Great! Thanks Dino.
With the following C# code:
using System;
using System.Collections;
using System.Collections.Generic;
using IronPython.Compiler.Ast;
using Microsoft.Scripting;
namespace ExpressionWalker
{
public class ExpressionWalker : PythonWalker
{
public List<string> names = new List<string>();
public override bool Walk(NameExpression node)
{
names.Add(SymbolTable.IdToString(node.Name));
return true; // means walk this node, not important for a
Name node.
}
}
}
The following Python code:
import clr
clr.AddReference('ExpressionWalker')
clr.AddReference('IronPython')
clr.AddReference('Microsoft.Scripting')
from IronPython import PythonEngineOptions
from IronPython.Hosting import PythonEngine
from IronPython.Compiler import Parser
from Microsoft.Scripting import CompilerContext, SourceCodeUnit
from ExpressionWalker import ExpressionWalker
expression = "A1 * 3 + B4"
pe = PythonEngine.CurrentEngine
s = SourceCodeUnit(pe, expression)
c = CompilerContext(s)
p = Parser.CreateParser(c, PythonEngineOptions())
e = p.ParseExpression()
w = ExpressionWalker()
e.Walk(w)
print list(w.names)
Produces:
['A1', 'B4']
This works in Silverlight (which is my intention). :-)
I'll add this to the cookbook, but I realise that parts of this
interface may be unstable...
Michael
Dino Viehland wrote:
> PythonWalker and MS.Ast.Walker are actually different - PythonWalker walks
> the IronPython AST before its transformed to a DLR AST, and MS.Ast.Walker
> walks the DLR AST.
>
> You can certainly party on the Expression object all you want. But it'd be
> much easier (and less prone to break as we make changes to the AST) to create
> a subclass of PythonWalker. This is really easy in C# because it's just:
>
> class MyWalker : PythonWalker {
> public override bool Walk(NameExpression node) {
> Console.WriteLine(SymbolTable.IdToString(node.Name));
> return true; // means walk this node, not important for a
> Name node.
> }
> }
>
> Then:
> e = p.ParseExpression()
> e.Walk(MyWalker())
>
> >From Python it's a little more tricky because all the Walk nodes are
> >overloaded - and by a little more tricky I mean you just need to test the
> >type of node coming in :).
> (I haven't actually compiled any of this, but that's the theory).
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Foord
> Sent: Monday, August 13, 2007 5:06 PM
> To: Discussion of IronPython
> Subject: Re: [IronPython] Dear Lazy Web - IronPython 2 Parser
>
> Thanks for the reply Dino.
>
> Leaving some kind of API exposed to the Python parser would be
> appreciated, rather than making it private.
>
> What I would like to do in this case, is discover what variable names a
> Python expression uses.
>
> I know how to do this for a Python AST (name nodes that are the first
> child of an atom node). I don't even need to modify the AST - I just
> want to pull the names out.
>
> From what you said, I *think* that using Parser.CreateParser sounds the
> closest.
>
> With the help you provided, I got as far as the following code:
>
> import clr
> clr.AddReference('IronPython')
> clr.AddReference('Microsoft.Scripting')
>
> from IronPython import PythonEngineOptions
> from IronPython.Hosting import PythonEngine
> from IronPython.Compiler import Parser
> from Microsoft.Scripting import CompilerContext, SourceCodeUnit
>
> expression = "3 * 3"
> pe = PythonEngine.CurrentEngine
>
> s = SourceCodeUnit(pe, expression)
> c = CompilerContext(s)
> p = Parser.CreateParser(c, PythonEngineOptions())
>
> e = p.ParseExpression()
>
> This gets me a BinaryExpression object, which has interesting properties
> like 'Left', 'Right', 'Start' and 'End' and a Walk method that takes a
> PythonWalker. (Presumably BinaryExpression is a node type - the root
> node of this particular expression.)
>
> I can find Microsoft.Scripting.Ast.Walker (which has multiple overloads
> of Walk for different node types). I assume the PythonWalker is a
> subclass of this.
>
> Can I use the expression object to inspect its nodes without creating a
> walker?
>
> Thanks for the help. :-)
>
> Michael
>
> Dino Viehland wrote:
>
>> I don't know if you figured this out yet but here goes...
>>
>> Our Parser class is still public (I'm not sure if this will change or not)
>> but you can do (IronPython.Compiler.)Parser.CreateParser. That takes a
>> CompilerContext class which is going to point the parser at a SourceUnit
>> that we are currently parsing.
>>
>> >From there you can call ParseFileInput and it'll parse the file and return
>> >you the IronPython AST. The interesting part might be if you actually want
>> >to compile that code later on :). In that case you might want to look at
>> >PythonScriptCompiler to see the rest of the process - it's really just one
>> >call to PythonScriptCompiler.BindAndTransform which also seems to be public
>> >(again, I'm not sure if that'll change or not).
>>
>> Alternately if you just want a way to paramterize some user code you might
>> want to look at ScriptCompiler.ParseCodeDom. This allows you to provide a
>> limited CodeDom tree (we support CodeMemberMethod, and snippet statement /
>> expressions and that's it) which you could create from some user input. The
>> nice thing about that is it won't be Python specific (although I'm guessing
>> that's not a problem for you :) ).
>>
>>
>> -----Original Message-----
>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Foord
>> Sent: Wednesday, August 08, 2007 3:50 PM
>> To: Discussion of IronPython
>> Subject: [IronPython] Dear Lazy Web - IronPython 2 Parser
>>
>> Hello all,
>>
>> Sorry for being lazy, but...
>>
>> What is the easiest way of building an AST from IronPython 2 code? I
>> would like an AST that I can modify and then flatten again in
>> Silverlight.... It needn't be a Python AST, an IronPython one is fine. I
>> only need access to 'name' nodes... I wish to change some of the names
>> and turn the AST back into code before exec'ing.
>>
>> :-)
>>
>> Thanks
>>
>>
>> Michael
>> http://www.ironpython.info/
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>>
>>
>>
>
>
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