updated chapter 4 and appendix-A files

appendix-A/hashdiff.py

@@ -0,0 +1,20 @@
+import sys
+
+MAX_BITS = len(format(sys.maxsize, 'b'))
+print('%s-bit Python build' % (MAX_BITS + 1))
+
+def hash_diff(o1, o2):
+    h1 = '{:>0{}b}'.format(hash(o1), MAX_BITS)
+    h2 = '{:>0{}b}'.format(hash(o2), MAX_BITS)
+    diff = ''.join('!' if b1 != b2 else ' ' for b1, b2 in zip(h1, h2))
+    count = '!= {}'.format(diff.count('!'))
+    width = max(len(repr(o1)), len(repr(o2)), 8)
+    sep = '-' * (width * 2 + MAX_BITS)
+    return '{!r:{width}} {}\n{:{width}} {} {}\n{!r:{width}} {}\n{}'.format(
+    		o1, h1, ' ' * width, diff, count, o2, h2, sep, width=width)
+
+if __name__ == '__main__':
+    print(hash_diff(1, 1.0))
+    print(hash_diff(1.0, 1.0001))
+    print(hash_diff(1.0001, 1.0002))
+    print(hash_diff(1.0002, 1.0003))