introduce base class for exceptions

ail.py

@@ -18,7 +18,7 @@
 
    --help              print this help message and exit
 
-:version: $Revision: 1.26 $  
+:version: $Revision: 1.26 $
 :author: Logilab
 """
 
@@ -64,8 +64,8 @@
             input = raw_input('>>> ')
             try:
                 answer = brain.think(input)
-            except NoRewriteError :
-                answer = '...'
+            except AilError, exc:
+                answer = 'Error: %s' % exc
             if answer.startswith('assert') :
                 print "I learned that", answer[6:]
             elif answer.startswith('search') :
@@ -128,6 +128,9 @@
     """handler function for rgx.sub to transform \n to %(n-1)s"""
     return r'%%(%s)s' % (int(match.group(1)) - 1)
 
-class NoRewriteError(Exception):
+class AilError(Exception):
+    """base ail exception"""
+
+class NoRewriteError(AilError):
     """exception used when no more rewrite rules are available"""
 
@@ -132,5 +135,5 @@
     """exception used when no more rewrite rules are available"""
 
-class InfiniteCycleError(Exception):
+class InfiniteCycleError(AilError):
     """exception used when the thinking cycles and doesn't seem to find an end"""
 
@@ -135,5 +138,5 @@
     """exception used when the thinking cycles and doesn't seem to find an end"""
 
-class BadAilRule(Exception):
+class BadAilRule(AilError):
     """exception used when a malformatted rule is parsed"""
 
@@ -138,6 +141,9 @@
     """exception used when a malformatted rule is parsed"""
 
-class AILBrainHandler:
+class BadAilCommand(AilError):
+    """exception used when an unknown command was used"""
+
+class AILBrainHandler(object):
     """a default command handler used to interactivly play with ail"""
     def command(self, cmdname, *args):
         return 'command : %s %s' % (cmdname, str(args))
@@ -162,8 +168,8 @@
             if encoding is not None:
                 string = unicode(string, encoding)
             return string
-        
-class Brain:
+
+class Brain(object):
     """the ail brain: process text according to loaded rules
     """
 
@@ -172,7 +178,7 @@
         self._cmds_hdlr = cmds_hdlr
         self.encoding = encoding
         self.source_files = []
-        
+
     def load(self, filenames, env_context = None):
         """load rules files"""
         for name in filenames:
@@ -187,7 +193,6 @@
         self.source_files = []
         self.load(filenames)
 
-    
     def load_stream(self, stream, base_dir='', env_context = None):
         """load rules from stream"""
         self._add_patterns(read_from_stream(stream, base_dir, env_context))
@@ -191,7 +196,7 @@
     def load_stream(self, stream, base_dir='', env_context = None):
         """load rules from stream"""
         self._add_patterns(read_from_stream(stream, base_dir, env_context))
-        
+
     def load_string(self, string, base_dir='', env_context = None):
         """load rules from string"""
         self._add_patterns(read_from_string(string, base_dir, env_context))
@@ -218,7 +223,7 @@
                     next = next % dict([(str(key), val) for key, val in enumerate(groups)])
                 return target, next
         raise NoRewriteError()
-    
+
     def think(self, input, encoding=None):
         """process the given input, returning the value produced by thinking
         (i.e. a direct answer or the result of a command)
@@ -238,7 +243,7 @@
             rule_type, next = self._rewrite(next)
 ##             except NoRewriteError :
 ##                 # FIXME (syt+adim): should not catch this exception, imo rewrite without
-##                 # ending command is a bug in the rule file 
+##                 # ending command is a bug in the rule file
 ##                 return next
 ##         if rule_type == 'TERMINAL':
         words = self.split(next)
@@ -242,7 +247,10 @@
 ##                 return next
 ##         if rule_type == 'TERMINAL':
         words = self.split(next)
-        method = getattr(self._cmds_hdlr, words[0].lower())
+        try:
+            method = getattr(self._cmds_hdlr, words[0].lower())
+        except AttributeError:
+            raise AilError('Unknown action %s' % words[0].lower())
         return method(*[type_cast(w, encoding) for w in words[1:]])
 
     def split(self, string):
@@ -259,5 +267,5 @@
                 continue
             if self.split(next)[:len(searching)] == searching:
                 yield rgx.pattern
-            
+
 
@@ -263,4 +271,4 @@
 
-        
+
 if __name__ == '__main__' :
     run(sys.argv[1:])