#14731: refactor email policy framework.

This patch primarily does two things: (1) it adds some internal-interface
methods to Policy that allow for Policy to control the parsing and folding of
headers in such a way that we can construct a backward compatibility policy
that is 100% compatible with the 3.2 API, while allowing a new policy to
implement the email6 API.  (2) it adds that backward compatibility policy and
refactors the test suite so that the only differences between the 3.2
test_email.py file and the 3.3 test_email.py file is some small changes in
test framework and the addition of tests for bugs fixed that apply to the 3.2
API.

There are some additional teaks, such as moving just the code needed for the
compatibility policy into _policybase, so that the library code can import
only _policybase.  That way the new code that will be added for email6
will only get imported when a non-compatibility policy is imported.

1 files changed, 2 insertions, 2 deletions

diff --git a/Lib/email/parser.py b/Lib/email/parser.py
index 0f92160..1aab012 100644
--- a/Lib/email/parser.py
+++ b/Lib/email/parser.py
@@ -11,12 +11,12 @@ from io import StringIO, TextIOWrapper
 
 from email.feedparser import FeedParser
 from email.message import Message
-from email import policy
+from email._policybase import compat32
 
 
 
 class Parser:
-    def __init__(self, _class=Message, *, policy=policy.default):
+    def __init__(self, _class=Message, *, policy=compat32):
         """Parser of RFC 2822 and MIME email messages.
 
         Creates an in-memory object tree representing the email message, which