compiler.walk() what am I missing?

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Here's a trivial little Python session which attempts to use compiler.walk
(mostly unsuccessfully):

% python
Python 2.4.2 (#1, Feb 23 2006, 12:48:31)
[GCC 3.4.1] on sunos5
Type "help", "copyright", "credits" or "license" for more information.

>>import compiler
ast = compiler.parse(open("a.py").read())
ast

Module(None, Stmt([Assign([AssName('RED', 'OP_ASSIGN')], Const('red')), Assign([AssName('BLUE', 'OP_ASSIGN')], Const('blue'))]))

>>compiler.walk(ast, compiler.visitor.ExampleASTVisitor, verbose=10)
<class compiler.visitor.ExampleASTVisitor at 0x831ce3c>
compiler.walk(ast, compiler.visitor.ExampleASTVisitor(), verbose=10)

<compiler.visitor.ExampleASTVisitor instance at 0x81f0eac>

I did manage to get a verbose print the first time I executed this:

>>compiler.walk(ast, compiler.visitor.ExampleASTVisitor(), walker=compiler.visitor.ExampleASTVisitor(), verbose=10)

which emitted nice verbose stuff like

dispatch Module

<compiler.visitor.ExampleASTVisitor instance at 0x835074c>
compiler.ast.Module
asList <bound method Module.asList of Module(None, Stmt([Assign([AssName('RED', 'OP_ASSIGN')], Const('red')), Assign([AssName('BLUE', 'OP_ASSIGN')], Const('blue'))]))>
doc None
getChildNode <bound method Module.getChildNodes of Module(None, Stmt([Assign([AssName('RED', 'OP_ASSIGN')], Const('red')), Assign([AssName('BLUE', 'OP_ASSIGN')], Const('blue'))]))>
getChildren <bound method Module.getChildren of Module(None, Stmt([Assign([AssName('RED', 'OP_ASSIGN')], Const('red')), Assign([AssName('BLUE', 'OP_ASSIGN')], Const('blue'))]))>
lineno None
...

but successive calls just yielded the more electron-conserving:

dispatch Module
dispatch Stmt
dispatch Assign
dispatch AssName
dispatch Const
dispatch Assign
dispatch AssName
dispatch Const

What am I doing wrong?

Thanks,

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