`ctypes.util.struct` example does not run and `layout` looks required

[fedonman]

Documentation

The second @struct example in Doc/library/ctypes.rst cannot be run: it uses Annotated, CFieldInfo, c_ssize_t and c_void_p, and the page imports none of them. Carrying over the imports from the first example directly above it is not enough either.

$ ./python -c '
from ctypes.util import struct
from ctypes import c_int

@struct
class PyObject:
   ob_refcnt: c_ssize_t
   ob_type: c_void_p
'
Traceback (most recent call last):
  ...
  File "<string>", line 7, in __annotate__
    ob_refcnt: c_ssize_t
               ^^^^^^^^^
NameError: name 'c_ssize_t' is not defined

The same entry's signature line is struct(*, align=None, layout, endian='native', pack=None), which renders layout as a required parameter. ctypes.util.struct gives it a default:

$ ./python -c "import inspect, ctypes.util; print(inspect.signature(ctypes.util.struct))"
(class_or_none=None, /, *, align=None, layout=None, endian='native', pack=None)

Expected: the example runs as written, and layout is documented as layout=None.

Linked PRs

• gh-157208: Fix the ctypes.util.struct documentation #157209