/Doc/c-api/string.rst

  1.. highlightlang:: c
  2
  3.. _stringobjects:
  4
  5String/Bytes Objects
  6--------------------
  7
  8These functions raise :exc:`TypeError` when expecting a string parameter and are
  9called with a non-string parameter.
 10
 11.. note::
 12   These functions have been renamed to PyBytes_* in Python 3.x. The PyBytes
 13   names are also available in 2.6.
 14
 15.. index:: object: string
 16
 17
 18.. ctype:: PyStringObject
 19
 20   This subtype of :ctype:`PyObject` represents a Python string object.
 21
 22
 23.. cvar:: PyTypeObject PyString_Type
 24
 25   .. index:: single: StringType (in module types)
 26
 27   This instance of :ctype:`PyTypeObject` represents the Python string type; it is
 28   the same object as ``str`` and ``types.StringType`` in the Python layer. .
 29
 30
 31.. cfunction:: int PyString_Check(PyObject *o)
 32
 33   Return true if the object *o* is a string object or an instance of a subtype of
 34   the string type.
 35
 36   .. versionchanged:: 2.2
 37      Allowed subtypes to be accepted.
 38
 39
 40.. cfunction:: int PyString_CheckExact(PyObject *o)
 41
 42   Return true if the object *o* is a string object, but not an instance of a
 43   subtype of the string type.
 44
 45   .. versionadded:: 2.2
 46
 47
 48.. cfunction:: PyObject* PyString_FromString(const char *v)
 49
 50   Return a new string object with a copy of the string *v* as value on success,
 51   and *NULL* on failure.  The parameter *v* must not be *NULL*; it will not be
 52   checked.
 53
 54
 55.. cfunction:: PyObject* PyString_FromStringAndSize(const char *v, Py_ssize_t len)
 56
 57   Return a new string object with a copy of the string *v* as value and length
 58   *len* on success, and *NULL* on failure.  If *v* is *NULL*, the contents of the
 59   string are uninitialized.
 60
 61   .. versionchanged:: 2.5
 62      This function used an :ctype:`int` type for *len*. This might require
 63      changes in your code for properly supporting 64-bit systems.
 64
 65
 66.. cfunction:: PyObject* PyString_FromFormat(const char *format, ...)
 67
 68   Take a C :cfunc:`printf`\ -style *format* string and a variable number of
 69   arguments, calculate the size of the resulting Python string and return a string
 70   with the values formatted into it.  The variable arguments must be C types and
 71   must correspond exactly to the format characters in the *format* string.  The
 72   following format characters are allowed:
 73
 74   .. % This should be exactly the same as the table in PyErr_Format.
 75   .. % One should just refer to the other.
 76   .. % The descriptions for %zd and %zu are wrong, but the truth is complicated
 77   .. % because not all compilers support the %z width modifier -- we fake it
 78   .. % when necessary via interpolating PY_FORMAT_SIZE_T.
 79   .. % %u, %lu, %zu should have "new in Python 2.5" blurbs.
 80
 81   +-------------------+---------------+--------------------------------+
 82   | Format Characters | Type          | Comment                        |
 83   +===================+===============+================================+
 84   | :attr:`%%`        | *n/a*         | The literal % character.       |
 85   +-------------------+---------------+--------------------------------+
 86   | :attr:`%c`        | int           | A single character,            |
 87   |                   |               | represented as an C int.       |
 88   +-------------------+---------------+--------------------------------+
 89   | :attr:`%d`        | int           | Exactly equivalent to          |
 90   |                   |               | ``printf("%d")``.              |
 91   +-------------------+---------------+--------------------------------+
 92   | :attr:`%u`        | unsigned int  | Exactly equivalent to          |
 93   |                   |               | ``printf("%u")``.              |
 94   +-------------------+---------------+--------------------------------+
 95   | :attr:`%ld`       | long          | Exactly equivalent to          |
 96   |                   |               | ``printf("%ld")``.             |
 97   +-------------------+---------------+--------------------------------+
 98   | :attr:`%lu`       | unsigned long | Exactly equivalent to          |
 99   |                   |               | ``printf("%lu")``.             |
100   +-------------------+---------------+--------------------------------+
101   | :attr:`%zd`       | Py_ssize_t    | Exactly equivalent to          |
102   |                   |               | ``printf("%zd")``.             |
103   +-------------------+---------------+--------------------------------+
104   | :attr:`%zu`       | size_t        | Exactly equivalent to          |
105   |                   |               | ``printf("%zu")``.             |
106   +-------------------+---------------+--------------------------------+
107   | :attr:`%i`        | int           | Exactly equivalent to          |
108   |                   |               | ``printf("%i")``.              |
109   +-------------------+---------------+--------------------------------+
110   | :attr:`%x`        | int           | Exactly equivalent to          |
111   |                   |               | ``printf("%x")``.              |
112   +-------------------+---------------+--------------------------------+
113   | :attr:`%s`        | char\*        | A null-terminated C character  |
114   |                   |               | array.                         |
115   +-------------------+---------------+--------------------------------+
116   | :attr:`%p`        | void\*        | The hex representation of a C  |
117   |                   |               | pointer. Mostly equivalent to  |
118   |                   |               | ``printf("%p")`` except that   |
119   |                   |               | it is guaranteed to start with |
120   |                   |               | the literal ``0x`` regardless  |
121   |                   |               | of what the platform's         |
122   |                   |               | ``printf`` yields.             |
123   +-------------------+---------------+--------------------------------+
124
125   An unrecognized format character causes all the rest of the format string to be
126   copied as-is to the result string, and any extra arguments discarded.
127
128
129.. cfunction:: PyObject* PyString_FromFormatV(const char *format, va_list vargs)
130
131   Identical to :cfunc:`PyString_FromFormat` except that it takes exactly two
132   arguments.
133
134
135.. cfunction:: Py_ssize_t PyString_Size(PyObject *string)
136
137   Return the length of the string in string object *string*.
138
139   .. versionchanged:: 2.5
140      This function returned an :ctype:`int` type. This might require changes
141      in your code for properly supporting 64-bit systems.
142
143
144.. cfunction:: Py_ssize_t PyString_GET_SIZE(PyObject *string)
145
146   Macro form of :cfunc:`PyString_Size` but without error checking.
147
148   .. versionchanged:: 2.5
149      This macro returned an :ctype:`int` type. This might require changes in
150      your code for properly supporting 64-bit systems.
151
152
153.. cfunction:: char* PyString_AsString(PyObject *string)
154
155   Return a NUL-terminated representation of the contents of *string*.  The pointer
156   refers to the internal buffer of *string*, not a copy.  The data must not be
157   modified in any way, unless the string was just created using
158   ``PyString_FromStringAndSize(NULL, size)``. It must not be deallocated.  If
159   *string* is a Unicode object, this function computes the default encoding of
160   *string* and operates on that.  If *string* is not a string object at all,
161   :cfunc:`PyString_AsString` returns *NULL* and raises :exc:`TypeError`.
162
163
164.. cfunction:: char* PyString_AS_STRING(PyObject *string)
165
166   Macro form of :cfunc:`PyString_AsString` but without error checking.  Only
167   string objects are supported; no Unicode objects should be passed.
168
169
170.. cfunction:: int PyString_AsStringAndSize(PyObject *obj, char **buffer, Py_ssize_t *length)
171
172   Return a NUL-terminated representation of the contents of the object *obj*
173   through the output variables *buffer* and *length*.
174
175   The function accepts both string and Unicode objects as input. For Unicode
176   objects it returns the default encoded version of the object.  If *length* is
177   *NULL*, the resulting buffer may not contain NUL characters; if it does, the
178   function returns ``-1`` and a :exc:`TypeError` is raised.
179
180   The buffer refers to an internal string buffer of *obj*, not a copy. The data
181   must not be modified in any way, unless the string was just created using
182   ``PyString_FromStringAndSize(NULL, size)``.  It must not be deallocated.  If
183   *string* is a Unicode object, this function computes the default encoding of
184   *string* and operates on that.  If *string* is not a string object at all,
185   :cfunc:`PyString_AsStringAndSize` returns ``-1`` and raises :exc:`TypeError`.
186
187   .. versionchanged:: 2.5
188      This function used an :ctype:`int *` type for *length*. This might
189      require changes in your code for properly supporting 64-bit systems.
190
191
192.. cfunction:: void PyString_Concat(PyObject **string, PyObject *newpart)
193
194   Create a new string object in *\*string* containing the contents of *newpart*
195   appended to *string*; the caller will own the new reference.  The reference to
196   the old value of *string* will be stolen.  If the new string cannot be created,
197   the old reference to *string* will still be discarded and the value of
198   *\*string* will be set to *NULL*; the appropriate exception will be set.
199
200
201.. cfunction:: void PyString_ConcatAndDel(PyObject **string, PyObject *newpart)
202
203   Create a new string object in *\*string* containing the contents of *newpart*
204   appended to *string*.  This version decrements the reference count of *newpart*.
205
206
207.. cfunction:: int _PyString_Resize(PyObject **string, Py_ssize_t newsize)
208
209   A way to resize a string object even though it is "immutable". Only use this to
210   build up a brand new string object; don't use this if the string may already be
211   known in other parts of the code.  It is an error to call this function if the
212   refcount on the input string object is not one. Pass the address of an existing
213   string object as an lvalue (it may be written into), and the new size desired.
214   On success, *\*string* holds the resized string object and ``0`` is returned;
215   the address in *\*string* may differ from its input value.  If the reallocation
216   fails, the original string object at *\*string* is deallocated, *\*string* is
217   set to *NULL*, a memory exception is set, and ``-1`` is returned.
218
219   .. versionchanged:: 2.5
220      This function used an :ctype:`int` type for *newsize*. This might
221      require changes in your code for properly supporting 64-bit systems.
222
223.. cfunction:: PyObject* PyString_Format(PyObject *format, PyObject *args)
224
225   Return a new string object from *format* and *args*. Analogous to ``format %
226   args``.  The *args* argument must be a tuple.
227
228
229.. cfunction:: void PyString_InternInPlace(PyObject **string)
230
231   Intern the argument *\*string* in place.  The argument must be the address of a
232   pointer variable pointing to a Python string object.  If there is an existing
233   interned string that is the same as *\*string*, it sets *\*string* to it
234   (decrementing the reference count of the old string object and incrementing the
235   reference count of the interned string object), otherwise it leaves *\*string*
236   alone and interns it (incrementing its reference count).  (Clarification: even
237   though there is a lot of talk about reference counts, think of this function as
238   reference-count-neutral; you own the object after the call if and only if you
239   owned it before the call.)
240
241
242.. cfunction:: PyObject* PyString_InternFromString(const char *v)
243
244   A combination of :cfunc:`PyString_FromString` and
245   :cfunc:`PyString_InternInPlace`, returning either a new string object that has
246   been interned, or a new ("owned") reference to an earlier interned string object
247   with the same value.
248
249
250.. cfunction:: PyObject* PyString_Decode(const char *s, Py_ssize_t size, const char *encoding, const char *errors)
251
252   Create an object by decoding *size* bytes of the encoded buffer *s* using the
253   codec registered for *encoding*.  *encoding* and *errors* have the same meaning
254   as the parameters of the same name in the :func:`unicode` built-in function.
255   The codec to be used is looked up using the Python codec registry.  Return
256   *NULL* if an exception was raised by the codec.
257
258   .. versionchanged:: 2.5
259      This function used an :ctype:`int` type for *size*. This might require
260      changes in your code for properly supporting 64-bit systems.
261
262
263.. cfunction:: PyObject* PyString_AsDecodedObject(PyObject *str, const char *encoding, const char *errors)
264
265   Decode a string object by passing it to the codec registered for *encoding* and
266   return the result as Python object. *encoding* and *errors* have the same
267   meaning as the parameters of the same name in the string :meth:`encode` method.
268   The codec to be used is looked up using the Python codec registry. Return *NULL*
269   if an exception was raised by the codec.
270
271
272.. cfunction:: PyObject* PyString_Encode(const char *s, Py_ssize_t size, const char *encoding, const char *errors)
273
274   Encode the :ctype:`char` buffer of the given size by passing it to the codec
275   registered for *encoding* and return a Python object. *encoding* and *errors*
276   have the same meaning as the parameters of the same name in the string
277   :meth:`encode` method. The codec to be used is looked up using the Python codec
278   registry.  Return *NULL* if an exception was raised by the codec.
279
280   .. versionchanged:: 2.5
281      This function used an :ctype:`int` type for *size*. This might require
282      changes in your code for properly supporting 64-bit systems.
283
284
285.. cfunction:: PyObject* PyString_AsEncodedObject(PyObject *str, const char *encoding, const char *errors)
286
287   Encode a string object using the codec registered for *encoding* and return the
288   result as Python object. *encoding* and *errors* have the same meaning as the
289   parameters of the same name in the string :meth:`encode` method. The codec to be
290   used is looked up using the Python codec registry. Return *NULL* if an exception
291   was raised by the codec.