WebSVN – programming – Diff – /school/cs311/proj1/proj1.py

 #       Made verbose mode into a toggle.
+#
 #   -- 2005-10-12 2000
 #       Added True/False compatibility for versions of python that
 #       are very old.
+#       Changed the "bad input" error handler to use try / except.
+#
 import sys, string
 ### Define True and False to compatible values if we are running on a version
 except:
     True = 1
     False = 0
 class automaton:
+    """The main workhorse class. Call the main_menu() function to let the user
+    enter and run an automaton."""
     def __init__(self):
         """Constructor for the automaton object"""
         self.clear()
         self.verbose = False
     def next_state(self, cur_state, letter):
         """Return the next state (as an integer) given the current state, and
         the next letter of input"""
         letter_num = self.get_letter_num(letter)
+        # There is a bad letter in the input
         if letter_num == -1 or letter_num >= self.num_letters:
-            print 'Bad letter in the input *** I WILL STAY AT THE CURRENT STATE ***'
-            return cur_state
+            raise ValueError
-            #sys.exit(1)
         next_state = self.trans_function[cur_state][letter_num]
         if self.verbose:
             print 'state %d letter %s -> state %d' % (cur_state, letter, next_state)
         return next_state
     def run_automaton(self, input_string):
         """Run the automaton through the input string given by input_string"""
-        cur_state = 0 #initial state is always q0
+        cur_state = 0 # initial state is always q0
+        try:
-        for c in input_string:
+            for c in input_string:
-            cur_state = self.next_state(cur_state, c)
+                cur_state = self.next_state(cur_state, c)
+        except ValueError:
+            print 'There was a bad letter in the input, stopping here!'
         print 'Done Running'
         print
         print 'Final State: %d' % cur_state
         print 'Accepted: %s' % (self.is_final_state(cur_state) and 'Yes' or 'No', )
 ### The "main" function
 if __name__ == '__main__':
     a = automaton()
     a.main_menu()

Subversion Repositories programming

(root)/school/cs311/proj1/proj1.py – Rev 127 → 128