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.. highlightlang:: c
.. _dictobjects:
Dictionary Objects
------------------
.. index:: object: dictionary
.. c:type:: PyDictObject
This subtype of :c:type:`PyObject` represents a Python dictionary object.
.. c:var:: PyTypeObject PyDict_Type
This instance of :c:type:`PyTypeObject` represents the Python dictionary
type. This is the same object as :class:`dict` in the Python layer.
.. c:function:: int PyDict_Check(PyObject *p)
Return true if *p* is a dict object or an instance of a subtype of the dict
type.
.. c:function:: int PyDict_CheckExact(PyObject *p)
Return true if *p* is a dict object, but not an instance of a subtype of
the dict type.
.. c:function:: PyObject* PyDict_New()
Return a new empty dictionary, or *NULL* on failure.
.. c:function:: PyObject* PyDictProxy_New(PyObject *mapping)
Return a :class:`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.
.. c:function:: void PyDict_Clear(PyObject *p)
Empty an existing dictionary of all key-value pairs.
.. c:function:: 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``.
.. c:function:: PyObject* PyDict_Copy(PyObject *p)
Return a new dictionary that contains the same key-value pairs as *p*.
.. c:function:: int PyDict_SetItem(PyObject *p, PyObject *key, PyObject *val)
Insert *value* into the dictionary *p* with a key of *key*. *key* must be
:term:`hashable`; if it isn't, :exc:`TypeError` will be raised. Return
``0`` on success or ``-1`` on failure.
.. c:function:: int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)
.. index:: single: PyUnicode_FromString()
Insert *value* into the dictionary *p* using *key* as a key. *key* should
be a :c:type:`char\*`. The key object is created using
``PyUnicode_FromString(key)``. Return ``0`` on success or ``-1`` on
failure.
.. c:function:: int PyDict_DelItem(PyObject *p, PyObject *key)
Remove the entry in dictionary *p* with key *key*. *key* must be hashable;
if it isn't, :exc:`TypeError` is raised. Return ``0`` on success or ``-1``
on failure.
.. c:function:: int PyDict_DelItemString(PyObject *p, const char *key)
Remove the entry in dictionary *p* which has a key specified by the string
*key*. Return ``0`` on success or ``-1`` on failure.
.. c:function:: PyObject* PyDict_GetItem(PyObject *p, PyObject *key)
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.
.. c:function:: PyObject* PyDict_GetItemWithError(PyObject *p, PyObject *key)
Variant of :c:func:`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.
.. c:function:: PyObject* PyDict_GetItemString(PyObject *p, const char *key)
This is the same as :c:func:`PyDict_GetItem`, but *key* is specified as a
:c:type:`char\*`, rather than a :c:type:`PyObject\*`.
.. c:function:: PyObject* PyDict_SetDefault(PyObject *p, PyObject *key, PyObject *default)
This is the same as the Python-level :meth:`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.
.. versionadded:: 3.4
.. c:function:: PyObject* PyDict_Items(PyObject *p)
Return a :c:type:`PyListObject` containing all the items from the dictionary.
.. c:function:: PyObject* PyDict_Keys(PyObject *p)
Return a :c:type:`PyListObject` containing all the keys from the dictionary.
.. c:function:: PyObject* PyDict_Values(PyObject *p)
Return a :c:type:`PyListObject` containing all the values from the dictionary
*p*.
.. c:function:: Py_ssize_t PyDict_Size(PyObject *p)
.. index:: builtin: len
Return the number of items in the dictionary. This is equivalent to
``len(p)`` on a dictionary.
.. c:function:: int PyDict_Next(PyObject *p, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue)
Iterate over all key-value pairs in the dictionary *p*. The
:c:type:`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 :c:type:`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);
}
.. c:function:: 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 :c:func:`PyMapping_Keys`
and :c:func:`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.
.. c:function:: 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 :c:func:`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.
.. c:function:: 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
.. c:function:: int PyDict_ClearFreeList()
Clear the free list. Return the total number of freed items.
.. versionadded:: 3.3