special formatting when probability = 1.0, cf issue nltk_book#37

nltk/grammar.py

@@ -398,7 +398,8 @@ class ProbabilisticProduction(Production, ImmutableProbabilisticMixIn):
         Production.__init__(self, lhs, rhs)
 
     def __str__(self):
-        return Production.__unicode__(self) + ' [%.6g]' % self.prob()
+        return Production.__unicode__(self) + \
+            (' [1.0]' if (self.prob() == 1.0) else ' [%.g]' % self.prob())
 
     def __eq__(self, other):
         return (type(self) == type(other) and