Reported by Serhiy in issue 16564: >>> import io, email >>> bytesdata = b'\xfa\xfb\xfc\xfd\xfe\xff' >>> msg = email.mime.application.MIMEApplication(bytesdata, _encoder=encoders.encode_7or8bit) >>> s = io.BytesIO() >>> g = email.generator.BytesGenerator(s) >>> g.flatten(msg) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/serhiy/py/cpython3.2/Lib/email/generator.py", line 91, in flatten self._write(msg) File "/home/serhiy/py/cpython3.2/Lib/email/generator.py", line 137, in _write self._dispatch(msg) File "/home/serhiy/py/cpython3.2/Lib/email/generator.py", line 163, in _dispatch meth(msg) File "/home/serhiy/py/cpython3.2/Lib/email/generator.py", line 393, in _handle_text if _has_surrogates(msg._payload): TypeError: can't use a string pattern on a bytes-like object

New changeset f83581135ec4 by R David Murray in branch '3.2': #17171: fix email.encoders.encode_7or8bit when applied to binary data. http://hg.python.org/cpython/rev/f83581135ec4 New changeset cabcddbed377 by R David Murray in branch '3.3': Merge: #17171: fix email.encoders.encode_7or8bit when applied to binary data. http://hg.python.org/cpython/rev/cabcddbed377 New changeset a80b67611c6d by R David Murray in branch 'default': Merge: #17171: fix email.encoders.encode_7or8bit when applied to binary data. http://hg.python.org/cpython/rev/a80b67611c6d New changeset e44fa71d76fe by R David Murray in branch '2.7': #17171: backport behavior-confirming test from python3. http://hg.python.org/cpython/rev/e44fa71d76fe

Since this was straightforwardly similar to the issue 16564 fix I didn't bother with a review. The 2.7 commit is backporting the behavior-confirming test, just for thoroughness.