Dictionary Objects
******************

type PyDictObject

   This subtype of "PyObject" represents a Python dictionary object.

PyTypeObject PyDict_Type
    * Part of the Stable ABI.*

   This instance of "PyTypeObject" represents the Python dictionary
   type.  This is the same object as "dict" in the Python layer.

int PyDict_Check(PyObject *p)

   Return true if *p* is a dict object or an instance of a subtype of
   the dict type.  This function always succeeds.

int PyDict_CheckExact(PyObject *p)

   Return true if *p* is a dict object, but not an instance of a
   subtype of the dict type.  This function always succeeds.

PyObject *PyDict_New()
    *Return value: New reference.** Part of the Stable ABI.*

   Return a new empty dictionary, or "NULL" on failure.

PyObject *PyDictProxy_New(PyObject *mapping)
    *Return value: New reference.** Part of the Stable ABI.*

   Return a "types.MappingProxyType" object for a mapping which
   enforces read-only behavior.  This is normally used to create a
   view to prevent modification of the dictionary for non-dynamic
   class types.

void PyDict_Clear(PyObject *p)
    * Part of the Stable ABI.*

   Empty an existing dictionary of all key-value pairs.

int PyDict_Contains(PyObject *p, PyObject *key)
    * Part of the Stable ABI.*

   Determine if dictionary *p* contains *key*.  If an item in *p* is
   matches *key*, return "1", otherwise return "0".  On error, return
   "-1". This is equivalent to the Python expression "key in p".

PyObject *PyDict_Copy(PyObject *p)
    *Return value: New reference.** Part of the Stable ABI.*

   Return a new dictionary that contains the same key-value pairs as
   *p*.

int PyDict_SetItem(PyObject *p, PyObject *key, PyObject *val)
    * Part of the Stable ABI.*

   Insert *val* into the dictionary *p* with a key of *key*.  *key*
   must be *hashable*; if it isn’t, "TypeError" will be raised. Return
   "0" on success or "-1" on failure.  This function *does not* steal
   a reference to *val*.

int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)
    * Part of the Stable ABI.*

   This is the same as "PyDict_SetItem()", but *key* is specified as a
   const char* UTF-8 encoded bytes string, rather than a PyObject*.

int PyDict_DelItem(PyObject *p, PyObject *key)
    * Part of the Stable ABI.*

   Remove the entry in dictionary *p* with key *key*. *key* must be
   *hashable*; if it isn’t, "TypeError" is raised. If *key* is not in
   the dictionary, "KeyError" is raised. Return "0" on success or "-1"
   on failure.

int PyDict_DelItemString(PyObject *p, const char *key)
    * Part of the Stable ABI.*

   This is the same as "PyDict_DelItem()", but *key* is specified as a
   const char* UTF-8 encoded bytes string, rather than a PyObject*.

PyObject *PyDict_GetItem(PyObject *p, PyObject *key)
    *Return value: Borrowed reference.** Part of the Stable ABI.*

   Return the object from dictionary *p* which has a key *key*.
   Return "NULL" if the key *key* is not present, but *without*
   setting an exception.

   Note:

     Exceptions that occur while this calls "__hash__()" and
     "__eq__()" methods are silently ignored. Prefer the
     "PyDict_GetItemWithError()" function instead.

   Changed in version 3.10: Calling this API without *GIL* held had
   been allowed for historical reason. It is no longer allowed.

PyObject *PyDict_GetItemWithError(PyObject *p, PyObject *key)
    *Return value: Borrowed reference.** Part of the Stable ABI.*

   Variant of "PyDict_GetItem()" that does not suppress exceptions.
   Return "NULL" **with** an exception set if an exception occurred.
   Return "NULL" **without** an exception set if the key wasn’t
   present.

PyObject *PyDict_GetItemString(PyObject *p, const char *key)
    *Return value: Borrowed reference.** Part of the Stable ABI.*

   This is the same as "PyDict_GetItem()", but *key* is specified as a
   const char* UTF-8 encoded bytes string, rather than a PyObject*.

   Note:

     Exceptions that occur while this calls "__hash__()" and
     "__eq__()" methods or while creating the temporary "str" object
     are silently ignored. Prefer using the
     "PyDict_GetItemWithError()" function with your own
     "PyUnicode_FromString()" *key* instead.

PyObject *PyDict_SetDefault(PyObject *p, PyObject *key, PyObject *defaultobj)
    *Return value: Borrowed reference.*

   This is the same as the Python-level "dict.setdefault()".  If
   present, it returns the value corresponding to *key* from the
   dictionary *p*.  If the key is not in the dict, it is inserted with
   value *defaultobj* and *defaultobj* is returned.  This function
   evaluates the hash function of *key* only once, instead of
   evaluating it independently for the lookup and the insertion.

   New in version 3.4.

PyObject *PyDict_Items(PyObject *p)
    *Return value: New reference.** Part of the Stable ABI.*

   Return a "PyListObject" containing all the items from the
   dictionary.

PyObject *PyDict_Keys(PyObject *p)
    *Return value: New reference.** Part of the Stable ABI.*

   Return a "PyListObject" containing all the keys from the
   dictionary.

PyObject *PyDict_Values(PyObject *p)
    *Return value: New reference.** Part of the Stable ABI.*

   Return a "PyListObject" containing all the values from the
   dictionary *p*.

Py_ssize_t PyDict_Size(PyObject *p)
    * Part of the Stable ABI.*

   Return the number of items in the dictionary.  This is equivalent
   to "len(p)" on a dictionary.

int PyDict_Next(PyObject *p, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue)
    * Part of the Stable ABI.*

   Iterate over all key-value pairs in the dictionary *p*.  The
   "Py_ssize_t" referred to by *ppos* must be initialized to "0" prior
   to the first call to this function to start the iteration; the
   function returns true for each pair in the dictionary, and false
   once all pairs have been reported.  The parameters *pkey* and
   *pvalue* should either point to PyObject* variables that will be
   filled in with each key and value, respectively, or may be "NULL".
   Any references returned through them are borrowed.  *ppos* should
   not be altered during iteration. Its value represents offsets
   within the internal dictionary structure, and since the structure
   is sparse, the offsets are not consecutive.

   For example:

      PyObject *key, *value;
      Py_ssize_t pos = 0;

      while (PyDict_Next(self->dict, &pos, &key, &value)) {
          /* do something interesting with the values... */
          ...
      }

   The dictionary *p* should not be mutated during iteration.  It is
   safe to modify the values of the keys as you iterate over the
   dictionary, but only so long as the set of keys does not change.
   For example:

      PyObject *key, *value;
      Py_ssize_t pos = 0;

      while (PyDict_Next(self->dict, &pos, &key, &value)) {
          long i = PyLong_AsLong(value);
          if (i == -1 && PyErr_Occurred()) {
              return -1;
          }
          PyObject *o = PyLong_FromLong(i + 1);
          if (o == NULL)
              return -1;
          if (PyDict_SetItem(self->dict, key, o) < 0) {
              Py_DECREF(o);
              return -1;
          }
          Py_DECREF(o);
      }

int PyDict_Merge(PyObject *a, PyObject *b, int override)
    * Part of the Stable ABI.*

   Iterate over mapping object *b* adding key-value pairs to
   dictionary *a*. *b* may be a dictionary, or any object supporting
   "PyMapping_Keys()" and "PyObject_GetItem()". If *override* is true,
   existing pairs in *a* will be replaced if a matching key is found
   in *b*, otherwise pairs will only be added if there is not a
   matching key in *a*. Return "0" on success or "-1" if an exception
   was raised.

int PyDict_Update(PyObject *a, PyObject *b)
    * Part of the Stable ABI.*

   This is the same as "PyDict_Merge(a, b, 1)" in C, and is similar to
   "a.update(b)" in Python except that "PyDict_Update()" doesn’t fall
   back to the iterating over a sequence of key value pairs if the
   second argument has no “keys” attribute.  Return "0" on success or
   "-1" if an exception was raised.

int PyDict_MergeFromSeq2(PyObject *a, PyObject *seq2, int override)
    * Part of the Stable ABI.*

   Update or merge into dictionary *a*, from the key-value pairs in
   *seq2*. *seq2* must be an iterable object producing iterable
   objects of length 2, viewed as key-value pairs.  In case of
   duplicate keys, the last wins if *override* is true, else the first
   wins. Return "0" on success or "-1" if an exception was raised.
   Equivalent Python (except for the return value):

      def PyDict_MergeFromSeq2(a, seq2, override):
          for key, value in seq2:
              if override or key not in a:
                  a[key] = value

int PyDict_AddWatcher(PyDict_WatchCallback callback)

   Register *callback* as a dictionary watcher. Return a non-negative
   integer id which must be passed to future calls to
   "PyDict_Watch()". In case of error (e.g. no more watcher IDs
   available), return "-1" and set an exception.

   New in version 3.12.

int PyDict_ClearWatcher(int watcher_id)

   Clear watcher identified by *watcher_id* previously returned from
   "PyDict_AddWatcher()". Return "0" on success, "-1" on error (e.g.
   if the given *watcher_id* was never registered.)

   New in version 3.12.

int PyDict_Watch(int watcher_id, PyObject *dict)

   Mark dictionary *dict* as watched. The callback granted
   *watcher_id* by "PyDict_AddWatcher()" will be called when *dict* is
   modified or deallocated. Return "0" on success or "-1" on error.

   New in version 3.12.

int PyDict_Unwatch(int watcher_id, PyObject *dict)

   Mark dictionary *dict* as no longer watched. The callback granted
   *watcher_id* by "PyDict_AddWatcher()" will no longer be called when
   *dict* is modified or deallocated. The dict must previously have
   been watched by this watcher. Return "0" on success or "-1" on
   error.

   New in version 3.12.

type PyDict_WatchEvent

   Enumeration of possible dictionary watcher events:
   "PyDict_EVENT_ADDED", "PyDict_EVENT_MODIFIED",
   "PyDict_EVENT_DELETED", "PyDict_EVENT_CLONED",
   "PyDict_EVENT_CLEARED", or "PyDict_EVENT_DEALLOCATED".

   New in version 3.12.

typedef int (*PyDict_WatchCallback)(PyDict_WatchEvent event, PyObject *dict, PyObject *key, PyObject *new_value)

   Type of a dict watcher callback function.

   If *event* is "PyDict_EVENT_CLEARED" or "PyDict_EVENT_DEALLOCATED",
   both *key* and *new_value* will be "NULL". If *event* is
   "PyDict_EVENT_ADDED" or "PyDict_EVENT_MODIFIED", *new_value* will
   be the new value for *key*. If *event* is "PyDict_EVENT_DELETED",
   *key* is being deleted from the dictionary and *new_value* will be
   "NULL".

   "PyDict_EVENT_CLONED" occurs when *dict* was previously empty and
   another dict is merged into it. To maintain efficiency of this
   operation, per-key "PyDict_EVENT_ADDED" events are not issued in
   this case; instead a single "PyDict_EVENT_CLONED" is issued, and
   *key* will be the source dictionary.

   The callback may inspect but must not modify *dict*; doing so could
   have unpredictable effects, including infinite recursion. Do not
   trigger Python code execution in the callback, as it could modify
   the dict as a side effect.

   If *event* is "PyDict_EVENT_DEALLOCATED", taking a new reference in
   the callback to the about-to-be-destroyed dictionary will resurrect
   it and prevent it from being freed at this time. When the
   resurrected object is destroyed later, any watcher callbacks active
   at that time will be called again.

   Callbacks occur before the notified modification to *dict* takes
   place, so the prior state of *dict* can be inspected.

   If the callback sets an exception, it must return "-1"; this
   exception will be printed as an unraisable exception using
   "PyErr_WriteUnraisable()". Otherwise it should return "0".

   There may already be a pending exception set on entry to the
   callback. In this case, the callback should return "0" with the
   same exception still set. This means the callback may not call any
   other API that can set an exception unless it saves and clears the
   exception state first, and restores it before returning.

   New in version 3.12.
