[3.12] gh-115398: Expose Expat >=2.6.0 reparse deferral API (CVE-2023-52425) (GH-115623) by hartwork · Pull Request #116248

[3.12] gh-115398: Expose Expat >=2.6.0 reparse deferral API (CVE-2023-52425) (GH-115623) by hartwork · Pull Request #116248 · python/cpython

…52425) (pythonGH-115623)

Allow controlling Expat >=2.6.0 reparse deferral (CVE-2023-52425) by adding five new methods:

- `xml.etree.ElementTree.XMLParser.flush`
- `xml.etree.ElementTree.XMLPullParser.flush`
- `xml.parsers.expat.xmlparser.GetReparseDeferralEnabled`
- `xml.parsers.expat.xmlparser.SetReparseDeferralEnabled`
- `xml.sax.expatreader.ExpatParser.flush`

Based on the "flush" idea from python#115138 (comment) .

- Please treat as a security fix related to CVE-2023-52425.

Includes code suggested-by: Snild Dolkow <snild@sony.com>
and by core dev Serhiy Storchaka.

(cherry picked from commit 6a95676)

As suggested by Serhiy Storchaka

…t API availability (pythonGH-116278)

Suggest use of "hasattr" with checking for 3.13 Expat API availability

(cherry picked from commit 73807eb)

(cherry picked from commit eda2963)