--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/purple/switch.py	Tue Nov 12 21:13:13 2013 -0600
@@ -0,0 +1,74 @@
+# Copyright (C) 2013 by Brian Neal.
+# This file is part of purple, the PURPLE (Cipher Machine 97) simulation.
+# purple is released under the MIT License (see LICENSE.txt).
+
+"""This module contains the SteppingSwitch class."""
+
+
+class SteppingSwitchError(Exception):
+    """Exception class for all stepping switch errors"""
+
+
+class SteppingSwitch:
+    """This class simulates a stepping switch, the primary cryptographic element
+    in the PURPLE cipher machine.
+
+    """
+    def __init__(self, wiring, init_pos=0):
+        """Construct a SteppingSwitch from a wiring list, which must be a list
+        of lists (one list per input level). Each inner list is a list of
+        integers representing the output contacts. The initial position of the
+        switch can also be set; this defaults to 0.
+
+        """
+        self.wiring = wiring
+        self.num_contacts = len(wiring)
+        self.num_levels = len(wiring[0])
+        self.pos = init_pos
+
+        if not all(self.num_levels == len(level) for level in wiring):
+            raise SteppingSwitchError("Ragged wiring table")
+
+        if not (0 <= self.pos < self.num_contacts):
+            raise SteppingSwitchError("Illegal initial position")
+
+    def step(self):
+        """Advance the stepping switch position."""
+        self.pos = (self.pos + 1) % self.num_contacts
+
+    def __getitem__(self, level):
+        """This method is how to determine the output signal from the stepping
+        switch. The key parameter 'level' is the integer input level for the
+        incoming signal. The integer outgoing contact level is returned.
+
+        """
+        return self.wiring[self.pos][level]
+
+
+SIXES_DATA = [
+    [2, 1, 3, 5, 4, 6],
+    [6, 3, 5, 2, 1, 4],
+    [1, 5, 4, 6, 2, 3],
+    [4, 3, 2, 1, 6, 5],
+    [3, 6, 1, 4, 5, 2],
+    [2, 1, 6, 5, 3, 4],
+    [6, 5, 4, 2, 1, 3],
+    [3, 6, 1, 4, 5, 2],
+    [5, 4, 2, 6, 3, 1],
+    [4, 5, 3, 2, 1, 6],
+    [2, 1, 4, 5, 6, 3],
+    [5, 4, 6, 3, 2, 1],
+    [3, 1, 2, 6, 4, 5],
+    [4, 2, 5, 1, 3, 6],
+    [1, 6, 2, 3, 5, 4],
+    [5, 4, 3, 6, 1, 2],
+    [6, 2, 5, 3, 4, 1],
+    [2, 3, 4, 1, 5, 6],
+    [1, 2, 3, 5, 6, 4],
+    [3, 1, 6, 4, 2, 5],
+    [6, 5, 1, 2, 4, 3],
+    [1, 3, 6, 4, 2, 5],
+    [6, 4, 5, 1, 3, 2],
+    [4, 6, 1, 2, 5, 3],
+    [5, 2, 4, 3, 6, 1],
+]