只是两个问题：
例如：
from lxml import etree
from StringIO import StringIO
tree = etree.parse(StringIO('<foo><bar></bar></foo>'))
try:
tree.xpath('\BAD XPATH')
print '1. Valid XPath'
except etree.XPathEvalError, e:
print '1. Invalid XPath: ', e
if not tree.xpath('/foo/xxx'):
print '2. Requested node does not exist.'
运行如下：
1. Invalid XPath: Invalid expression
2. Requested node does not exist.
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我来说两句