Bug report

Bug description:

>>>value=123>>>f"{value:.{'2'}f}"# '123.00'>>>f"{value:.{'2f'}}"# '123.00'# but, shouldn't this one below also be valid?>>>f"{value:.... {'2'}f}"# invalid>>>f"{value:... {'.2f'}}"# '123.00'

I am checking the code of CPython's lexer and am confused why the lexer resets to normal mode when it encounters line break in format spec

Go back to the original PR:#110271
Seems this case is not covered by the test cases

The case above could be recognized by tokenizer, so maybe pegen should be modified.
However, since it goes back to normal mode, some corner cases cannot be handled by tokenizer:

>>>value=123>>>f"{value:#{'x'}}"# '0x7b'>>>f"{value:... #{'x'}}"# breaks the tokenizer

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Linked PRs

• gh-129958: Properly disallow newlines in format specs in single-quoted f-strings #130063
• [3.13] gh-129958: Properly disallow newlines in format specs in single-quoted f-strings (GH-130063) #132692
• gh-129958: New syntax error in format spec applies to both f-strings and t-strings #135570
• [3.14] gh-129958: New syntax error in format spec applies to both f-strings and t-strings (GH-135570) #135982