Re: ast manipulation
Terry, Thank you for responding. I actually figured out how to do this shortly after posting the message. Sorry I wasn't quite clear enough in my post, I will try to be a little more explict in the future. Just to mention it I want to go to each node in the ast including child nodes and change the values. I am making a limited mutation analysis program. If it looks generally useful as I get further along I will release the code. I did an early prototype that worked on the text of the code itself but I thought that using the ast for this would be better and maybe a little faster. Regards, Thomas -- http://mail.python.org/mailman/listinfo/python-list
ast manipulation
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
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Re: ast manipulation
Tsize wrote:
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.
If you can identify the specific nodes you want to change, no problem
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.
Which specific one or 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.
If 'specific one' means number i, great. In not, not.
I am probably missing something simple but I am lost right now.
You have not said what 'specific one' means.
Nor what your general goal is, why you want to change asts.
import ast
class SwitchMinusPlus(ast.NodeTransformer):
def visit_BinOp(self, node):
node = self.generic_visit(node)
if isinstance(node.op, ast.Add):
if isinstance(node.op, ast.Add) and isspecificnode(node):
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(])
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