Fix f-string replacement braces following backslashes

AUTHORS.txt

@@ -56,4 +56,6 @@ Batuhan Taskaya (@isidentical) <isidentical@gmail.com>
 Jocelyn Boullier (@Kazy) <jocelyn@boullier.bzh>
 
 
+Sarbajit Sengupta (@Sarbajit-Sengupta)
+
 Note: (@user) means a github user name.

CHANGELOG.rst

@@ -6,6 +6,9 @@ Changelog
 Unreleased
 ++++++++++
 
+- Fix f-string tokenization when a backslash precedes a replacement-field
+  brace, including raw f-strings with format specifications (#207).
+
 0.8.7 (2026-05-02)
 ++++++++++++++++++
 

parso/python/tokenize.py

@@ -114,10 +114,10 @@ def _get_token_collection(version_info):
 unicode_character_name = r'[A-Za-z0-9\-]+(?: [A-Za-z0-9\-]+)*'
 fstring_string_single_line = _compile(
     r'(?:\{\{|\}\}|\\N\{' + unicode_character_name
-    + r'\}|\\(?:\r\n?|\n)|\\[^\r\nN]|[^{}\r\n\\])+'
+    + r'\}|\\(?:\r\n?|\n)|\\[^\r\nN{}]|\\(?=[{}])|[^{}\r\n\\])+'
 )
 fstring_string_multi_line = _compile(
-    r'(?:\{\{|\}\}|\\N\{' + unicode_character_name + r'\}|\\[^N]|[^{}\\])+'
+    r'(?:\{\{|\}\}|\\N\{' + unicode_character_name + r'\}|\\[^N{}]|\\(?=[{}])|[^{}\\])+'
 )
 fstring_format_spec_single_line = _compile(r'(?:\\(?:\r\n?|\n)|[^{}\r\n])+')
 fstring_format_spec_multi_line = _compile(r'[^{}]+')

test/test_fstring_backslash_braces.py

@@ -0,0 +1,31 @@
+"""A backslash does not escape replacement-field braces in f-strings."""
+
+import ast
+
+import pytest
+
+import parso
+from parso.parser import ParserSyntaxError
+
+
+@pytest.mark.parametrize('prefix', ['rf', 'fr', 'RF', 'FR'])
+@pytest.mark.parametrize('quote', ['"', "'", '"""', "'''"])
+@pytest.mark.parametrize('slashes', [1, 2, 3])
+def test_raw_fstring_backslash_before_field(prefix, quote, slashes):
+    code = prefix + quote + '\\' * slashes + '{value:0>3o}' + quote
+    ast.parse(code)
+    grammar = parso.load_grammar(version='3.13')
+    module = grammar.parse(code, error_recovery=False)
+    assert module.get_code() == code
+    assert not list(grammar.iter_errors(module))
+    assert any(leaf.value == 'value' for leaf in module.get_used_names()['value'])
+
+
+@pytest.mark.parametrize('prefix', ['rf', 'fr'])
+@pytest.mark.parametrize('quote', ['"', '"""'])
+def test_backslash_cannot_escape_unmatched_closing_brace(prefix, quote):
+    code = prefix + quote + '\\}' + quote
+    with pytest.raises(SyntaxError):
+        ast.parse(code)
+    with pytest.raises(ParserSyntaxError):
+        parso.parse(code, version='3.13', error_recovery=False)