Just to reiterate this point, lxml.etree supports a "pretty_print" flag in its tostring() function and ElementTree.write(). It would thus make sense to support the same thing in ET.

http://lxml.de/api.html#serialisation

For completeness, the current signature looks like this:

def tostring(element_or_tree, *, encoding=None, method="xml",
             xml_declaration=None, pretty_print=False,
             with_tail=True, standalone=None, doctype=None,
             exclusive=False, with_comments=True,
             inclusive_ns_prefixes=None):

(The last three options are for C14N serialisation.)