from email.parser import BytesParser, Parserfrom email.policy import defaultpayload = 'Content-Type:x;\x1b*="\'G\'\\"""""'msg = Parser(policy=default).parsestr(payload)print(msg.get('content-type'))When trying to review PR for BPO 37461, I found another bug where an IndexErroris raised if there aren't closing quote characters in the input message:Suggested patch:@@ -1191,7 +1192,7 @@ def get_bare_quoted_string(value):             "expected '\"' but found '{}'".format(value))     bare_quoted_string = BareQuotedString()     value = value[1:]-    if value[0] == '"':+    if value and value[0] == '"':         token, value = get_qcontent(value)         bare_quoted_string.append(token)     while value and value[0] != '"':

An Python exception is not a crash; a crash is the program stopping without an exception and proper cleanup.If s is a string (rather than, for instance, None),s and (s[0] == char) is equivalent to s[0:1] == char

Thanks for the explanation Terry!In this case, value becomes None (I think), which causes the IndexError.

To avoid such questions, bug reports should contain exception messages and usually at least some of the tracebacks.>>> ''[0]Traceback (most recent call last):  File "<pyshell#0>", line 1, in <module>    ''[0]IndexError: string index out of range>>> x=None>>> x[0]Traceback (most recent call last):  File "<pyshell#3>", line 1, in <module>    x[0]TypeError: 'NoneType' object is not subscriptableIndexError should mean object was indexable.Operations on None should give TypeError.

Also, quotes should be attributed to a file and patch snipped should indicate the target.  As for the bug, the author(s) of the expressions "value[1:]" and "value[0]" presumably *expected* value to initially have length 2 so that it would be be non-empty after clipping.  In the absence of additional information, it is possible that the bug is in the unquoted code that produced value.  This is potentially true whenever a function or expession raises.

I just wanted to report before I forgot and hence missed some details, turns out the bug report was slightly wrong too. The testcase I provided wasn't right.Here is the right test case to reproduce the exception with master:# bpo_37491.pyfrom email.parser import BytesParser, Parserfrom email.policy import defaultpayload = 'Content-Type:"'msg = Parser(policy=default).parsestr(payload)print(msg.get('content-type'))$ ./python bpo_37491.py                                                                                                                                                              Traceback (most recent call last):  File "bpo_37491.py", line 5, in <module>    msg = Parser(policy=default).parsestr(payload)  File "/home/maxking/Documents/cpython/Lib/email/parser.py", line 68, in parsestr    return self.parse(StringIO(text), headersonly=headersonly)  File "/home/maxking/Documents/cpython/Lib/email/parser.py", line 58, in parse    return feedparser.close()  File "/home/maxking/Documents/cpython/Lib/email/feedparser.py", line 187, in close    self._call_parse()  File "/home/maxking/Documents/cpython/Lib/email/feedparser.py", line 180, in _call_parse    self._parse()  File "/home/maxking/Documents/cpython/Lib/email/feedparser.py", line 256, in _parsegen    if self._cur.get_content_type() == 'message/delivery-status':  File "/home/maxking/Documents/cpython/Lib/email/message.py", line 578, in get_content_type    value = self.get('content-type', missing)  File "/home/maxking/Documents/cpython/Lib/email/message.py", line 471, in get    return self.policy.header_fetch_parse(k, v)  File "/home/maxking/Documents/cpython/Lib/email/policy.py", line 163, in header_fetch_parse    return self.header_factory(name, value)  File "/home/maxking/Documents/cpython/Lib/email/headerregistry.py", line 602, in __call__    return self[name](name, value)  File "/home/maxking/Documents/cpython/Lib/email/headerregistry.py", line 197, in __new__    cls.parse(value, kwds)  File "/home/maxking/Documents/cpython/Lib/email/headerregistry.py", line 447, in parse    kwds['decoded'] = str(parse_tree)  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 126, in __str__    return ''.join(str(x) for x in self)  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 126, in <genexpr>    return ''.join(str(x) for x in self)  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 796, in __str__    for name, value in self.params:  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 770, in params    value = param.param_value  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 679, in param_value    return token.stripped_value  File "/home/maxking/Documents/cpython/Lib/email/_header_value_parser.py", line 710, in stripped_value    token = self[0]IndexError: list index out of rangeThis time I attached a correct patch instead of copy-pasting only the diff :)About IndexError, I agree, it must be an empty string value and not a None value.

@barrythe 3 PR have been merged, do you think we could close this issue?Thank you