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GH-103727: Avoid advancing tokenizer too far in f-string mode #103775

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merged 1 commit into from
Apr 24, 2023
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GH-103727: Avoid advancing tokenizer too far in f-string mode #103775

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10 changes: 4 additions & 6 deletions Lib/test/test_fstring.py
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Original file line number Diff line number Diff line change
Expand Up @@ -940,15 +940,13 @@ def test_lambda(self):
"f'{lambda :x}'",
"f'{lambda *arg, :x}'",
"f'{1, lambda:x}'",
"f'{lambda x:}'",
"f'{lambda :}'",
])

# but don't emit the paren warning in general cases
self.assertAllRaise(SyntaxError,
"f-string: expecting a valid expression after '{'",
["f'{lambda x:}'",
"f'{lambda :}'",
"f'{+ lambda:None}'",
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Why are we removing the other cases?

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Just moved them up to the check for the specialized error message, since these now raise the "parenthesize your lambdas" error.

])
with self.assertRaisesRegex(SyntaxError, "f-string: expecting a valid expression after '{'"):
eval("f'{+ lambda:None}'")

def test_valid_prefixes(self):
self.assertEqual(F'{1}', "1")
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18 changes: 10 additions & 8 deletions Parser/tokenizer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2481,19 +2481,21 @@ tok_get_fstring_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct
// If we start with a bracket, we defer to the normal mode as there is nothing for us to tokenize
// before it.
int start_char = tok_nextc(tok);
int peek1 = tok_nextc(tok);
tok_backup(tok, peek1);
tok_backup(tok, start_char);

if ((start_char == '{' && peek1 != '{') || (start_char == '}' && peek1 != '}')) {
if (start_char == '{') {
if (start_char == '{') {
int peek1 = tok_nextc(tok);
tok_backup(tok, peek1);
tok_backup(tok, start_char);
if (peek1 != '{') {
current_tok->curly_bracket_expr_start_depth++;
if (current_tok->curly_bracket_expr_start_depth >= MAX_EXPR_NESTING) {
return MAKE_TOKEN(syntaxerror(tok, "f-string: expressions nested too deeply"));
}
TOK_GET_MODE(tok)->kind = TOK_REGULAR_MODE;
return tok_get_normal_mode(tok, current_tok, token);
}
TOK_GET_MODE(tok)->kind = TOK_REGULAR_MODE;
return tok_get_normal_mode(tok, current_tok, token);
}
else {
tok_backup(tok, start_char);
}

// Check if we are at the end of the string
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