Python f-strings: highlight expressions in curly braces

Fixes #1228

2 files changed, 788 insertions, 15 deletions

diff --git a/pygments/lexers/python.py b/pygments/lexers/python.py
index 8e1debac..24067d59 100644
--- a/pygments/lexers/python.py
+++ b/pygments/lexers/python.py
@@ -85,6 +85,20 @@ class PythonLexer(RegexLexer):
             # newlines are an error (use "nl" state)
         ]
 
+    def fstring_rules(ttype):
+        return [
+            # Assuming that a '}' is the closing brace after format specifier.
+            # Sadly, this means that we won't detect syntax error. But it's
+            # more important to parse correct syntax correctly, than to
+            # highlight invalid syntax.
+            (r'\}', String.Interpol),
+            (r'\{', String.Interpol, 'expr-inside-fstring'),
+            # backslashes, quotes and formatting signs must be parsed one at a time
+            (r'[^\\\'"{}\n]+', ttype),
+            (r'[\'"\\]', ttype),
+            # newlines are an error (use "nl" state)
+        ]
+
     tokens = {
         'root': [
             (r'\n', Text),
@@ -92,14 +106,10 @@ class PythonLexer(RegexLexer):
              bygroups(Text, String.Affix, String.Doc)),
             (r"^(\s*)([rRuUbB]{,2})('''(?:.|\n)*?''')",
              bygroups(Text, String.Affix, String.Doc)),
-            (r'[^\S\n]+', Text),
             (r'\A#!.+$', Comment.Hashbang),
             (r'#.*$', Comment.Single),
-            (r'!=|==|<<|>>|:=|[-~+/*%=<>&^|.]', Operator),
-            (r'[]{}:(),;[]', Punctuation),
             (r'\\\n', Text),
             (r'\\', Text),
-            (r'(in|is|and|or|not)\b', Operator.Word),
             include('keywords'),
             (r'(def)((?:\s|\\\s)+)', bygroups(Keyword, Text), 'funcname'),
             (r'(class)((?:\s|\\\s)+)', bygroups(Keyword, Text), 'classname'),
@@ -107,30 +117,84 @@ class PythonLexer(RegexLexer):
              'fromimport'),
             (r'(import)((?:\s|\\\s)+)', bygroups(Keyword.Namespace, Text),
              'import'),
-            include('builtins'),
-            include('magicfuncs'),
-            include('magicvars'),
+            include('expr'),
+        ],
+        'expr': [
+            # raw f-strings
+            ('(?i)(rf|fr)(""")',
+             bygroups(String.Affix, String.Double), 'tdqf'),
+            ("(?i)(rf|fr)(''')",
+             bygroups(String.Affix, String.Single), 'tsqf'),
+            ('(?i)(rf|fr)(")',
+             bygroups(String.Affix, String.Double), 'dqf'),
+            ("(?i)(rf|fr)(')",
+             bygroups(String.Affix, String.Single), 'sqf'),
+            # non-raw f-strings
+            ('([fF])(""")', bygroups(String.Affix, String.Double),
+             combined('fstringescape', 'tdqf')),
+            ("([fF])(''')", bygroups(String.Affix, String.Single),
+             combined('fstringescape', 'tsqf')),
+            ('([fF])(")', bygroups(String.Affix, String.Double),
+             combined('fstringescape', 'dqf')),
+            ("([fF])(')", bygroups(String.Affix, String.Single),
+             combined('fstringescape', 'sqf')),
             # raw strings
-            ('(?i)(rb|br|fr|rf|r)(""")',
+            ('(?i)(rb|br|r)(""")',
              bygroups(String.Affix, String.Double), 'tdqs'),
-            ("(?i)(rb|br|fr|rf|r)(''')",
+            ("(?i)(rb|br|r)(''')",
              bygroups(String.Affix, String.Single), 'tsqs'),
-            ('(?i)(rb|br|fr|rf|r)(")',
+            ('(?i)(rb|br|r)(")',
              bygroups(String.Affix, String.Double), 'dqs'),
-            ("(?i)(rb|br|fr|rf|r)(')",
+            ("(?i)(rb|br|r)(')",
              bygroups(String.Affix, String.Single), 'sqs'),
             # non-raw strings
-            ('([uUbBfF]?)(""")', bygroups(String.Affix, String.Double),
+            ('([uUbB]?)(""")', bygroups(String.Affix, String.Double),
              combined('stringescape', 'tdqs')),
-            ("([uUbBfF]?)(''')", bygroups(String.Affix, String.Single),
+            ("([uUbB]?)(''')", bygroups(String.Affix, String.Single),
              combined('stringescape', 'tsqs')),
-            ('([uUbBfF]?)(")', bygroups(String.Affix, String.Double),
+            ('([uUbB]?)(")', bygroups(String.Affix, String.Double),
              combined('stringescape', 'dqs')),
-            ("([uUbBfF]?)(')", bygroups(String.Affix, String.Single),
+            ("([uUbB]?)(')", bygroups(String.Affix, String.Single),
              combined('stringescape', 'sqs')),
+            (r'[^\S\n]+', Text),
+            (r'!=|==|<<|>>|:=|[-~+/*%=<>&^|.]', Operator),
+            (r'[]{}:(),;[]', Punctuation),
+            (r'(in|is|and|or|not)\b', Operator.Word),
+            include('expr-keywords'),
+            include('builtins'),
+            include('magicfuncs'),
+            include('magicvars'),
             include('name'),
             include('numbers'),
         ],
+        'expr-inside-fstring': [
+            (r'[{([]', Punctuation, 'expr-inside-fstring-inner'),
+            # without format specifier
+            (r'(=\s*)?'         # debug (https://bugs.python.org/issue36817)
+             r'(\![sraf])?'     # conversion
+             r'}', String.Interpol, '#pop'),
+            # with format specifier
+            # we'll catch the remaining '}' in the outer scope
+            (r'(=\s*)?'         # debug (https://bugs.python.org/issue36817)
+             r'(\![sraf])?'     # conversion
+             r':', String.Interpol, '#pop'),
+            (r'[^\S]+', Text),  # allow new lines
+            include('expr'),
+        ],
+        'expr-inside-fstring-inner': [
+            (r'[{([]', Punctuation, 'expr-inside-fstring-inner'),
+            (r'[])}]', Punctuation, '#pop'),
+            (r'[^\S]+', Text),  # allow new lines
+            include('expr'),
+        ],
+        'expr-keywords': [
+            # Based on https://docs.python.org/3/reference/expressions.html
+            (words((
+                'async for', 'await', 'else', 'for', 'if', 'lambda',
+                'yield', 'yield from'), suffix=r'\b'),
+             Keyword),
+            (words(('True', 'False', 'None'), suffix=r'\b'), Keyword.Constant),
+        ],
         'keywords': [
             (words((
                 'assert', 'async', 'await', 'break', 'continue', 'del', 'elif',
@@ -252,12 +316,29 @@ class PythonLexer(RegexLexer):
             (uni_name, Name.Namespace),
             default('#pop'),
         ],
+        'fstringescape': [
+            ('{{', String.Escape),
+            ('}}', String.Escape),
+            include('stringescape'),
+        ],
         'stringescape': [
             (r'\\([\\abfnrtv"\']|\n|N\{.*?\}|u[a-fA-F0-9]{4}|'
              r'U[a-fA-F0-9]{8}|x[a-fA-F0-9]{2}|[0-7]{1,3})', String.Escape)
         ],
+        'fstrings-single': fstring_rules(String.Single),
+        'fstrings-double': fstring_rules(String.Double),
         'strings-single': innerstring_rules(String.Single),
         'strings-double': innerstring_rules(String.Double),
+        'dqf': [
+            (r'"', String.Double, '#pop'),
+            (r'\\\\|\\"|\\\n', String.Escape),  # included here for raw strings
+            include('fstrings-double')
+        ],
+        'sqf': [
+            (r"'", String.Single, '#pop'),
+            (r"\\\\|\\'|\\\n", String.Escape),  # included here for raw strings
+            include('fstrings-single')
+        ],
         'dqs': [
             (r'"', String.Double, '#pop'),
             (r'\\\\|\\"|\\\n', String.Escape),  # included here for raw strings
@@ -268,6 +349,16 @@ class PythonLexer(RegexLexer):
             (r"\\\\|\\'|\\\n", String.Escape),  # included here for raw strings
             include('strings-single')
         ],
+        'tdqf': [
+            (r'"""', String.Double, '#pop'),
+            include('fstrings-double'),
+            (r'\n', String.Double)
+        ],
+        'tsqf': [
+            (r"'''", String.Single, '#pop'),
+            include('fstrings-single'),
+            (r'\n', String.Single)
+        ],
         'tdqs': [
             (r'"""', String.Double, '#pop'),
             include('strings-double'),
diff --git a/tests/test_python.py b/tests/test_python.py
index b0922adf..23bb6ed1 100644
--- a/tests/test_python.py
+++ b/tests/test_python.py
@@ -12,6 +12,8 @@ import pytest
 from pygments.lexers import PythonLexer, Python3Lexer
 from pygments.token import Token
 
+import re
+
 
 @pytest.fixture(scope='module')
 def lexer2():
@@ -158,3 +160,683 @@ def test_walrus_operator(lexer3):
         (Token.Text, '\n'),
     ]
     assert list(lexer3.get_tokens(fragment)) == tokens
+
+
+def test_fstring(lexer3):
+    """
+    Tests that the lexer can parse f-strings
+    """
+    fragments_and_tokens = (
+        # examples from PEP-0498
+        (
+            "f'My name is {name}, my age next year is {age+1}, my anniversary is {anniversary:%A, %B %d, %Y}.'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'My name is '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'name'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ', my age next year is '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'age'),
+                (Token.Operator, '+'),
+                (Token.Literal.Number.Integer, '1'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ', my anniversary is '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'anniversary'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Single, '%A, %B %d, %Y'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '.'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, u'\n')
+            ]
+        ), (
+            "f'He said his name is {name!r}.'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'He said his name is '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'name'),
+                (Token.Literal.String.Interpol, '!r}'),
+                (Token.Literal.String.Single, '.'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+
+        ), (
+            "f'input={value:#06x}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'input='),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'value'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Single, '#06x'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'{"quoted string"}'\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Double, 'quoted string'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'{f"{inner}"}'\n""",  # not in the PEP
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'inner'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            # SyntaxError: f-string expression part cannot include a backslash
+            "f'{\\'quoted string\\'}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Error, '\\'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'quoted string'),
+                (Token.Literal.String.Escape, "\\'"),
+                (Token.Literal.String.Single, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{{ {4*10} }}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Escape, '{{'),
+                (Token.Literal.String.Single, ' '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.Number.Integer, '4'),
+                (Token.Operator, '*'),
+                (Token.Literal.Number.Integer, '10'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ' '),
+                (Token.Literal.String.Escape, '}}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{{{4*10}}}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Escape, '{{'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.Number.Integer, '4'),
+                (Token.Operator, '*'),
+                (Token.Literal.Number.Integer, '10'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Escape, '}}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "fr'x={4*10}'\n",
+            [
+                (Token.Literal.String.Affix, 'fr'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, "x="),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.Number.Integer, '4'),
+                (Token.Operator, '*'),
+                (Token.Literal.Number.Integer, '10'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'abc {a["x"]} def'\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'abc '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'a'),
+                (Token.Punctuation, '['),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Double, 'x'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ' def'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'''abc {a['x']} def'''\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Literal.String.Single, 'abc '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'a'),
+                (Token.Punctuation, '['),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'x'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ' def'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'''{x
++1}'''\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'x'),
+                (Token.Text, '\n'),
+                (Token.Operator, '+'),
+                (Token.Literal.Number.Integer, '1'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'''{d[0
+]}'''\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'd'),
+                (Token.Punctuation, '['),
+                (Token.Literal.Number.Integer, '0'),
+                (Token.Text, '\n'),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'result: {value:{width}.{precision}}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'result: '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'value'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'width'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '.'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'precision'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "'a' 'b' f'{x}' '{c}' f'str<{y:^4}>' 'd' 'e'\n",
+            [
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'a'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'b'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'x'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{c}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'str<'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'y'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Single, '^4'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '>'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'd'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, ' '),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'e'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{i}:{d[i]}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'i'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ':'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'd'),
+                (Token.Punctuation, '['),
+                (Token.Name, 'i'),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'x = {x:+3}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, "x = "),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'x'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Single, '+3'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{fn(lst,2)} {fn(lst,3)}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'fn'),
+                (Token.Punctuation, '('),
+                (Token.Name, 'lst'),
+                (Token.Punctuation, ','),
+                (Token.Literal.Number.Integer, '2'),
+                (Token.Punctuation, ')'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ' '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'fn'),
+                (Token.Punctuation, '('),
+                (Token.Name, 'lst'),
+                (Token.Punctuation, ','),
+                (Token.Literal.Number.Integer, '3'),
+                (Token.Punctuation, ')'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'mapping is { {a:b for (a, b) in ((1, 2), (3, 4))} }'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'mapping is '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Text, ' '),
+                (Token.Punctuation, '{'),
+                (Token.Name, 'a'),
+                (Token.Punctuation, ':'),
+                (Token.Name, 'b'),
+                (Token.Text, ' '),
+                (Token.Keyword, 'for'),
+                (Token.Text, ' '),
+                (Token.Punctuation, '('),
+                (Token.Name, 'a'),
+                (Token.Punctuation, ','),
+                (Token.Text, ' '),
+                (Token.Name, 'b'),
+                (Token.Punctuation, ')'),
+                (Token.Text, ' '),
+                (Token.Operator.Word, 'in'),
+                (Token.Text, ' '),
+                (Token.Punctuation, '('),
+                (Token.Punctuation, '('),
+                (Token.Literal.Number.Integer, '1'),
+                (Token.Punctuation, ','),
+                (Token.Text, ' '),
+                (Token.Literal.Number.Integer, '2'),
+                (Token.Punctuation, ')'),
+                (Token.Punctuation, ','),
+                (Token.Text, ' '),
+                (Token.Punctuation, '('),
+                (Token.Literal.Number.Integer, '3'),
+                (Token.Punctuation, ','),
+                (Token.Text, ' '),
+                (Token.Literal.Number.Integer, '4'),
+                (Token.Punctuation, ')'),
+                (Token.Punctuation, ')'),
+                (Token.Punctuation, '}'),
+                (Token.Text, ' '),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f'a={d["a"]}'\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'a='),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'd'),
+                (Token.Punctuation, '['),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Double, 'a'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'a={d[a]}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, 'a='),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'd'),
+                (Token.Punctuation, '['),
+                (Token.Name, 'a'),
+                (Token.Punctuation, ']'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "fr'{header}:\\s+'\n",
+            [
+                (Token.Literal.String.Affix, 'fr'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'header'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ':'),
+                (Token.Literal.String.Single, '\\'),
+                (Token.Literal.String.Single, 's+'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{a!r}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'a'),
+                (Token.Literal.String.Interpol, '!r}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{(lambda x: x*2)(3)}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Punctuation, '('),
+                (Token.Keyword, 'lambda'),
+                (Token.Text, ' '),
+                (Token.Name, 'x'),
+                (Token.Punctuation, ':'),
+                (Token.Text, ' '),
+                (Token.Name, 'x'),
+                (Token.Operator, '*'),
+                (Token.Literal.Number.Integer, '2'),
+                (Token.Punctuation, ')'),
+                (Token.Punctuation, '('),
+                (Token.Literal.Number.Integer, '3'),
+                (Token.Punctuation, ')'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "extra = f'{extra},waiters:{len(self._waiters)}'\n",
+            [
+                (Token.Name, 'extra'),
+                (Token.Text, ' '),
+                (Token.Operator, '='),
+                (Token.Text, ' '),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'extra'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, ',waiters:'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name.Builtin, 'len'),
+                (Token.Punctuation, '('),
+                (Token.Name.Builtin.Pseudo, 'self'),
+                (Token.Operator, '.'),
+                (Token.Name, '_waiters'),
+                (Token.Punctuation, ')'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            'message.append(f" [line {lineno:2d}]")\n',
+            [
+                (Token.Name, 'message'),
+                (Token.Operator, '.'),
+                (Token.Name, 'append'),
+                (Token.Punctuation, '('),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Double, ' [line '),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'lineno'),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Double, '2d'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Double, ']'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Punctuation, ')'),
+                (Token.Text, '\n')
+            ]
+        ),
+        # Examples from https://bugs.python.org/issue36817
+        (
+            'f"{foo=}"\n',
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'foo'),
+                (Token.Literal.String.Interpol, '=}'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'{foo=!s}'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'foo'),
+                (Token.Literal.String.Interpol, '=!s}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            'f"{math.pi=!f:.2f}"\n',
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'math'),
+                (Token.Operator, '.'),
+                (Token.Name, 'pi'),
+                (Token.Literal.String.Interpol, '=!f:'),
+                (Token.Literal.String.Double, '.2f'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Text, '\n')
+            ]
+        ), (
+            'f"{ chr(65) =}"\n',
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Text, ' '),
+                (Token.Name.Builtin, 'chr'),
+                (Token.Punctuation, '('),
+                (Token.Literal.Number.Integer, '65'),
+                (Token.Punctuation, ')'),
+                (Token.Text, ' '),
+                (Token.Literal.String.Interpol, '=}'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Text, '\n')
+            ]
+        ), (
+            'f"{chr(65) = }"\n',
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name.Builtin, 'chr'),
+                (Token.Punctuation, '('),
+                (Token.Literal.Number.Integer, '65'),
+                (Token.Punctuation, ')'),
+                (Token.Text, ' '),
+                (Token.Literal.String.Interpol, '= }'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'*{n=:30}*'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'n'),
+                (Token.Literal.String.Interpol, '=:'),
+                (Token.Literal.String.Single, '30'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'*{n=!r:30}*'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'n'),
+                (Token.Literal.String.Interpol, '=!r:'),
+                (Token.Literal.String.Single, '30'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """f"*{f'{n=}':30}*"\n""",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Literal.String.Double, '*'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'n'),
+                (Token.Literal.String.Interpol, '=}'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Interpol, ':'),
+                (Token.Literal.String.Double, '30'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Double, '*'),
+                (Token.Literal.String.Double, '"'),
+                (Token.Text, '\n')
+            ]
+        ), (
+            "f'*{n=:+<30}*'\n",
+            [
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'n'),
+                (Token.Literal.String.Interpol, '=:'),
+                (Token.Literal.String.Single, '+<30'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, '*'),
+                (Token.Literal.String.Single, "'"),
+                (Token.Text, '\n')
+            ]
+        ), (
+            """
+   f'''{foo
+         = !s:20}'''\n""",
+            [
+                (Token.Text, '   '),
+                (Token.Literal.String.Affix, 'f'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Literal.String.Interpol, '{'),
+                (Token.Name, 'foo'),
+                (Token.Text, '\n         '),
+                (Token.Literal.String.Interpol, '= !s:'),
+                (Token.Literal.String.Single, '20'),
+                (Token.Literal.String.Interpol, '}'),
+                (Token.Literal.String.Single, "'''"),
+                (Token.Text, '\n')
+            ]
+        )
+
+    )
+
+    for fragment,tokens in fragments_and_tokens:
+        assert list(lexer3.get_tokens(fragment)) == tokens
+
+    # Now switch between single and double quotes, to cover both cases equally
+    rep = {"'":'"', '"':"'"}
+    pattern = re.compile("|".join(rep.keys()))
+    for fragment,tokens in fragments_and_tokens:
+        fragment = pattern.sub(lambda m: rep[m.group(0)], fragment)
+        tokens = list(tokens)
+        for i,(token,match) in enumerate(tokens):
+            if token == Token.Literal.String.Single:
+                token = Token.Literal.String.Double
+            elif token == Token.Literal.String.Double:
+                token = Token.Literal.String.Single
+            match = pattern.sub(lambda m: rep[m.group(0)], match)
+            tokens[i] = (token, match)
+        assert list(lexer3.get_tokens(fragment)) == tokens