使用BeautifulSoup更改元素值将返回空元素

from BeautifulSoup import BeautifulStoneSoup

xml_data = """
<doc>
  <test>test</test>
  <foo:bar>Hello world!</foo:bar>
</doc>
"""

soup = BeautifulStoneSoup(xml_data)
print soup.prettify()
make = soup.find('foo:bar')
print make
# prints <foo:bar>Hello world!</foo:bar>

make.contents = ['Top of the world Ma!']
print make
# prints <foo:bar></foo:bar>
from BeautifulSoup import BeautifulStoneSoup

x