## Feature There are a number of options available for formatting integers using the `format()` API. The default is `'d'`. There is a closely related alternative formatting `'n'` which works the same, but uses the locale settings to insert the correct separators. For example, `format(123456789, 'n') == '123,456,789'` (I am in the US, so my locale specifies `,` instead of `.`). The current implementation does not include the separator, and therefore `test_locale` in `test_format.py` is failing. I see two ways forward: 1. Make RustPython/Parser/format aware of `libc::locale`. This would involve adding a dependency on libc. 2. In `int.rs`, get the locale info and pass it to `rustpython_parse::FormatSpec`. This would involve adding an alternative constructor to the RustPython/Parser/format `FormatSpec` that also accepts locale info. ## Python Documentation or reference to CPython source code https://docs.python.org/3/library/string.html#formatspec, specifically the 'n' presentation type.