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

PyDictObject

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

PyTypeObject PyDict_Type

   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.

int PyDict_CheckExact(PyObject *p)

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

PyObject* PyDict_New()
    *Return value: New reference.*

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

PyObject* PyDictProxy_New(PyObject *mapping)
    *Return value: New reference.*

   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)

   Empty an existing dictionary of all key-value pairs.

int PyDict_Contains(PyObject *p, PyObject *key)

   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.*

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

int PyDict_SetItem(PyObject *p, PyObject *key, PyObject *val)

   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)

   Insert *val* into the dictionary *p* using *key* as a key. *key*
   should be a "const char*".  The key object is created using
   "PyUnicode_FromString(key)".  Return "0" on success or "-1" on
   failure.  This function *does not* steal a reference to *val*.

int PyDict_DelItem(PyObject *p, PyObject *key)

   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)

   Remove the entry in dictionary *p* which has a key specified by the
   string *key*. If *key* is not in the dictionary, "KeyError" is
   raised. Return "0" on success or "-1" on failure.

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

   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 that exceptions which occur while calling "__hash__()" and
   "__eq__()" methods will get suppressed. To get error reporting use
   "PyDict_GetItemWithError()" instead.

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

   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.*

   This is the same as "PyDict_GetItem()", but *key* is specified as a
   "const char*", rather than a "PyObject*".

   Note that exceptions which occur while calling "__hash__()" and
   "__eq__()" methods and creating a temporary string object will get
   suppressed. To get error reporting use "PyDict_GetItemWithError()"
   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.*

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

PyObject* PyDict_Keys(PyObject *p)
    *Return value: New reference.*

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

PyObject* PyDict_Values(PyObject *p)
    *Return value: New reference.*

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

Py_ssize_t PyDict_Size(PyObject *p)

   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)

   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)

   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)

   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)

   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
