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support None for const char* arg, with minimal overhead #683

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@wojdyr wojdyr commented Aug 13, 2024

Since pybind11 also accepts None for const char* as an exception among built-in types, remove a paragraph about differences in porting.rst.

The overhead is minimal. Checking the size of test_functions_ext.cpython-311-x86_64-linux-gnu.so built with -O3, it increased only by 32 bytes.

I'm aware that it's possible to use std::optional<const char*>, but to me it looks more awkward than std::optional<int>, perhaps because const char*, unlike std::string, looks already optional.


There is a third place in docs where None arg is covered:

nanobind/docs/functions.rst

Lines 178 to 181 in 8e5fd14

Note that passing values *by pointer* (including null pointers) is only
supported for :ref:`bound <bindings>` types. :ref:`Type casters <type_casters>`
and :ref:`wrappers <wrappers>` cannot be used in such cases and will produce
compile-time errors.

Perhaps it's outdated, because having argument such as int* works fine, just doesn't accept None. Or I misunderstand it. Anyway, I didn't try to edit it.

Since pybind11 also accepts None for const char* as an exception among
built-in types, remove a paragraph about differences in porting.rst.
@wjakob wjakob force-pushed the master branch 2 times, most recently from f9e5e0b to 30e96b7 Compare September 9, 2024 14:54
wojdyr added a commit to project-gemmi/gemmi that referenced this pull request Sep 13, 2024
Please report problems when you find them.

notes and changes
-----------------

Protocol Buffer is currently not supported by nanobind.
Adding GridBase.__array__() for NumPy interoperability
in many cases works as seemless replacement of the Protocol Buffer.

Implicit list->ndarray conversion is also not supported, but is welcomed:
wjakob/nanobind#327

None is not accepted by default, an annotation must be added.
I may have missed it in some functions - let me know.
In case of const char* arg, None is not supported at all; I proposed it
upstream: wjakob/nanobind#683

For default nullptr, using nb::arg()=nb::none() instead of =nullptr.
Both work, but the latter seems to be more canonical in nanobind.

In nanobind 2.x using make_iterator and bind_vector+__getitem__ returns
copies, not references, by default. We usually prefer to avoid copying.
Added a helper function usual_iterator() that uses old rv_policy.

gemmi.ValueSigmaAsuData.value_array: previously had so-called
structured data type, now it has shape (N,2) with dtype=float32.

Added pickling support for Structure, Model, Chain, Residue, Atom, UnitCell.

Notes about pickling of SpaceGroup:
wjakob/nanobind#670
In a follow up, picking of SpaceGroup was optimized, replacing xhm()
with an index. The gain was modest (pickling and unpickling a list of all
SpaceGroups from the built-in table was reduced from ~1ms, to ~0.5ms).
It might not be safe - multiple copies of the table may exist.

Notes about constructors for PdbWriteOptions and MmcifOutputGroups:
see wjakob/nanobind#664

doctests: many changes, mostly because __repr__ of enums
and of bind_vector-ed classes in nanobind is different than in pybind11

added alignas(8) to HklValue: in nanobind array bindings,
stride is given as a number of elements, not bytes.
This was a problem for ComplexAsuData.value_array:
sizeof(HklValue) was 20 (3*4+2*4) which is not a multiple of 8.

Functions IT92Coef.calculate_sf() and IT92Coef.calculate_density_iso()
used to be vectorized (could take numpy array as arg), now they aren't,
let me know if you need a vectorized version.

Not yet done: *.pyi files with type annotations

Planned: unified logging of warnings/errors from various gemmi functions
@wjakob wjakob force-pushed the master branch 2 times, most recently from f3e2796 to bff96e2 Compare October 4, 2024 03:20
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