Proposed patch removes old-deprecated ElementTree features.

* Methods Element.getchildren(), Element.getiterator() and ElementTree.getiterator() deprecated in 2.7 and 3.2.
 Use list(elem) or iteration instead of getchildren(), methods iter() instead of getiterator(). 

* The html argument of XMLParser deprecated in 3.4.
 The rest of arguments are keyword-only now (passing them as keywords was recommended in the documentatin).

* The support of the doctype() method of XMLParser subclasses and its default implementation. Deprecated in 3.2. Define the doctype() method on a custom TreeBuilder target instead.

* The xml.etree.cElementTree module deprecated in 3.3.

Unfortunately some of these deprecations are in the documentation only or in Python implementatation, but not in C implementatation. Perhaps missed warnings should be added first (see issue29204). But if commit the patch from issue29204 in 3.6, perhaps deprecated features could be removed in 3.7.

Patch looks right to me.

I'd personally be ok with applying it to 3.7, but I'll leave the decision to you. Most of the removed "features" are non-controversial, except:

- "getchildren()" is probably still in use, also because it's more efficient than "list(elem)" in lxml (and has never been deprecated there), so code that supports both libraries might have preferred it

- cElementTree is probably still imported by quite a bit of code

So, this will have an impact on user code, despite any previous deprecation warnings. But it's easy to resolve in a backwards compatible way.

Serhiy,

Did you want to revive this for 3.8?

getchildren() and getiterator() have deprecation notes in their docstrings in lxml.etree.

PR 6769 removes the html parameter and the doctype() method. getchildren() and getiterator() emit now a DeprecationWarning instead of PendingDeprecationWarning and will be removed in 3.9.

The following two patches will remove getchildren() and getiterator() (in 3.9) and xml.etree.cElementTree (in an unspecified future).

New changeset 02ec92fa7b1dddc23d479ee0b87dc283793505a8 by Serhiy Storchaka in branch 'master':
bpo-29209: Remove old-deprecated features in ElementTree. (GH-6769)
https://github.com/python/cpython/commit/02ec92fa7b1dddc23d479ee0b87dc283793505a8

This should be closed.

The rest will be removed in issue36543.