+import re
+import cPickle as pickle
+
+
+class Visitor:
+
+ def __init__(self):
+ self.dispatch = {}
+ self.dispatch[type(None)] = self.visitNone
+ self.dispatch[bool] = self.visitBool
+ self.dispatch[int] = self.visitInt
+ self.dispatch[long] = self.visitInt
+ self.dispatch[float] = self.visitFloat
+ self.dispatch[str] = self.visitStr
+ self.dispatch[tuple] = self.visitTuple
+ self.dispatch[list] = self.visitList
+ self.dispatch[dict] = self.visitDict
+ self.dispatch[bytearray] = self.visitByteArray
+
+ def visit(self, obj, *args, **kwargs):
+ return self.dispatch[type(obj)](obj, *args, **kwargs)
+
+ def visitAtom(self, obj, *args, **kwargs):
+ raise NotImplementedError
+
+ def visitNone(self, obj, *args, **kwargs):
+ return self.visitAtom(obj, *args, **kwargs)
+
+ def visitBool(self, obj, *args, **kwargs):
+ return self.visitAtom(obj, *args, **kwargs)
+
+ def visitInt(self, obj, *args, **kwargs):
+ return self.visitAtom(obj, *args, **kwargs)
+
+ def visitFloat(self, obj, *args, **kwargs):
+ return self.visitAtom(obj, *args, **kwargs)
+
+ def visitStr(self, obj, *args, **kwargs):
+ return self.visitAtom(obj, *args, **kwargs)
+
+ def visitIterable(self, obj, *args, **kwargs):
+ raise NotImplementedError
+
+ def visitTuple(self, obj, *args, **kwargs):
+ return self.visitIterable(obj, *args, **kwargs)
+
+ def visitList(self, obj, *args, **kwargs):
+ return self.visitIterable(obj, *args, **kwargs)
+
+ def visitDict(self, obj, *args, **kwargs):
+ raise NotImplementedError
+
+ def visitByteArray(self, obj, *args, **kwargs):
+ raise NotImplementedError
+
+
+class Dumper(Visitor):
+
+ id_re = re.compile('^[_A-Za-z][_A-Za-z0-9]*$')
+
+ def visitAtom(self, obj, *args, **kwargs):
+ return repr(obj)
+
+ def visitStr(self, obj, *args, **kwargs):
+ if self.id_re.match(obj):
+ return obj
+ else:
+ return repr(obj)
+
+ def visitTuple(self, obj, *args, **kwargs):
+ return '[' + ', '.join(itertools.imap(self.visit, obj)) + ']'
+
+ def visitList(self, obj, *args, **kwargs):
+ return '(' + ', '.join(itertools.imap(self.visit, obj)) + ')'
+
+ def visitByteArray(self, obj, *args, **kwargs):
+ return 'blob(%u)' % len(obj)
+
+
+class Hasher(Visitor):
+ '''Returns a hashable version of the objtree.'''
+
+ def visitAtom(self, obj, *args, **kwargs):
+ return obj
+
+ def visitIterable(self, obj, *args, **kwargs):
+ return tuple(itertools.imap(self.visit, obj))
+
+ def visitByteArray(self, obj, *args, **kwargs):
+ return str(obj)