bpo-34791: xml package obeys ignore env flags (GH-9544) (GH-9547)

The xml.sax and xml.dom.domreg modules now obey
sys.flags.ignore_environment.
Signed-off-by: Christian Heimes <christian@python.org>

https://bugs.python.org/issue34791
(cherry picked from commit 223e501f)
Co-authored-by: Christian Heimes <christian@python.org>

Lib/xml/dom/domreg.py

@@ -8,6 +8,8 @@ from xml.dom.minicompat import *  # isinstance, StringTypes
 # should be published by posting to xml-sig@python.org, and are
 # subsequently recorded in this file.
 
+import sys
+
 well_known_implementations = {
     'minidom':'xml.dom.minidom',
     '4DOM': 'xml.dom.DOMImplementation',
@@ -57,7 +59,7 @@ def getDOMImplementation(name = None, features = ()):
         return mod.getDOMImplementation()
     elif name:
         return registered[name]()
-    elif "PYTHON_DOM" in os.environ:
+    elif not sys.flags.ignore_environment and "PYTHON_DOM" in os.environ:
         return getDOMImplementation(name = os.environ["PYTHON_DOM"])
 
     # User did not specify a name, try implementations in arbitrary

Lib/xml/sax/__init__.py

@@ -59,7 +59,7 @@ if _false:
     import xml.sax.expatreader
 
 import os, sys
-if "PY_SAX_PARSER" in os.environ:
+if not sys.flags.ignore_environment and "PY_SAX_PARSER" in os.environ:
     default_parser_list = os.environ["PY_SAX_PARSER"].split(",")
 del os
 

Misc/NEWS.d/next/Security/2018-09-24-18-49-25.bpo-34791.78GmIG.rst

+The xml.sax and xml.dom.domreg no longer use environment variables to
+override parser implementations when sys.flags.ignore_environment is set by
+-E or -I arguments.