python/safeeval.py

   1
   2 ## http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/364469
   3 import compiler
   4
   5 class Unsafe_Source_Error(Exception):
   6     def __init__(self,error,descr = None,node = None):
   7         self.error = error
   8         self.descr = descr
   9         self.node = node
  10         self.lineno = getattr(node,"lineno",None)
  11
  12     def __repr__(self):
  13         return "Line %d.  %s: %s" % (self.lineno, self.error, self.descr)
  14     __str__ = __repr__
  15
  16 class SafeEval(object):
  17
  18     def visit(self, node,**kw):
  19         cls = node.__class__
  20         meth = getattr(self,'visit'+cls.__name__,self.default)
  21         return meth(node, **kw)
  22
  23     def default(self, node, **kw):
  24         for child in node.getChildNodes():
  25             return self.visit(child, **kw)
  26
  27     visitExpression = default
  28
  29     def visitConst(self, node, **kw):
  30         return node.value
  31
  32     def visitDict(self,node,**kw):
  33         return dict([(self.visit(k),self.visit(v)) for k,v in node.items])
  34
  35     def visitTuple(self,node, **kw):
  36         return tuple(self.visit(i) for i in node.nodes)
  37
  38     def visitList(self,node, **kw):
  39         return [self.visit(i) for i in node.nodes]
  40
  41     def visitUnarySub(self, node, **kw):
  42         return - self.visit (node.getChildNodes ()[0])
  43
  44 class SafeEvalWithErrors(SafeEval):
  45
  46     def default(self, node, **kw):
  47         raise Unsafe_Source_Error("Unsupported source construct",
  48                                 node.__class__,node)
  49
  50     def visitName(self,node, **kw):
  51         raise Unsafe_Source_Error("Strings must be quoted",
  52                                  node.name, node)
  53
  54     # Add more specific errors if desired
  55
  56
  57 def safe_eval(source, fail_on_error = True):
  58     walker = fail_on_error and SafeEvalWithErrors() or SafeEval()
  59     try:
  60         ast = compiler.parse(source,"eval")
  61     except SyntaxError, err:
  62         raise
  63     try:
  64         return walker.visit(ast)
  65     except Unsafe_Source_Error, err:
  66         raise
  67
  68
  69 def safe_eval(source, fail_on_error = True):
  70     walker = fail_on_error and SafeEvalWithErrors() or SafeEval()
  71     try:
  72         ast = compiler.parse(source,"eval")
  73     except SyntaxError, err:
  74         raise
  75     try:
  76         return walker.visit(ast)
  77     except Unsafe_Source_Error, err:
  78         raise
  79
  80 def test ():
  81     print safe_eval ('{1: [2,3], "4": (-1,2)}')
  82
  83 if __name__ == '__main__':
  84     test ()