bpo-13153: Use OS native encoding for converting between Python and Tcl.

On Windows use UTF-16 (or UTF-32 for 32-bit Tcl_UniChar) with the
"surrogatepass" error handler for converting to/from Tcl Unicode objects.

On Linux use UTF-8 with the "surrogateescape" error handler for converting
to/from Tcl String objects.

Converting strings from Tcl to Python and back now never fails
(except MemoryError).

Lib/idlelib/pyshell.py

@@ -1298,16 +1298,6 @@ def resetoutput(self):
         self.set_line_and_column()
 
     def write(self, s, tags=()):
-        if isinstance(s, str) and len(s) and max(s) > '\uffff':
-            # Tk doesn't support outputting non-BMP characters
-            # Let's assume what printed string is not very long,
-            # find first non-BMP character and construct informative
-            # UnicodeEncodeError exception.
-            for start, char in enumerate(s):
-                if char > '\uffff':
-                    break
-            raise UnicodeEncodeError("UCS-2", char, start, start+1,
-                                     'Non-BMP character not supported in Tk')
         try:
             self.text.mark_gravity("iomark", "right")
             count = OutputWindow.write(self, s, tags, "iomark")

Lib/test/test_tcl.py

@@ -429,9 +429,12 @@ def passValue(value):
         self.assertEqual(passValue(False), False if self.wantobjects else '0')
         self.assertEqual(passValue('string'), 'string')
         self.assertEqual(passValue('string\u20ac'), 'string\u20ac')
+        self.assertEqual(passValue('string\U0001f4bb'), 'string\U0001f4bb')
         self.assertEqual(passValue('str\x00ing'), 'str\x00ing')
         self.assertEqual(passValue('str\x00ing\xbd'), 'str\x00ing\xbd')
         self.assertEqual(passValue('str\x00ing\u20ac'), 'str\x00ing\u20ac')
+        self.assertEqual(passValue('str\x00ing\U0001f4bb'),
+                         'str\x00ing\U0001f4bb')
         self.assertEqual(passValue(b'str\x00ing'),
                          b'str\x00ing' if self.wantobjects else 'str\x00ing')
         self.assertEqual(passValue(b'str\xc0\x80ing'),
@@ -490,6 +493,7 @@ def float_eq(actual, expected):
         check('string')
         check('string\xbd')
         check('string\u20ac')
+        check('string\U0001f4bb')
         check('')
         check(b'string', 'string')
         check(b'string\xe2\x82\xac', 'string\xe2\x82\xac')
@@ -531,6 +535,7 @@ def test_splitlist(self):
             ('a\n b\t\r c\n ', ('a', 'b', 'c')),
             (b'a\n b\t\r c\n ', ('a', 'b', 'c')),
             ('a \u20ac', ('a', '\u20ac')),
+            ('a \U0001f4bb', ('a', '\U0001f4bb')),
             (b'a \xe2\x82\xac', ('a', '\u20ac')),
             (b'a\xc0\x80b c\xc0\x80d', ('a\x00b', 'c\x00d')),
             ('a {b c}', ('a', 'b c')),

Misc/NEWS.d/next/Library/2019-09-29-22-47-37.bpo-13153.0mO9qR.rst

@@ -0,0 +1,4 @@
+OS native encoding is now used for converting between Python strings and
+Tcl objects.  This allows to display, copy and paste to clipboard emoji and
+other non-BMP characters.  Converting strings from Tcl to Python and back
+now never fails (except MemoryError).