The PyTypeObject is the type representation of an object. We shall look at it’s structure. It is defined in the file Include/object.h.

typedef struct _typeobject {
const char *tp_name; /* For printing, in format “<module>.<name>” */
Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

/* Methods to implement standard operations */

destructor tp_dealloc;
printfunc tp_print;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
cmpfunc tp_compare;
reprfunc tp_repr;

/* Method suites for standard classes */

PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;

/* More standard operations (here for binary compatibility) */

hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;

/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;

/* Flags to define presence of optional/expanded features */
long tp_flags;

const char *tp_doc; /* Documentation string */

/* Assigned meaning in release 2.0 */
/* call function for all accessible objects */
traverseproc tp_traverse;

/* delete references to contained objects */
inquiry tp_clear;

/* Assigned meaning in release 2.1 */
/* rich comparisons */
richcmpfunc tp_richcompare;

/* weak reference enabler */
Py_ssize_t tp_weaklistoffset;

/* Added in release 2.2 */
/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;

/* Attribute descriptor and subclassing stuff */
struct PyMethodDef *tp_methods;
struct PyMemberDef *tp_members;
struct PyGetSetDef *tp_getset;
struct _typeobject *tp_base;
PyObject *tp_dict;
descrgetfunc tp_descr_get;
descrsetfunc tp_descr_set;
Py_ssize_t tp_dictoffset;
initproc tp_init;
allocfunc tp_alloc;
newfunc tp_new;
freefunc tp_free; /* Low-level free-memory routine */
inquiry tp_is_gc; /* For PyObject_IS_GC */
PyObject *tp_bases;
PyObject *tp_mro; /* method resolution order */
PyObject *tp_cache;
PyObject *tp_subclasses;
PyObject *tp_weaklist;
destructor tp_del;

/* Type attribute cache version tag. Added in version 2.6 */
unsigned int tp_version_tag;

/* these must be last and never explicitly initialized */
Py_ssize_t tp_allocs;
Py_ssize_t tp_frees;
Py_ssize_t tp_maxalloc;
struct _typeobject *tp_prev;
struct _typeobject *tp_next;

} PyTypeObject;

We shall look at the definitions of these one by one:

  1. PyObject_VAR_HEAD
    1. #define PyObject_VAR_HEAD \
      PyObject_HEAD \
      Py_ssize_t ob_size; /* Number of items in variable part */ Similar to the declaration of PyObject but contains an additional size element.
  2.  Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */ Useful for allocating memory to the object while creation.
  3. destructor tp_dealloc;
    printfunc tp_print;
    getattrfunc tp_getattr;
    setattrfunc tp_setattr;
    cmpfunc tp_compare;
    reprfunc tp_repr; // Function pointers to the appropriate operations which is fairly straight forward to understand.
  4. PyNumberMethods *tp_as_number;
    PySequenceMethods *tp_as_sequence;
    PyMappingMethods *tp_as_mapping; // Methods for performing numerical, sequence and mapping methods. The definitions for these objects is found in object.h line number 219, 275 and 289 respectively.
  5. hashfunc tp_hash; // The hash function.
  6. getiterfunc tp_iter;
    iternextfunc tp_iternext; // For managing the object as an iterator.
  7. struct PyMethodDef *tp_methods;
    struct PyMemberDef *tp_members; // For user defined functions and members.

I shall leave the rest as self study as they are quite straight forward from their names.


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