2 :mod:`array` --- Efficient arrays of numeric values
3 ===================================================
6 :synopsis: Efficient arrays of uniformly typed numeric values.
9 .. index:: single: arrays
11 This module defines an object type which can efficiently represent an array of
12 basic values: characters, integers, floating point numbers. Arrays are sequence
13 types and behave very much like lists, except that the type of objects stored in
14 them is constrained. The type is specified at object creation time by using a
15 :dfn:`type code`, which is a single character. The following type codes are
18 +-----------+----------------+-------------------+-----------------------+
19 | Type code | C Type | Python Type | Minimum size in bytes |
20 +===========+================+===================+=======================+
21 | ``'c'`` | char | character | 1 |
22 +-----------+----------------+-------------------+-----------------------+
23 | ``'b'`` | signed char | int | 1 |
24 +-----------+----------------+-------------------+-----------------------+
25 | ``'B'`` | unsigned char | int | 1 |
26 +-----------+----------------+-------------------+-----------------------+
27 | ``'u'`` | Py_UNICODE | Unicode character | 2 |
28 +-----------+----------------+-------------------+-----------------------+
29 | ``'h'`` | signed short | int | 2 |
30 +-----------+----------------+-------------------+-----------------------+
31 | ``'H'`` | unsigned short | int | 2 |
32 +-----------+----------------+-------------------+-----------------------+
33 | ``'i'`` | signed int | int | 2 |
34 +-----------+----------------+-------------------+-----------------------+
35 | ``'I'`` | unsigned int | long | 2 |
36 +-----------+----------------+-------------------+-----------------------+
37 | ``'l'`` | signed long | int | 4 |
38 +-----------+----------------+-------------------+-----------------------+
39 | ``'L'`` | unsigned long | long | 4 |
40 +-----------+----------------+-------------------+-----------------------+
41 | ``'f'`` | float | float | 4 |
42 +-----------+----------------+-------------------+-----------------------+
43 | ``'d'`` | double | float | 8 |
44 +-----------+----------------+-------------------+-----------------------+
46 The actual representation of values is determined by the machine architecture
47 (strictly speaking, by the C implementation). The actual size can be accessed
48 through the :attr:`itemsize` attribute. The values stored for ``'L'`` and
49 ``'I'`` items will be represented as Python long integers when retrieved,
50 because Python's plain integer type cannot represent the full range of C's
51 unsigned (long) integers.
53 The module defines the following type:
56 .. function:: array(typecode[, initializer])
58 Return a new array whose items are restricted by *typecode*, and initialized
59 from the optional *initializer* value, which must be a list, string, or iterable
60 over elements of the appropriate type.
62 .. versionchanged:: 2.4
63 Formerly, only lists or strings were accepted.
65 If given a list or string, the initializer is passed to the new array's
66 :meth:`fromlist`, :meth:`fromstring`, or :meth:`fromunicode` method (see below)
67 to add initial items to the array. Otherwise, the iterable initializer is
68 passed to the :meth:`extend` method.
73 Obsolete alias for :func:`array`.
75 Array objects support the ordinary sequence operations of indexing, slicing,
76 concatenation, and multiplication. When using slice assignment, the assigned
77 value must be an array object with the same type code; in all other cases,
78 :exc:`TypeError` is raised. Array objects also implement the buffer interface,
79 and may be used wherever buffer objects are supported.
81 The following data items and methods are also supported:
84 .. attribute:: array.typecode
86 The typecode character used to create the array.
89 .. attribute:: array.itemsize
91 The length in bytes of one array item in the internal representation.
94 .. method:: array.append(x)
96 Append a new item with value *x* to the end of the array.
99 .. method:: array.buffer_info()
101 Return a tuple ``(address, length)`` giving the current memory address and the
102 length in elements of the buffer used to hold array's contents. The size of the
103 memory buffer in bytes can be computed as ``array.buffer_info()[1] *
104 array.itemsize``. This is occasionally useful when working with low-level (and
105 inherently unsafe) I/O interfaces that require memory addresses, such as certain
106 :cfunc:`ioctl` operations. The returned numbers are valid as long as the array
107 exists and no length-changing operations are applied to it.
111 When using array objects from code written in C or C++ (the only way to
112 effectively make use of this information), it makes more sense to use the buffer
113 interface supported by array objects. This method is maintained for backward
114 compatibility and should be avoided in new code. The buffer interface is
115 documented in :ref:`bufferobjects`.
118 .. method:: array.byteswap()
120 "Byteswap" all items of the array. This is only supported for values which are
121 1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is
122 raised. It is useful when reading data from a file written on a machine with a
123 different byte order.
126 .. method:: array.count(x)
128 Return the number of occurrences of *x* in the array.
131 .. method:: array.extend(iterable)
133 Append items from *iterable* to the end of the array. If *iterable* is another
134 array, it must have *exactly* the same type code; if not, :exc:`TypeError` will
135 be raised. If *iterable* is not an array, it must be iterable and its elements
136 must be the right type to be appended to the array.
138 .. versionchanged:: 2.4
139 Formerly, the argument could only be another array.
142 .. method:: array.fromfile(f, n)
144 Read *n* items (as machine values) from the file object *f* and append them to
145 the end of the array. If less than *n* items are available, :exc:`EOFError` is
146 raised, but the items that were available are still inserted into the array.
147 *f* must be a real built-in file object; something else with a :meth:`read`
151 .. method:: array.fromlist(list)
153 Append items from the list. This is equivalent to ``for x in list:
154 a.append(x)`` except that if there is a type error, the array is unchanged.
157 .. method:: array.fromstring(s)
159 Appends items from the string, interpreting the string as an array of machine
160 values (as if it had been read from a file using the :meth:`fromfile` method).
163 .. method:: array.fromunicode(s)
165 Extends this array with data from the given unicode string. The array must
166 be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised. Use
167 ``array.fromstring(unicodestring.encode(enc))`` to append Unicode data to an
168 array of some other type.
171 .. method:: array.index(x)
173 Return the smallest *i* such that *i* is the index of the first occurrence of
177 .. method:: array.insert(i, x)
179 Insert a new item with value *x* in the array before position *i*. Negative
180 values are treated as being relative to the end of the array.
183 .. method:: array.pop([i])
185 Removes the item with the index *i* from the array and returns it. The optional
186 argument defaults to ``-1``, so that by default the last item is removed and
190 .. method:: array.read(f, n)
192 .. deprecated:: 1.5.1
193 Use the :meth:`fromfile` method.
195 Read *n* items (as machine values) from the file object *f* and append them to
196 the end of the array. If less than *n* items are available, :exc:`EOFError` is
197 raised, but the items that were available are still inserted into the array.
198 *f* must be a real built-in file object; something else with a :meth:`read`
202 .. method:: array.remove(x)
204 Remove the first occurrence of *x* from the array.
207 .. method:: array.reverse()
209 Reverse the order of the items in the array.
212 .. method:: array.tofile(f)
214 Write all items (as machine values) to the file object *f*.
217 .. method:: array.tolist()
219 Convert the array to an ordinary list with the same items.
222 .. method:: array.tostring()
224 Convert the array to an array of machine values and return the string
225 representation (the same sequence of bytes that would be written to a file by
226 the :meth:`tofile` method.)
229 .. method:: array.tounicode()
231 Convert the array to a unicode string. The array must be a type ``'u'`` array;
232 otherwise a :exc:`ValueError` is raised. Use ``array.tostring().decode(enc)`` to
233 obtain a unicode string from an array of some other type.
236 .. method:: array.write(f)
238 .. deprecated:: 1.5.1
239 Use the :meth:`tofile` method.
241 Write all items (as machine values) to the file object *f*.
243 When an array object is printed or converted to a string, it is represented as
244 ``array(typecode, initializer)``. The *initializer* is omitted if the array is
245 empty, otherwise it is a string if the *typecode* is ``'c'``, otherwise it is a
246 list of numbers. The string is guaranteed to be able to be converted back to an
247 array with the same type and value using :func:`eval`, so long as the
248 :func:`array` function has been imported using ``from array import array``.
252 array('c', 'hello world')
253 array('u', u'hello \u2641')
254 array('l', [1, 2, 3, 4, 5])
255 array('d', [1.0, 2.0, 3.14])
261 Packing and unpacking of heterogeneous binary data.
264 Packing and unpacking of External Data Representation (XDR) data as used in some
265 remote procedure call systems.
267 `The Numerical Python Manual <http://numpy.sourceforge.net/numdoc/HTML/numdoc.htm>`_
268 The Numeric Python extension (NumPy) defines another array type; see
269 http://numpy.sourceforge.net/ for further information about Numerical Python.
270 (A PDF version of the NumPy manual is available at
271 http://numpy.sourceforge.net/numdoc/numdoc.pdf).