Python 3.6.5 Documentation >  Dictionary Objects

Dictionary Objects
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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 *value* 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.

int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)

Insert *value* into the dictionary *p* using *key* as a key. *key*
should be a "char*". The key object is created using
"PyUnicode_FromString(key)". Return "0" on success or "-1" on
failure.

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. 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*. 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.

PyObject* PyDict_GetItemWithError(PyObject *p, PyObject *key)

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
"char*", rather than a "PyObject*".

PyObject* PyDict_SetDefault(PyObject *p, PyObject *key, PyObject *default)
*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

int PyDict_ClearFreeList()

Clear the free list. Return the total number of freed items.

New in version 3.3.