import compiler
class Unsafe_Source_Error(Exception):
def __init__(self,error,descr = None,node = None):
self.error = error
self.descr = descr
self.node = node
self.lineno = getattr(node,"lineno",None)
def __repr__(self):
return "Line %d. %s: %s" % (self.lineno, self.error, self.descr)
__str__ = __repr__
class SafeEval(object):
def visit(self, node,**kw):
cls = node.__class__
meth = getattr(self,'visit'+cls.__name__,self.default)
return meth(node, **kw)
def default(self, node, **kw):
for child in node.getChildNodes():
return self.visit(child, **kw)
visitExpression = default
def visitConst(self, node, **kw):
return node.value
def visitDict(self,node,**kw):
return dict([(self.visit(k),self.visit(v)) for k,v in node.items])
def visitTuple(self,node, **kw):
return tuple(self.visit(i) for i in node.nodes)
def visitList(self,node, **kw):
return [self.visit(i) for i in node.nodes]
class SafeEvalWithErrors(SafeEval):
def default(self, node, **kw):
raise Unsafe_Source_Error("Unsupported source construct",
node.__class__,node)
def visitName(self,node, **kw):
raise Unsafe_Source_Error("Strings must be quoted",
node.name, node)
# Add more specific errors if desired
def safe_eval(source, fail_on_error = True):
walker = fail_on_error and SafeEvalWithErrors() or SafeEval()
try:
ast = compiler.parse(source,"eval")
except SyntaxError, err:
raise
try:
return walker.visit(ast)
except Unsafe_Source_Error, err:
raise
