What does ob_size reprensents in the structure of long integer?

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The integer (long) type definition effectively looks like this (once the C macros are expanded):

struct _longobject {
  long ob_refcnt;
  PyTypeObject *ob_type;
  size_t ob_size;
  uint32_t ob_digit[1];
  };

Here, what does ob_size mean and what its value represents?

cpython python
1 Answers

Python _longobject (A.K.A. int) is variable size and that is the standard python header for variable objects. From object.h:

/* PyObject_VAR_HEAD defines the initial segment of all variable-size
 * container objects.  These end with a declaration of an array with 1
 * element, but enough space is malloc'ed so that the array actually
 * has room for ob_size elements.  Note that ob_size is an element count,
 * not necessarily a byte count.
 */

_longobject is allocated on the heap in a memory block large enough to hold long ob_digit[ob_size] long integers.

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