#24277: The new email API is no longer provisional.

This is a wholesale reorganization and editing of the email documentation to
make the new API the standard one, and the old API the 'legacy' one.  The
default is still the compat32 policy, for backward compatibility.  We will
change that eventually.

Doc/includes/email-read-alternative.py

@@ -0,0 +1,75 @@
+import os
+import sys
+import tempfile
+import mimetypes
+import webbrowser
+
+# Import the email modules we'll need
+from email import policy
+from email.parser import BytesParser
+
+# An imaginary module that would make this work and be safe.
+from imaginary import magic_html_parser
+
+# In a real program you'd get the filename from the arguments.
+with open('outgoing.msg', 'rb') as fp:
+    msg = BytesParser(policy=policy.default).parse(fp)
+
+# Now the header items can be accessed as a dictionary, and any non-ASCII will
+# be converted to unicode:
+print('To:', msg['to'])
+print('From:', msg['from'])
+print('Subject:', msg['subject'])
+
+# If we want to print a priview of the message content, we can extract whatever
+# the least formatted payload is and print the first three lines.  Of course,
+# if the message has no plain text part printing the first three lines of html
+# is probably useless, but this is just a conceptual example.
+simplest = msg.get_body(preferencelist=('plain', 'html'))
+print()
+print(''.join(simplest.get_content().splitlines(keepends=True)[:3]))
+
+ans = input("View full message?")
+if ans.lower()[0] == 'n':
+    sys.exit()
+
+# We can extract the richest alternative in order to display it:
+richest = msg.get_body()
+partfiles = {}
+if richest['content-type'].maintype == 'text':
+    if richest['content-type'].subtype == 'plain':
+        for line in richest.get_content().splitlines():
+            print(line)
+        sys.exit()
+    elif richest['content-type'].subtype == 'html':
+        body = richest
+    else:
+        print("Don't know how to display {}".format(richest.get_content_type()))
+        sys.exit()
+elif richest['content-type'].content_type == 'multipart/related':
+    body = richest.get_body(preferencelist=('html'))
+    for part in richest.iter_attachments():
+        fn = part.get_filename()
+        if fn:
+            extension = os.path.splitext(part.get_filename())[1]
+        else:
+            extension = mimetypes.guess_extension(part.get_content_type())
+        with tempfile.NamedTemporaryFile(suffix=extension, delete=False) as f:
+            f.write(part.get_content())
+            # again strip the <> to go from email form of cid to html form.
+            partfiles[part['content-id'][1:-1]] = f.name
+else:
+    print("Don't know how to display {}".format(richest.get_content_type()))
+    sys.exit()
+with tempfile.NamedTemporaryFile(mode='w', delete=False) as f:
+    # The magic_html_parser has to rewrite the href="cid:...." attributes to
+    # point to the filenames in partfiles.  It also has to do a safety-sanitize
+    # of the html.  It could be written using html.parser.
+    f.write(magic_html_parser(body.get_content(), partfiles))
+webbrowser.open(f.name)
+os.remove(f.name)
+for fn in partfiles.values():
+    os.remove(fn)
+
+# Of course, there are lots of email messages that could break this simple
+# minded program, but it will handle the most common ones.