Eliminar atributos de namespace python de um lxml.objectify.ObjectifiedElement [duplicate]

Possible Duplicate:
Ao usar lxml, o XML pode ser renderizado sem atributos de espaço para nom

Como retirar os atributos python de umlxml.objectify.ObjectifiedElement?

Exemplo

In [1]: from lxml import etree, objectify
In [2]: foo = objectify.Element("foo")
In [3]: foo.bar = "hi"
In [4]: foo.baz = 1
In [5]: foo.fritz = None
In [6]: print etree.tostring(foo, pretty_print=True)
<foo xmlns:py="http://codespeak.net/lxml/objectify/pytype" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" py:pytype="TREE">
  <bar py:pytype="str">hi</bar>
  <baz py:pytype="int">1</baz>
  <fritz xsi:nil="true"/>
</foo>

Em vez disso, gostaria que a saída se parecesse com:

<foo>
  <bar>hi</bar>
  <baz>1</baz>
  <fritz/>
</foo>

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