C.3 Object diagrams

Figure 19.6 Figure C.4: Object diagram. 

 

numbers = [17, 123]
empty = []
 
lumpy.object_diagram()

Figure 19.5 shows the result. Lists are represented by a box that shows the indices mapping to the elements. This representation is slightly misleading, since indices are not actually part of the list, but I think they make the diagram easier to read. The empty list is represented by an empty box.

And here’s an example showing the dictionaries from Dictionaries and lists. You can download it from http://thinkpython.com/code/lumpy_demo4.py.

from swampy.Lumpy import Lumpy
 
lumpy = Lumpy()
lumpy.make_reference()
 
hist = histogram('parrot')
inverse = invert_dict(hist)
 
lumpy.object_diagram()

Figure 19.6 shows the result. hist is a dictionary that maps from characters (single-letter strings) to integers; inverse maps from integers to lists of strings.

This example generates an object diagram for Point and Rectangle objects, as in Copying. You can download it from http://thinkpython.com/code/lumpy_demo5.py.

import copyfrom swampy.Lumpy import Lumpy

Figure 19.7 Figure C.5: Object diagram. 

 

Figure 19.8 Figure C.6: Object diagram. 

 

lumpy = Lumpy()
lumpy.make_reference()
 
box = Rectangle()
box.width = 100.0
box.height = 200.0
box.corner = Point()
box.corner.x = 0.0
box.corner.y = 0.0
 
box2 = copy.copy(box)
 
lumpy.object_diagram()

Figure 19.7 shows the result. copy.copy make a shallow copy, so box and box2 have their own width and height, but they share the same embedded Point object. This kind of sharing is usually fine with immutable objects, but with mutable types, it is highly errorprone.