lxml tostring() returns blank string in Flask running on mod-wsgi

问题

I have a Python 2.7.6 Flask application that is trying to parse a SAML XML document using the lxml library. I'm running into an issue where etree.tostring(...) returns an empty string.

etree_string = etree.tostring(etree.fromstring(b'<test1><test2></test2></test1>'))
return etree_string
# output: ''

This appears to only occur when the code is run within the Flask app, served by mod_wsgi in Apache. I say this because in the same virtualenv, if I open a python interpreter and run:

>>> etree_string = etree.tostring(etree.fromstring(b'<test1><test2></test2></test1>'))
>>> print etree_string
<test1><test2/></test1>

Anyone have an idea on what might be going on?

来源：https://stackoverflow.com/questions/40599442/lxml-tostring-returns-blank-string-in-flask-running-on-mod-wsgi