Deprecated since 3.14, removed in 3.19. For historical reasons, if _pack_ is non-zero, the MSVC-compatible layout will be used by default. On non-Windows platforms, this default is deprecated and is slated to become an error in Python 3.19. If it is intended, set _layout_ to 'ms' explicitly.
An optional small integer that allows overriding the alignment of structure fields in the instance.