candidate for the all-important first chapter code sample

humansize.py

@@ -0,0 +1,36 @@
+from optparse import OptionParser
+
+SUFFIXES = ('KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB')
+MULTIPLES = {True: 1024, False: 1000}
+
+def human_size(size, use_binary_multiples=True):
+    """Convert a file size to human-readable form.
+
+    Keyword arguments:
+    size -- file size in bytes
+    use_binary_multiples -- if False, use multiples of 1000
+                            if True, use multiples of 1024 (default=True)
+
+    Returns: string
+
+    """
+    multiple = MULTIPLES[use_binary_multiples]
+    for suffix in SUFFIXES:
+        size /= multiple
+        if size < multiple:
+            return "{0:.1f} {1}".format(size, suffix)
+    return "Too large to contemplate!"
+
+if __name__ == "__main__":
+    parser = OptionParser()
+    parser.add_option("-d", "--decimal",
+                      action="store_false",
+                      dest="binary_multiples",
+                      default=True,
+                      help="use multiples of 1000 instead of 1024")
+    (options, args) = parser.parse_args()
+    if args:
+        print(human_size(int(args[0]), options.binary_multiples))
+    else:
+        parser.print_help()
+