__'
+>>> cp.x = 2
+>>> cp.color = 'blue'  # <3>
+>>> cp.flavor = 'banana'
+Traceback (most recent call last):
+  ...
+AttributeError: 'ColorPixel' object has no attribute 'flavor'
+
+# end::COLOR_PIXEL[]