SF patch# 1757839 by Alexandre Vassalotti -- make test_mailbox and
test_old_mailbox pass.
diff --git a/Lib/email/header.py b/Lib/email/header.py
index 675b68d..5ea1871 100644
--- a/Lib/email/header.py
+++ b/Lib/email/header.py
@@ -253,7 +253,7 @@
# We need to test that the string can be converted to unicode and
# back to a byte string, given the input and output codecs of the
# charset.
- if isinstance(s, str):
+ if isinstance(s, bytes):
# Possibly raise UnicodeError if the byte string can't be
# converted to a unicode with the input codec of the charset.
incodec = charset.input_codec or 'us-ascii'
@@ -263,7 +263,7 @@
# than the iput coded. Still, use the original byte string.
outcodec = charset.output_codec or 'us-ascii'
ustr.encode(outcodec, errors)
- elif isinstance(s, str):
+ elif isinstance(s, bytes):
# Now we have to be sure the unicode string can be converted
# to a byte string with a reasonable output codec. We want to
# use the byte string in the chunk.