Dictionary Objects — Python 3.13.2 documentation

# 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`.

int PyDict_ContainsString(PyObject *p, const char *key)

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

  Added in version 3.13.

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*.

int PyDict_GetItemRef(PyObject *p, PyObject *key, PyObject **result)
  Part of the Stable ABI since version 3.13.

  Return a new strong reference to the object from dictionary p which has a key key:

  - If the key is present, set *result to a new strong reference to the value and return `1`.

  - If the key is missing, set *result to `NULL` and return `0`.

  - On error, raise an exception and return `-1`.

  Added in version 3.13.

  See also the `PyObject_GetItem()` function.

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

  Return a 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.

  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.

int PyDict_GetItemStringRef(PyObject *p, const char *key, PyObject **result)
  Part of the Stable ABI since version 3.13.

  Similar than `PyDict_GetItemRef()`, but key is specified as a const char* UTF-8 encoded bytes string, rather than a PyObject*.

  Added in version 3.13.

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.

  Added in version 3.4.

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 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.

  Added in version 3.13.

int PyDict_Pop(PyObject *p, PyObject *key, PyObject **result)

  Remove key from dictionary p and optionally return the removed value. Do not raise `KeyError` if the key missing.

  - If the key is present, set *result to a new reference to the removed value if result is not `NULL`, and return `1`.

  - If the key is missing, set *result to `NULL` if result is not `NULL`, and return `0`.

  - On error, raise an exception and return `-1`.

  This is similar to `dict.pop()`, but without the default value and not raising `KeyError` if the key missing.

  Added in version 3.13.

int PyDict_PopString(PyObject *p, const char *key, PyObject **result)

  Similar to `PyDict_Pop()`, but key is specified as a const char* UTF-8 encoded bytes string, rather than a PyObject*.

  Added in version 3.13.

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);
      }

  The function is not thread-safe in the free-threaded build without external synchronization. You can use `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();

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.

  Added 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.)

  Added 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.

  Added 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.

  Added 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`.

  Added 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.

  Added in version 3.12.