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email.utils.collapse_rfc2231_value raises AttributeError on non-3-tuples #145824
Description
Bug report
Bug description:
Issue
collapse_rfc2231_value raises AttributeError: 'tuple' object has no attribute 'startswith' when passed a tuple whose length is not 3. The guard if not isinstance(value, tuple) or len(value) != 3 is meant to handle this case, but falls through to unquote(value) which expects a string.
Reproducer
from email.utils import collapse_rfc2231_value
collapse_rfc2231_value(('a', 'b'))
# AttributeError: 'tuple' object has no attribute 'startswith'CPython versions tested on:
CPython main branch
Operating systems tested on:
No response
Activity
picnixz commentedon Mar 11, 2026
I don't think we should change the behavior here. First, it's not a crash but rather a GIGO case (garbage in, garbage out). The documentation says:
So returning the stringification of the tuple may not necessarily be correct. Instead, a TypeError should be raised if AttributeError is too cryptic IMO.
[-]email.utils.collapse_rfc2231_value crashes with AttributeError on non-3-tuples[/-][+]email.utils.collapse_rfc2231_value raises AttributeError on non-3-tuples[/+]stefanzetzsche commentedon Mar 11, 2026
Thanks for the feedback! I appreciate this is a minor issue. I agree that a TypeError would be better than the AttributeError here.
As for the documentation:
It currently leaves implicit/undefined the case when the value passed is a tuple, but not a 3-tuple. I'm assuming "not a tuple" already means "not a 3-tuple" given the context, but making it explicit wouldn't hurt.
I'll revise the PR accordingly.
picnixz commentedon Mar 11, 2026
Yeah, for me it was obvious that the "this" in "this into a unicode string" referred to "a 3-tuple" returned by the other function. I'd be more in favor of (1) having a TypeError (2) and a doc clarification if necessary.