Doc/c-api/dict.rst
.. highlight:: c
.. _dictobjects:
.. index:: pair: 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. This function always succeeds.
.. 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. This function always succeeds.
.. 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.
The first argument can be a :class:dict, a :class:frozendict, or a
mapping.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:var:: PyTypeObject PyDictProxy_Type
The type object for mapping proxy objects created by
:c:func:PyDictProxy_New and for the read-only __dict__ attribute
of many built-in types. A :c:type:PyDictProxy_Type instance provides a
dynamic, read-only view of an underlying dictionary: changes to the
underlying dictionary are reflected in the proxy, but the proxy itself
does not support mutation operations. This corresponds to
:class:types.MappingProxyType in Python.
.. c:function:: void PyDict_Clear(PyObject *p)
Empty an existing dictionary of all key-value pairs.
Do nothing if the argument is not a :class:dict or a :class:!dict
subclass.
.. c:function:: int PyDict_Contains(PyObject *p, PyObject *key)
Determine if dictionary p contains key. If an item in p matches
key, return 1, otherwise return 0. On error, return -1.
This is equivalent to the Python expression key in p.
The first argument can be a :class:dict or a :class:frozendict.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: int PyDict_ContainsString(PyObject *p, const char *key)
This is the same as :c:func:PyDict_Contains, but key is specified as a
:c:expr:const char* UTF-8 encoded bytes string, rather than a
:c:expr:PyObject*.
The first argument can be a :class:dict or a :class:frozendict.
.. versionadded:: 3.13
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. 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 val 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. This function does not steal a
reference to val.
.. c:function:: int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)
This is the same as :c:func:PyDict_SetItem, but key is
specified as a :c:expr:const char* UTF-8 encoded bytes string,
rather than a :c:expr:PyObject*.
.. c:function:: int PyDict_DelItem(PyObject *p, PyObject *key)
Remove the entry in dictionary p with key key. key must be :term:hashable;
if it isn't, :exc:TypeError is raised.
If key is not in the dictionary, :exc:KeyError is raised.
Return 0 on success or -1 on failure.
.. c:function:: int PyDict_DelItemString(PyObject *p, const char *key)
This is the same as :c:func:PyDict_DelItem, but key is
specified as a :c:expr:const char* UTF-8 encoded bytes string,
rather than a :c:expr:PyObject*.
.. c:function:: int PyDict_GetItemRef(PyObject *p, PyObject *key, PyObject **result)
Return a new :term:strong reference to the object from dictionary p
which has a key key:
strong reference
to the value and return 1.NULL and return 0.-1.The first argument can be a :class:dict or a :class:frozendict.
.. versionadded:: 3.13
.. versionchanged:: 3.15
Also accept :class:frozendict.
See also the :c:func:PyObject_GetItem function.
.. c:function:: PyObject* PyDict_GetItem(PyObject *p, PyObject *key)
Return a :term:borrowed reference to the object from dictionary p which
has a key key. Return NULL if the key key is missing without
setting an exception.
The first argument can be a :class:dict or a :class:frozendict.
.. note::
Exceptions that occur while this calls :meth:`~object.__hash__` and
:meth:`~object.__eq__` methods are silently ignored.
Prefer the :c:func:`PyDict_GetItemWithError` function instead.
.. versionchanged:: 3.10
Calling this API without an :term:attached thread state had been allowed for historical
reason. It is no longer allowed.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. 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.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. 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:expr:const char* UTF-8 encoded bytes string, rather than a
:c:expr:PyObject*.
.. note::
Exceptions that occur while this calls :meth:`~object.__hash__` and
:meth:`~object.__eq__` methods or while creating the temporary :class:`str`
object are silently ignored.
Prefer using the :c:func:`PyDict_GetItemWithError` function with your own
:c:func:`PyUnicode_FromString` *key* instead.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: int PyDict_GetItemStringRef(PyObject *p, const char *key, PyObject **result)
Similar to :c:func:PyDict_GetItemRef, but key is specified as a
:c:expr:const char* UTF-8 encoded bytes string, rather than a
:c:expr:PyObject*.
.. versionadded:: 3.13
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: PyObject* PyDict_SetDefault(PyObject *p, PyObject *key, PyObject *defaultobj)
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:: int PyDict_SetDefaultRef(PyObject *p, PyObject *key, PyObject *default_value, PyObject **result)
Inserts default_value into the dictionary p with a key of key if the
key is not already present in the dictionary. If result is not NULL,
then *result is set to a :term:strong reference to either
default_value, if the key was not present, or the existing value, if key
was already present in the dictionary.
Returns 1 if the key was present and default_value was not inserted,
or 0 if the key was not present and default_value was inserted.
On failure, returns -1, sets an exception, and sets *result
to NULL.
For clarity: if you have a strong reference to default_value before
calling this function, then after it returns, you hold a strong reference
to both default_value and *result (if it's not NULL).
These may refer to the same object: in that case you hold two separate
references to it.
.. versionadded:: 3.13
.. c:function:: int PyDict_Pop(PyObject *p, PyObject *key, PyObject **result)
Remove key from dictionary p and optionally return the removed value.
Do not raise :exc:KeyError if the key is missing.
NULL, and return 1.NULL if result is not
NULL, and return 0.-1.Similar to :meth:dict.pop, but without the default value and
not raising :exc:KeyError if the key is missing.
.. versionadded:: 3.13
.. c:function:: int PyDict_PopString(PyObject *p, const char *key, PyObject **result)
Similar to :c:func:PyDict_Pop, but key is specified as a
:c:expr:const char* UTF-8 encoded bytes string, rather than a
:c:expr:PyObject*.
.. versionadded:: 3.13
.. c:function:: PyObject* PyDict_Items(PyObject *p)
Return a :c:type:PyListObject containing all the items from the dictionary.
The first argument can be a :class:dict or a :class:frozendict.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: PyObject* PyDict_Keys(PyObject *p)
Return a :c:type:PyListObject containing all the keys from the dictionary.
The first argument can be a :class:dict or a :class:frozendict.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: PyObject* PyDict_Values(PyObject *p)
Return a :c:type:PyListObject containing all the values from the dictionary
p.
The first argument can be a :class:dict or a :class:frozendict.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: Py_ssize_t PyDict_Size(PyObject *p)
.. index:: pair: built-in function; len
Return the number of items in the dictionary. This is equivalent to
len(p) on a dictionary.
The argument can be a :class:dict or a :class:frozendict.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. c:function:: Py_ssize_t PyDict_GET_SIZE(PyObject *p)
Similar to :c:func:PyDict_Size, but without error checking.
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. 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:expr: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.
The first argument can be a :class:dict or a :class:frozendict.
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);
}
The function is not thread-safe in the :term:free-threaded <free threading>
build without external synchronization for a mutable :class:dict. You can use
:c:macro:Py_BEGIN_CRITICAL_SECTION to lock the dictionary while iterating
over it::
Py_BEGIN_CRITICAL_SECTION(self->dict);
while (PyDict_Next(self->dict, &pos, &key, &value)) {
...
}
Py_END_CRITICAL_SECTION();
The function is thread-safe on a :class:frozendict.
.. note::
On the free-threaded build, this function can be used safely inside a
critical section. However, the references returned for *pkey* and *pvalue*
are :term:`borrowed <borrowed reference>` and are only valid while the
critical section is held. If you need to use these objects outside the
critical section or when the critical section can be suspended, create a
:term:`strong reference <strong reference>` (for example, using
:c:func:`Py_NewRef`).
.. versionchanged:: 3.15
Also accept :class:frozendict.
.. 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_AddWatcher(PyDict_WatchCallback callback)
Register callback as a dictionary watcher. Return a non-negative integer
id which must be passed to future calls to :c:func:PyDict_Watch. In case
of error (e.g. no more watcher IDs available), return -1 and set an
exception.
.. versionadded:: 3.12
.. c:function:: int PyDict_ClearWatcher(int watcher_id)
Clear watcher identified by watcher_id previously returned from
:c:func:PyDict_AddWatcher. Return 0 on success, -1 on error (e.g.
if the given watcher_id was never registered.)
.. versionadded:: 3.12
.. c:function:: int PyDict_Watch(int watcher_id, PyObject *dict)
Mark dictionary dict as watched. The callback granted watcher_id by
:c:func:PyDict_AddWatcher will be called when dict is modified or
deallocated. Return 0 on success or -1 on error.
.. versionadded:: 3.12
.. c:function:: int PyDict_Unwatch(int watcher_id, PyObject *dict)
Mark dictionary dict as no longer watched. The callback granted
watcher_id by :c:func: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.
.. versionadded:: 3.12
.. c: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.
.. versionadded:: 3.12
.. c:type:: 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 :c:func: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.
.. versionadded:: 3.12
Dictionary view objects ^^^^^^^^^^^^^^^^^^^^^^^
.. c:function:: int PyDictViewSet_Check(PyObject *op)
Return true if op is a view of a set inside a dictionary. This is currently
equivalent to :c:expr:PyDictKeys_Check(op) || PyDictItems_Check(op). This
function always succeeds.
.. c:var:: PyTypeObject PyDictKeys_Type
Type object for a view of dictionary keys. In Python, this is the type of
the object returned by :meth:dict.keys.
.. c:function:: int PyDictKeys_Check(PyObject *op)
Return true if op is an instance of a dictionary keys view. This function always succeeds.
.. c:var:: PyTypeObject PyDictValues_Type
Type object for a view of dictionary values. In Python, this is the type of
the object returned by :meth:dict.values.
.. c:function:: int PyDictValues_Check(PyObject *op)
Return true if op is an instance of a dictionary values view. This function always succeeds.
.. c:var:: PyTypeObject PyDictItems_Type
Type object for a view of dictionary items. In Python, this is the type of
the object returned by :meth:dict.items.
.. c:function:: int PyDictItems_Check(PyObject *op)
Return true if op is an instance of a dictionary items view. This function always succeeds.
Frozen dictionary objects ^^^^^^^^^^^^^^^^^^^^^^^^^
.. versionadded:: 3.15
.. c:var:: PyTypeObject PyFrozenDict_Type
This instance of :c:type:PyTypeObject represents the Python frozen
dictionary type.
This is the same object as :class:frozendict in the Python layer.
.. c:function:: int PyAnyDict_Check(PyObject *p)
Return true if p is a :class:dict object, a :class:frozendict object,
or an instance of a subtype of the :class:!dict or :class:!frozendict
type.
This function always succeeds.
.. c:function:: int PyAnyDict_CheckExact(PyObject *p)
Return true if p is a :class:dict object or a :class:frozendict object,
but not an instance of a subtype of the :class:!dict or
:class:!frozendict type.
This function always succeeds.
.. c:function:: int PyFrozenDict_Check(PyObject *p)
Return true if p is a :class:frozendict object or an instance of a
subtype of the :class:!frozendict type.
This function always succeeds.
.. c:function:: int PyFrozenDict_CheckExact(PyObject *p)
Return true if p is a :class:frozendict object, but not an instance of a
subtype of the :class:!frozendict type.
This function always succeeds.
.. c:function:: PyObject* PyFrozenDict_New(PyObject *iterable)
Return a new :class:frozendict from an iterable, or NULL on failure
with an exception set.
Create an empty dictionary if iterable is NULL.
Ordered dictionaries ^^^^^^^^^^^^^^^^^^^^
Python's C API provides interface for :class:collections.OrderedDict from C.
Since Python 3.7, dictionaries are ordered by default, so there is usually
little need for these functions; prefer PyDict* where possible.
.. c:var:: PyTypeObject PyODict_Type
Type object for ordered dictionaries. This is the same object as
:class:collections.OrderedDict in the Python layer.
.. c:function:: int PyODict_Check(PyObject *od)
Return true if od is an ordered dictionary object or an instance of a
subtype of the :class:~collections.OrderedDict type. This function
always succeeds.
.. c:function:: int PyODict_CheckExact(PyObject *od)
Return true if od is an ordered dictionary object, but not an instance of
a subtype of the :class:~collections.OrderedDict type.
This function always succeeds.
.. c:var:: PyTypeObject PyODictKeys_Type
Analogous to :c:type:PyDictKeys_Type for ordered dictionaries.
.. c:var:: PyTypeObject PyODictValues_Type
Analogous to :c:type:PyDictValues_Type for ordered dictionaries.
.. c:var:: PyTypeObject PyODictItems_Type
Analogous to :c:type:PyDictItems_Type for ordered dictionaries.
.. c:function:: PyObject *PyODict_New(void)
Return a new empty ordered dictionary, or NULL on failure.
This is analogous to :c:func:PyDict_New.
.. c:function:: int PyODict_SetItem(PyObject *od, PyObject *key, PyObject *value)
Insert value into the ordered dictionary od with a key of key.
Return 0 on success or -1 with an exception set on failure.
This is analogous to :c:func:PyDict_SetItem.
.. c:function:: int PyODict_DelItem(PyObject *od, PyObject *key)
Remove the entry in the ordered dictionary od with key key.
Return 0 on success or -1 with an exception set on failure.
This is analogous to :c:func:PyDict_DelItem.
These are :term:soft deprecated aliases to PyDict APIs:
.. list-table:: :widths: auto :header-rows: 1
PyODictPyDictPyDict_GetItemPyDict_GetItemWithErrorPyDict_GetItemStringPyDict_ContainsPyDict_SizePyDict_GET_SIZE