Paste #36482

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posted on 2008-03-30 13:18

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import ast


class GenshiSemantics(ast.NodeTransformer):

    def context(self, method):
        return ast.Expr(ast.Call(
            ast.Attribute(ast.Name('data', ast.Load()), method, ast.Load()),
            [], [], None, None
        ))

    def visit_For(self, node):
        self.generic_visit(node)
        return [self.context('push'), node, self.context('pop')]

    def visit_Name(self, node):
        self.generic_visit(node)
        return ast.Subscript(
            ast.Name('data', ast.Load()),
            ast.Index(ast.Str(node.id)),
            node.ctx
        )


class Context(object):

    def __init__(self):
        self.stack = [{}]

    def __getitem__(self, key):
        for item in reversed(self.stack):
            if key in item:
                return item[key]
        raise KeyError(key)

    def __setitem__(self, key, value):
        self.stack[-1][key] = value

    def push(self):
        self.stack.append({})

    def pop(self):
        self.stack.pop()


node = ast.parse('''
seq = [1, 2, 3, 4, 5]
item = 42
for item in seq:
    print 'inside', item
print 'outside', item
''')

node = ast.fix_missing_locations(GenshiSemantics().visit(node))

print 'Code in Python Source:'
print ast.to_source(node)

print
print 'Run it:'
code = compile(node, '<template>', 'exec')
namespace = {'data': Context()}
exec code in namespace