[New-bugs-announce] [issue33524] non-ascii characters in headers causes TypeError on email.policy.Policy.fold

[radical164]

New submission from radical164 <tptlab at tuta.io>:

Python 3.6.5 has trouble on folding email messages:

Traceback (most recent call last):
  File "emailtest.py", line 7, in <module>
    policy.fold("Subject", msg["Subject"])
  File "/usr/lib/python3.6/email/policy.py", line 183, in fold
    return self._fold(name, value, refold_binary=True)
  File "/usr/lib/python3.6/email/policy.py", line 205, in _fold
    return value.fold(policy=self)
  File "/usr/lib/python3.6/email/headerregistry.py", line 258, in fold
    return header.fold(policy=policy)
  File "/usr/lib/python3.6/email/_header_value_parser.py", line 144, in fold
    return _refold_parse_tree(self, policy=policy)
  File "/usr/lib/python3.6/email/_header_value_parser.py", line 2651, in _refold_parse_tree
    part.ew_combine_allowed, charset)
  File "/usr/lib/python3.6/email/_header_value_parser.py", line 2728, in _fold_as_ew
    first_part = to_encode[:text_space]
TypeError: slice indices must be integers or None or have an __index__ method


The message has non-ascii characters in header and set max_line_length=0, regardless length of the header. Here is the code to reproduce.


from email.message import EmailMessage
from email.policy import default

policy = default.clone(max_line_length=0)
msg = EmailMessage()
msg["Subject"] = "á"
policy.fold("Subject", msg["Subject"])


I first found this issue on Maildir.add, which saves the message to a file without word wrap.

----------
components: email
messages: 316680
nosy: barry, r.david.murray, radical164
priority: normal
severity: normal
status: open
title: non-ascii characters in headers causes TypeError on email.policy.Policy.fold
type: behavior
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33524>
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