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bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time #20493

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May 28, 2020
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bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time #20493

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2020-05-28-17-32-29.bpo-40777.1kJU6N.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time to avoid
errors on some compilers.
13 changes: 10 additions & 3 deletions Modules/_datetimemodule.c
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Expand Up @@ -3325,7 +3325,7 @@ static PyTypeObject PyDateTime_IsoCalendarDateType = {
.tp_doc = iso_calendar_date__doc__,
.tp_methods = iso_calendar_date_methods,
.tp_getset = iso_calendar_date_getset,
.tp_base = &PyTuple_Type,
// .tp_base = &PyTuple_Type, // filled in PyInit__datetime
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The xxsubtype.c module does this weird thing with a macro called DEFERRED_ADDRESS that always returns 0:

cpython/Modules/xxsubtype.c

Line 134 in 6039851

DEFERRED_ADDRESS(&PyList_Type), /* tp_base */

Not sure exactly why it's done that way, though.

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It's just documentation:

cpython/Modules/xxsubtype.c

Lines 10 to 17 in 6039851

/* We link this module statically for convenience. If compiled as a shared
library instead, some compilers don't allow addresses of Python objects
defined in other libraries to be used in static initializers here. The
DEFERRED_ADDRESS macro is used to tag the slots where such addresses
appear; the module init function must fill in the tagged slots at runtime.
The argument is for documentation -- the macro ignores it.
*/
#define DEFERRED_ADDRESS(ADDR) 0

Would you like to use DEFERRED_ADDRESS instead?

.tp_new = iso_calendar_date_new,
};

Expand Down Expand Up @@ -4079,7 +4079,7 @@ static PyTypeObject PyDateTime_TimeZoneType = {
timezone_methods, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
&PyDateTime_TZInfoType, /* tp_base */
0, /* tp_base; filled in PyInit__datetime */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
Expand Down Expand Up @@ -6458,7 +6458,8 @@ static PyTypeObject PyDateTime_DateTimeType = {
datetime_methods, /* tp_methods */
0, /* tp_members */
datetime_getset, /* tp_getset */
&PyDateTime_DateType, /* tp_base */
0, /* tp_base; filled in
PyInit__datetime */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
Expand Down Expand Up @@ -6524,6 +6525,12 @@ PyInit__datetime(void)
if (m == NULL)
return NULL;

// `&...` is not a constant expression according to a strict reading
// of C standards. Fill tp_base at run-time rather than statically.
// See https://bugs.python.org/issue40777
PyDateTime_IsoCalendarDateType.tp_base = &PyTuple_Type;
PyDateTime_TimeZoneType.tp_base = &PyDateTime_TZInfoType;
PyDateTime_DateTimeType.tp_base = &PyDateTime_DateType;

PyTypeObject *types[] = {
&PyDateTime_DateType,
Expand Down