gh-115154: Fix untokenize handling of unicode named literals (#115171)

Lib/test/test_tokenize.py

@@ -1877,6 +1877,43 @@ class TestRoundtrip(TestCase):
                              "    print('Can not import' # comment2\n)"
                              "else:   print('Loaded')\n")
 
+        self.check_roundtrip("f'\\N{EXCLAMATION MARK}'")
+        self.check_roundtrip(r"f'\\N{SNAKE}'")
+        self.check_roundtrip(r"f'\\N{{SNAKE}}'")
+        self.check_roundtrip(r"f'\N{SNAKE}'")
+        self.check_roundtrip(r"f'\\\N{SNAKE}'")
+        self.check_roundtrip(r"f'\\\\\N{SNAKE}'")
+        self.check_roundtrip(r"f'\\\\\\\N{SNAKE}'")
+
+        self.check_roundtrip(r"f'\\N{1}'")
+        self.check_roundtrip(r"f'\\\\N{2}'")
+        self.check_roundtrip(r"f'\\\\\\N{3}'")
+        self.check_roundtrip(r"f'\\\\\\\\N{4}'")
+
+        self.check_roundtrip(r"f'\\N{{'")
+        self.check_roundtrip(r"f'\\\\N{{'")
+        self.check_roundtrip(r"f'\\\\\\N{{'")
+        self.check_roundtrip(r"f'\\\\\\\\N{{'")
+        cases = [
+    """
+if 1:
+    "foo"
+"bar"
+""",
+    """
+if 1:
+    ("foo"
+     "bar")
+""",
+    """
+if 1:
+    "foo"
+    "bar"
+""" ]
+        for case in cases:
+            self.check_roundtrip(case)
+
+
     def test_continuation(self):
         # Balancing continuation
         self.check_roundtrip("a = (3,4, \n"
@@ -1911,9 +1948,6 @@ class TestRoundtrip(TestCase):
         tempdir = os.path.dirname(__file__) or os.curdir
         testfiles = glob.glob(os.path.join(glob.escape(tempdir), "test*.py"))
 
-        # TODO: Remove this once we can untokenize PEP 701 syntax
-        testfiles.remove(os.path.join(tempdir, "test_fstring.py"))
-
         if not support.is_resource_enabled("cpu"):
             testfiles = random.sample(testfiles, 10)
 

Lib/tokenize.py

@@ -168,6 +168,7 @@ class Untokenizer:
         self.tokens = []
         self.prev_row = 1
         self.prev_col = 0
+        self.prev_type = None
         self.encoding = None
 
     def add_whitespace(self, start):
@@ -183,6 +184,29 @@ class Untokenizer:
         if col_offset:
             self.tokens.append(" " * col_offset)
 
+    def escape_brackets(self, token):
+        characters = []
+        consume_until_next_bracket = False
+        for character in token:
+            if character == "}":
+                if consume_until_next_bracket:
+                    consume_until_next_bracket = False
+                else:
+                    characters.append(character)
+            if character == "{":
+                n_backslashes = sum(
+                    1 for char in _itertools.takewhile(
+                        "\\".__eq__,
+                        characters[-2::-1]
+                    )
+                )
+                if n_backslashes % 2 == 0:
+                    characters.append(character)
+                else:
+                    consume_until_next_bracket = True
+            characters.append(character)
+        return "".join(characters)
+
     def untokenize(self, iterable):
         it = iter(iterable)
         indents = []
@@ -214,11 +238,13 @@ class Untokenizer:
                 startline = False
             elif tok_type == FSTRING_MIDDLE:
                 if '{' in token or '}' in token:
+                    token = self.escape_brackets(token)
+                    last_line = token.splitlines()[-1]
                     end_line, end_col = end
-                    end = (end_line, end_col + token.count('{') + token.count('}'))
-                    token = re.sub('{', '{{', token)
-                    token = re.sub('}', '}}', token)
-
+                    extra_chars = last_line.count("{{") + last_line.count("}}")
+                    end = (end_line, end_col + extra_chars)
+            elif tok_type in (STRING, FSTRING_START) and self.prev_type in (STRING, FSTRING_END):
+                self.tokens.append(" ")
 
             self.add_whitespace(start)
             self.tokens.append(token)
@@ -226,6 +252,7 @@ class Untokenizer:
             if tok_type in (NEWLINE, NL):
                 self.prev_row += 1
                 self.prev_col = 0
+            self.prev_type = tok_type
         return "".join(self.tokens)
 
     def compat(self, token, iterable):
@@ -233,6 +260,7 @@ class Untokenizer:
         toks_append = self.tokens.append
         startline = token[0] in (NEWLINE, NL)
         prevstring = False
+        in_fstring = 0
 
         for tok in _itertools.chain([token], iterable):
             toknum, tokval = tok[:2]
@@ -251,6 +279,10 @@ class Untokenizer:
             else:
                 prevstring = False
 
+            if toknum == FSTRING_START:
+                in_fstring += 1
+            elif toknum == FSTRING_END:
+                in_fstring -= 1
             if toknum == INDENT:
                 indents.append(tokval)
                 continue
@@ -263,11 +295,18 @@ class Untokenizer:
                 toks_append(indents[-1])
                 startline = False
             elif toknum == FSTRING_MIDDLE:
-                if '{' in tokval or '}' in tokval:
-                    tokval = re.sub('{', '{{', tokval)
-                    tokval = re.sub('}', '}}', tokval)
+                tokval = self.escape_brackets(tokval)
+
+            # Insert a space between two consecutive brackets if we are in an f-string
+            if tokval in {"{", "}"} and self.tokens and self.tokens[-1] == tokval and in_fstring:
+                tokval = ' ' + tokval
+
+            # Insert a space between two consecutive f-strings
+            if toknum in (STRING, FSTRING_START) and self.prev_type in (STRING, FSTRING_END):
+                self.tokens.append(" ")
 
             toks_append(tokval)
+            self.prev_type = toknum
 
 
 def untokenize(iterable):

Misc/NEWS.d/next/Core and Builtins/2024-02-08-16-01-18.gh-issue-115154.ji96FV.rst

@@ -0,0 +1,2 @@
+Fix a bug that was causing the :func:`tokenize.untokenize` function to
+handle unicode named literals incorrectly. Patch by Pablo Galindo