updated chapter 4 and appendix-A files

appendix-A/mem_test.py

@@ -0,0 +1,24 @@
+import importlib
+import sys
+import resource
+
+NUM_VECTORS = 10**7
+
+if len(sys.argv) == 2:
+    module_name = sys.argv[1].replace('.py', '')
+    module = importlib.import_module(module_name)
+else:
+    print('Usage: {} <vector-module-to-test>'.format())
+    sys.exit(1)
+
+fmt = 'Selected Vector2d type: {.__name__}.{.__name__}'
+print(fmt.format(module, module.Vector2d))
+
+mem_init = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+print('Creating {:,} Vector2d instances'.format(NUM_VECTORS))
+
+vectors = [module.Vector2d(3.0, 4.0) for i in range(NUM_VECTORS)]
+
+mem_final = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+print('Initial RAM usage: {:14,}'.format(mem_init))
+print('  Final RAM usage: {:14,}'.format(mem_final))