Comment 0 for bug 1369362

This error is raised for certain inputs to clean_html method in class Cleaner, when iterating over attributes dictionary in order to remove non-safe ones. See attached file for details and steps to reproduce.

lxml.etree: (3, 4, 0, 0)
libxml used: (2, 9, 1)
libxml compiled: (2, 9, 1)
libxslt used: (1, 1, 28)
libxslt compiled: (1, 1, 28)