typedef struct {
 PyObject_VAR_HEAD
 /* Vector of pointers to list elements. list[0] is ob_item[0], etc. */
 PyObject **ob_item;
 
 /* ob_item contains space for 'allocated' elements. The number
 * currently in use is ob_size.
 * Invariants:
 * 0 <= ob_size <= allocated
 * len(list) == ob_size
 * ob_item == NULL implies ob_size == allocated == 0
 * list.sort() temporarily sets allocated to -1 to detect mutations.
 *
 * Items must normally not be NULL, except during construction when
 * the list is not yet visible outside the function that builds it.
 */
 Py_ssize_t allocated;
} PyListObject;

/* PyDict_MINSIZE is the minimum size of a dictionary. This many slots are
 * allocated directly in the dict object (in the ma_smalltable member).
 * It must be a power of 2, and at least 4. 8 allows dicts with no more
 * than 5 active entries to live in ma_smalltable (and so avoid an
 * additional malloc); instrumentation suggested this suffices for the
 * majority of dicts (consisting mostly of usually-small instance dicts and
 * usually-small dicts created to pass keyword arguments).
 */
#define PyDict_MINSIZE 8
 
typedef struct {
 /* Cached hash code of me_key. Note that hash codes are C longs.
 * We have to use Py_ssize_t instead because dict_popitem() abuses
 * me_hash to hold a search finger.
 */
 Py_ssize_t me_hash;
 PyObject *me_key;
 PyObject *me_value;
} PyDictEntry;
 
/*
To ensure the lookup algorithm terminates, there must be at least one Unused
slot (NULL key) in the table.
The value ma_fill is the number of non-NULL keys (sum of Active and Dummy);
ma_used is the number of non-NULL, non-dummy keys (== the number of non-NULL
values == the number of Active items).
To avoid slowing down lookups on a near-full table, we resize the table when
it's two-thirds full.
*/
typedef struct _dictobject PyDictObject;
struct _dictobject {
 PyObject_HEAD
 Py_ssize_t ma_fill; /* # Active + # Dummy */
 Py_ssize_t ma_used; /* # Active */
 
 /* The table contains ma_mask + 1 slots, and that's a power of 2.
 * We store the mask instead of the size because the mask is more
 * frequently needed.
 */
 Py_ssize_t ma_mask;
 
 /* ma_table points to ma_smalltable for small tables, else to
 * additional malloc'ed memory. ma_table is never NULL! This rule
 * saves repeated runtime null-tests in the workhorse getitem and
 * setitem calls.
 */
 PyDictEntry *ma_table;
 PyDictEntry *(*ma_lookup)(PyDictObject *mp, PyObject *key, long hash);
 PyDictEntry ma_smalltable[PyDict_MINSIZE];
};

#ifdef Py_TRACE_REFS
/* Define pointers to support a doubly-linked list of all live heap objects. */
#define _PyObject_HEAD_EXTRA   struct _object *_ob_next;   struct _object *_ob_prev;
 
#define _PyObject_EXTRA_INIT 0, 0,
 
#else
#define _PyObject_HEAD_EXTRA
#define _PyObject_EXTRA_INIT
#endif
 
/* PyObject_HEAD defines the initial segment of every PyObject. */
#define PyObject_HEAD    _PyObject_HEAD_EXTRA   Py_ssize_t ob_refcnt;   struct _typeobject *ob_type;

/* 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.
 */
#define PyObject_VAR_HEAD   PyObject_HEAD    Py_ssize_t ob_size; /* Number of items in variable part */

#!/usr/bin/env python

class Foobar(object):
 def __init__(self, x):
 self.x = x

@profile
def main():
 f = [Foobar(42) for i in range(1000000)]

if __name__ == "__main__":
 main()

#!/usr/bin/env python

class Foobar(object):
 __slots__ = 'x'
 def __init__(self, x):
 self.x = x
@profile
def main():
 f = [Foobar(42) for i in range(1000000)]

if __name__ == "__main__":
 main()