# Support hexadecimal floating-point literals

**URL:** <https://discuss.python.org/t/support-hexadecimal-floating-point-literals/41848>\
**Category:** Ideas\
**Created:** [December 25, 2023, 3:10am UTC](https://discuss.python.org/t/support-hexadecimal-floating-point-literals/41848 "2023-12-25T03:10:43Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![mdickinson](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/mdickinson/32/976_2.png) [@mdickinson](https://discuss.python.org/u/mdickinson)\
**Post date:** [January 1, 2024, 11:29am UTC](https://discuss.python.org/t/support-hexadecimal-floating-point-literals/41848/4 "2024-01-01T11:29:40Z")

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> [@skirpichev](#):
>
> Let me know if it worth a pr. And, if so, does this require a PEP?

For the language syntax change, I think we should have a PEP. There needs to be a case made that the benefits are big enough to warrant syntax changes, and there are some choices to make that it would be good to discuss and record. It’s worth noting that something like `0x1.bp-4` is _already_ valid at the syntax level (even though it’s not particularly useful, since there’s no `bp` attribute on integers).

```python
>>> print(ast.dump(ast.parse("0x1.bp-4", mode="eval"), indent=4))
Expression(
    body=BinOp(
        left=Attribute(
            value=Constant(value=1),
            attr='bp',
            ctx=Load()),
        op=Sub(),
        right=Constant(value=4)))

```

If we start allowing `.` in `0x` literals, then there’s also the question of whether something like `0x1.bit_length` should remain legal syntax, or whether it should become illegal in the same way that `1.bit_length` currently is. If it stays legal, what are the exact rules for determining when something like `0x1.abc` is interpreted as a hex floating-point literal and when it’s interpreted as an attribute access on an integer?

For the formatting addition, I think a careful and complete description of the proposed new functionality in a GitHub issue would be enough, though again there are many details to be determined. BTW, why not presentation type `x`, with semantics similar to those of `x` for `int`? So the `0x` prefix would be omitted unless using `#x`.

E.g., we already have:

```python
>>> format(123, 'x')
'7b'
>>> format(123, '#x')
'0x7b'

```

and I’d propose something along the lines of

```python
>>> format(123.4, 'x')
'1.ed9999999999ap+6'
>>> format(123.4, '#x')
'0x1.ed9999999999ap+6'

```

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