Hello, I am hoping for a little help. I have been playing with the python ast module and have run into an issue that I need a little push on. I would like to be able to change a specific element in a specific node in an ast then compile the resulting ast. Consider the simplified example below with its output. In this example I would like a way to change a specific addition operation. With the NodeTransformer I see how to change every addition operator but not how to change a specific one. I would like this to work on both the 2.6 and 3.1 branches. Ideally I would like to read a file, count the instances of an operation of interest and then use an index to make the changes.
I am probably missing something simple but I am lost right now. import ast class SwitchMinusPlus(ast.NodeTransformer): def visit_BinOp(self, node): node = self.generic_visit(node) if isinstance(node.op, ast.Add): node.op = ast.Sub() return node myfile = open('trivial.py').read() print myfile tree = compile(myfile, '<string>', 'exec', ast.PyCF_ONLY_AST) print ast.dump(tree, annotate_fields=False, include_attributes=False) node = SwitchMinusPlus().visit(ast.parse(myfile)) print ast.dump(node, annotate_fields=False, include_attributes=False) Which gives the following output: Note that this code changes the addition operator to an subtraction operator at the AST level for every instance. a = 8 b = 6 c = b + a d = c + a Module([Assign([Name('a', Store())], Num(8)), Assign([Name('b', Store ())], Num(6)), Assign([Name('c', Store())], BinOp(Name('b', Load()), Add(), Name('a', Load()))), Assign([Name('d', Store())], BinOp(Name('c', Load()), Add(), Name('a', Load())))]) Module([Assign([Name('a', Store())], Num(8)), Assign([Name('b', Store ())], Num(6)), Assign([Name('c', Store())], BinOp(Name('b', Load()), Sub(), Name('a', Load()))), Assign([Name('d', Store())], BinOp(Name('c', Load()), Sub(), Name('a', Load())))]) Thanks in advance, Thomas -- http://mail.python.org/mailman/listinfo/python-list