234 lines
7.4 KiB
ReStructuredText
234 lines
7.4 KiB
ReStructuredText
.. highlightlang:: c
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.. _dictobjects:
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Dictionary Objects
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------------------
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.. index:: object: dictionary
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.. ctype:: PyDictObject
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This subtype of :ctype:`PyObject` represents a Python dictionary object.
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.. cvar:: PyTypeObject PyDict_Type
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.. index::
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single: DictType (in module types)
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single: DictionaryType (in module types)
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This instance of :ctype:`PyTypeObject` represents the Python dictionary
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type. This is exposed to Python programs as ``dict`` and
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``types.DictType``.
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.. cfunction:: int PyDict_Check(PyObject *p)
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Return true if *p* is a dict object or an instance of a subtype of the dict
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type.
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.. versionchanged:: 2.2
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Allowed subtypes to be accepted.
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.. cfunction:: int PyDict_CheckExact(PyObject *p)
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Return true if *p* is a dict object, but not an instance of a subtype of
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the dict type.
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.. versionadded:: 2.4
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.. cfunction:: PyObject* PyDict_New()
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Return a new empty dictionary, or *NULL* on failure.
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.. cfunction:: PyObject* PyDictProxy_New(PyObject *dict)
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Return a proxy object for a mapping which enforces read-only behavior.
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This is normally used to create a proxy to prevent modification of the
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dictionary for non-dynamic class types.
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.. versionadded:: 2.2
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.. cfunction:: void PyDict_Clear(PyObject *p)
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Empty an existing dictionary of all key-value pairs.
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.. cfunction:: int PyDict_Contains(PyObject *p, PyObject *key)
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Determine if dictionary *p* contains *key*. If an item in *p* is matches
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*key*, return ``1``, otherwise return ``0``. On error, return ``-1``.
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This is equivalent to the Python expression ``key in p``.
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.. versionadded:: 2.4
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.. cfunction:: PyObject* PyDict_Copy(PyObject *p)
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Return a new dictionary that contains the same key-value pairs as *p*.
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.. versionadded:: 1.6
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.. cfunction:: int PyDict_SetItem(PyObject *p, PyObject *key, PyObject *val)
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Insert *value* into the dictionary *p* with a key of *key*. *key* must be
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:term:`hashable`; if it isn't, :exc:`TypeError` will be raised. Return
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``0`` on success or ``-1`` on failure.
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.. cfunction:: int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)
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.. index:: single: PyString_FromString()
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Insert *value* into the dictionary *p* using *key* as a key. *key* should
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be a :ctype:`char\*`. The key object is created using
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``PyString_FromString(key)``. Return ``0`` on success or ``-1`` on
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failure.
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.. cfunction:: int PyDict_DelItem(PyObject *p, PyObject *key)
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Remove the entry in dictionary *p* with key *key*. *key* must be hashable;
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if it isn't, :exc:`TypeError` is raised. Return ``0`` on success or ``-1``
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on failure.
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.. cfunction:: int PyDict_DelItemString(PyObject *p, char *key)
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Remove the entry in dictionary *p* which has a key specified by the string
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*key*. Return ``0`` on success or ``-1`` on failure.
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.. cfunction:: PyObject* PyDict_GetItem(PyObject *p, PyObject *key)
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Return the object from dictionary *p* which has a key *key*. Return *NULL*
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if the key *key* is not present, but *without* setting an exception.
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.. cfunction:: PyObject* PyDict_GetItemString(PyObject *p, const char *key)
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This is the same as :cfunc:`PyDict_GetItem`, but *key* is specified as a
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:ctype:`char\*`, rather than a :ctype:`PyObject\*`.
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.. cfunction:: PyObject* PyDict_Items(PyObject *p)
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Return a :ctype:`PyListObject` containing all the items from the
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dictionary, as in the dictionary method :meth:`dict.items`.
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.. cfunction:: PyObject* PyDict_Keys(PyObject *p)
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Return a :ctype:`PyListObject` containing all the keys from the dictionary,
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as in the dictionary method :meth:`dict.keys`.
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.. cfunction:: PyObject* PyDict_Values(PyObject *p)
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Return a :ctype:`PyListObject` containing all the values from the
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dictionary *p*, as in the dictionary method :meth:`dict.values`.
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.. cfunction:: Py_ssize_t PyDict_Size(PyObject *p)
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.. index:: builtin: len
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Return the number of items in the dictionary. This is equivalent to
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``len(p)`` on a dictionary.
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.. versionchanged:: 2.5
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This function returned an :ctype:`int` type. This might require changes
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in your code for properly supporting 64-bit systems.
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.. cfunction:: int PyDict_Next(PyObject *p, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue)
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Iterate over all key-value pairs in the dictionary *p*. The
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:ctype:`Py_ssize_t` referred to by *ppos* must be initialized to ``0``
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prior to the first call to this function to start the iteration; the
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function returns true for each pair in the dictionary, and false once all
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pairs have been reported. The parameters *pkey* and *pvalue* should either
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point to :ctype:`PyObject\*` variables that will be filled in with each key
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and value, respectively, or may be *NULL*. Any references returned through
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them are borrowed. *ppos* should not be altered during iteration. Its
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value represents offsets within the internal dictionary structure, and
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since the structure is sparse, the offsets are not consecutive.
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For example::
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PyObject *key, *value;
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Py_ssize_t pos = 0;
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while (PyDict_Next(self->dict, &pos, &key, &value)) {
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/* do something interesting with the values... */
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...
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}
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The dictionary *p* should not be mutated during iteration. It is safe
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(since Python 2.1) to modify the values of the keys as you iterate over the
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dictionary, but only so long as the set of keys does not change. For
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example::
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PyObject *key, *value;
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Py_ssize_t pos = 0;
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while (PyDict_Next(self->dict, &pos, &key, &value)) {
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int i = PyInt_AS_LONG(value) + 1;
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PyObject *o = PyInt_FromLong(i);
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if (o == NULL)
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return -1;
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if (PyDict_SetItem(self->dict, key, o) < 0) {
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Py_DECREF(o);
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return -1;
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}
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Py_DECREF(o);
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}
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.. versionchanged:: 2.5
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This function used an :ctype:`int *` type for *ppos*. This might require
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changes in your code for properly supporting 64-bit systems.
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.. cfunction:: int PyDict_Merge(PyObject *a, PyObject *b, int override)
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Iterate over mapping object *b* adding key-value pairs to dictionary *a*.
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*b* may be a dictionary, or any object supporting :func:`PyMapping_Keys`
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and :func:`PyObject_GetItem`. If *override* is true, existing pairs in *a*
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will be replaced if a matching key is found in *b*, otherwise pairs will
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only be added if there is not a matching key in *a*. Return ``0`` on
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success or ``-1`` if an exception was raised.
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.. versionadded:: 2.2
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.. cfunction:: int PyDict_Update(PyObject *a, PyObject *b)
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This is the same as ``PyDict_Merge(a, b, 1)`` in C, or ``a.update(b)`` in
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Python. Return ``0`` on success or ``-1`` if an exception was raised.
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.. versionadded:: 2.2
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.. cfunction:: int PyDict_MergeFromSeq2(PyObject *a, PyObject *seq2, int override)
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Update or merge into dictionary *a*, from the key-value pairs in *seq2*.
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*seq2* must be an iterable object producing iterable objects of length 2,
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viewed as key-value pairs. In case of duplicate keys, the last wins if
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*override* is true, else the first wins. Return ``0`` on success or ``-1``
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if an exception was raised. Equivalent Python (except for the return
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value)::
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def PyDict_MergeFromSeq2(a, seq2, override):
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for key, value in seq2:
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if override or key not in a:
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a[key] = value
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.. versionadded:: 2.2
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