homepage

Attached patch deprecates invalid escape sequences in unicode strings. The point of this is to prevent issues such as #27356 (and possibly other similar ones) in the future.
Without the patch:
>>> "hello \world"
'hello \\world'
With the patch:
>>> "hello \world"
DeprecationWarning: invalid escape sequence 'w'
I'll need some help (patch isn't mergeable yet):
test_doctest fails on my machine with the patch (and -W), and I don't know how to fix it. test_ast fails an assertion (!PyErr_Occurred() in PyObject_Call in abstract.c) when -W is on, and I also don't know how to fix it (I don't even know what causes it).
Of course, I went ahead and fixed all instances of invalid escape sequences in the stdlib (that I could find) so that no DeprecationWarning is encountered.
Lastly, I thought about also doing this to bytes, but I ran into some issues with some invalid escapes such as \u, and _codecs.escape_decode would trigger the warning when passed br"8円" (for example). Ultimately, I decided to leave bytes alone for now, since it's mostly on the lower-level side of things. If there's interest I can add it back.