In xml.etree, ElementTree and cElementTree implement different interfaces for the iterparse function/class.

In ElementTree, the argument "events" must be a tuple of strings:

from xml.etree import ElementTree as ET
for result in ET.iterparse('example.xml', events=('start', 'end')):
    print(result)

That works, given a valid XML file 'example.xml'. If the event names are given as bytes instead of strings (b'start', b'end'), there's no crash, but no events are recognized.

In cElementTree, it's the opposite: the events argument must be a tuple of bytes:

from xml.etree import cElementTree as cET
for result in cET.iterparse('example.xml', events=(b'start', b'end')):
    print(result)

Giving a tuple of strings instead of bytes results in:

>>> for result in cET.iterparse('example.xml', events=('start', 'end')):
...     print(result)
TypeError: invalid event tuple


This makes it difficult to use ElementTree as a backup for cElementTree, or at least very awkward.