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Added more words about the abuse of the tp_alloc nitems argument 

perpetrated by the time and datetime classes.
This commit is contained in:
Tim Peters 2003-05-18 02:24:46 +00:00
parent 476740142d
commit 03eaf8b1ae
1 changed files with 12 additions and 1 deletions
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13
Modules/datetimemodule.c
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@ -568,7 +568,18 @@ normalize_datetime(int *year, int *month, int *day,
* setting MemoryError. All data members remain uninitialized trash.
*
* We abuse the tp_alloc "nitems" argument to communicate whether a tzinfo
* member is needed. This is ugly.
* member is needed. This is ugly, imprecise, and possibly insecure.
* tp_basicsize for the time and datetime types is set to the size of the
* struct that has room for the tzinfo member, so subclasses in Python will
* allocate enough space for a tzinfo member whether or not one is actually
* needed. That's the "ugly and imprecise" parts. The "possibly insecure"
* part is that PyType_GenericAlloc() (which subclasses in Python end up
* using) just happens today to effectively ignore the nitems argument
* when tp_itemsize is 0, which it is for these type objects. If that
* changes, perhaps the callers of tp_alloc slots in this file should
* be changed to force a 0 nitems argument unless the type being allocated
* is a base type implemented in this file (so that tp_alloc is time_alloc
* or datetime_alloc below, which know about the nitems abuse).
*/
static PyObject *