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I can confirm that the crash from pasting these characters happens when trying to fetch the clipboard contents. We can override the built-in <<Paste>> event, but then we have to get the clipboard's contents directly, and the only portable way to do that in the stdlib is via Tkinter's clipboard_get(). (For a non-stdlib solution, check out pyperclip on PyPI.)
clipboard_get(), which I assume calls what Tk uses internally to handle the <<Paste>> event, crashes in the C code with a UnicodeDecodeError. Here's a traceback from calling clipboard_get() with 🐱 in the clipboard (Windows 10, recent master branch, i.e. to be 3.9):
Exception in Tkinter callback
Traceback (most recent call last):
 File "C:\Users\Tal\dev\cpython\lib\tkinter\__init__.py", line 1885, in __call__
 return self.func(*args)
 File "C:\Users\Tal\dev\cpython\lib\idlelib\multicall.py", line 176, in handler
 r = l[i](event)
 File "C:\Users\Tal\dev\cpython\lib\idlelib\editor.py", line 618, in paste
 print(self.text.clipboard_get())
 File "C:\Users\Tal\dev\cpython\lib\tkinter\__init__.py", line 867, in clipboard_get
 return self.tk.call(('clipboard', 'get') + self._options(kw))
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xed in position 0: invalid continuation byte
From a quick look, this appears to be happening in _tkinter.c, here:
static PyObject *
unicodeFromTclStringAndSize(const char *s, Py_ssize_t size)
{
 PyObject *r = PyUnicode_DecodeUTF8(s, size, NULL);
 ...
My guess is that Tk is passing the clipboard contents as-is, and we're simply not decoding it with the proper encoding (i.e. utf-16le on Windows).
Is this something worth fixing / working around in Tkinter, e.g. by using a proper encoding depending on the platform for fetching clipboard contents? Or are we content to continue waiting for Tk to fix this?