2 :mod:`array` --- Efficient arrays of numeric values
3 ===================================================
6 :synopsis: Space efficient arrays of uniformly typed numeric values.
9 .. index:: single: arrays
11 This module defines an object type which can compactly 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 (see note) |
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 +-----------+----------------+-------------------+-----------------------+
48 The ``'u'`` typecode corresponds to Python's unicode character. On narrow
49 Unicode builds this is 2-bytes, on wide builds this is 4-bytes.
51 The actual representation of values is determined by the machine architecture
52 (strictly speaking, by the C implementation). The actual size can be accessed
53 through the :attr:`itemsize` attribute. The values stored for ``'L'`` and
54 ``'I'`` items will be represented as Python long integers when retrieved,
55 because Python's plain integer type cannot represent the full range of C's
56 unsigned (long) integers.
58 The module defines the following type:
61 .. class:: array(typecode[, initializer])
63 A new array whose items are restricted by *typecode*, and initialized
64 from the optional *initializer* value, which must be a list, string, or iterable
65 over elements of the appropriate type.
67 .. versionchanged:: 2.4
68 Formerly, only lists or strings were accepted.
70 If given a list or string, the initializer is passed to the new array's
71 :meth:`fromlist`, :meth:`fromstring`, or :meth:`fromunicode` method (see below)
72 to add initial items to the array. Otherwise, the iterable initializer is
73 passed to the :meth:`extend` method.
78 Obsolete alias for :class:`array`.
80 Array objects support the ordinary sequence operations of indexing, slicing,
81 concatenation, and multiplication. When using slice assignment, the assigned
82 value must be an array object with the same type code; in all other cases,
83 :exc:`TypeError` is raised. Array objects also implement the buffer interface,
84 and may be used wherever buffer objects are supported.
86 The following data items and methods are also supported:
88 .. attribute:: array.typecode
90 The typecode character used to create the array.
93 .. attribute:: array.itemsize
95 The length in bytes of one array item in the internal representation.
98 .. method:: array.append(x)
100 Append a new item with value *x* to the end of the array.
103 .. method:: array.buffer_info()
105 Return a tuple ``(address, length)`` giving the current memory address and the
106 length in elements of the buffer used to hold array's contents. The size of the
107 memory buffer in bytes can be computed as ``array.buffer_info()[1] *
108 array.itemsize``. This is occasionally useful when working with low-level (and
109 inherently unsafe) I/O interfaces that require memory addresses, such as certain
110 :cfunc:`ioctl` operations. The returned numbers are valid as long as the array
111 exists and no length-changing operations are applied to it.
115 When using array objects from code written in C or C++ (the only way to
116 effectively make use of this information), it makes more sense to use the buffer
117 interface supported by array objects. This method is maintained for backward
118 compatibility and should be avoided in new code. The buffer interface is
119 documented in :ref:`bufferobjects`.
122 .. method:: array.byteswap()
124 "Byteswap" all items of the array. This is only supported for values which are
125 1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is
126 raised. It is useful when reading data from a file written on a machine with a
127 different byte order.
130 .. method:: array.count(x)
132 Return the number of occurrences of *x* in the array.
135 .. method:: array.extend(iterable)
137 Append items from *iterable* to the end of the array. If *iterable* is another
138 array, it must have *exactly* the same type code; if not, :exc:`TypeError` will
139 be raised. If *iterable* is not an array, it must be iterable and its elements
140 must be the right type to be appended to the array.
142 .. versionchanged:: 2.4
143 Formerly, the argument could only be another array.
146 .. method:: array.fromfile(f, n)
148 Read *n* items (as machine values) from the file object *f* and append them to
149 the end of the array. If less than *n* items are available, :exc:`EOFError` is
150 raised, but the items that were available are still inserted into the array.
151 *f* must be a real built-in file object; something else with a :meth:`read`
155 .. method:: array.fromlist(list)
157 Append items from the list. This is equivalent to ``for x in list:
158 a.append(x)`` except that if there is a type error, the array is unchanged.
161 .. method:: array.fromstring(s)
163 Appends items from the string, interpreting the string as an array of machine
164 values (as if it had been read from a file using the :meth:`fromfile` method).
167 .. method:: array.fromunicode(s)
169 Extends this array with data from the given unicode string. The array must
170 be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised. Use
171 ``array.fromstring(unicodestring.encode(enc))`` to append Unicode data to an
172 array of some other type.
175 .. method:: array.index(x)
177 Return the smallest *i* such that *i* is the index of the first occurrence of
181 .. method:: array.insert(i, x)
183 Insert a new item with value *x* in the array before position *i*. Negative
184 values are treated as being relative to the end of the array.
187 .. method:: array.pop([i])
189 Removes the item with the index *i* from the array and returns it. The optional
190 argument defaults to ``-1``, so that by default the last item is removed and
194 .. method:: array.read(f, n)
196 .. deprecated:: 1.5.1
197 Use the :meth:`fromfile` method.
199 Read *n* items (as machine values) from the file object *f* and append them to
200 the end of the array. If less than *n* items are available, :exc:`EOFError` is
201 raised, but the items that were available are still inserted into the array.
202 *f* must be a real built-in file object; something else with a :meth:`read`
206 .. method:: array.remove(x)
208 Remove the first occurrence of *x* from the array.
211 .. method:: array.reverse()
213 Reverse the order of the items in the array.
216 .. method:: array.tofile(f)
218 Write all items (as machine values) to the file object *f*.
221 .. method:: array.tolist()
223 Convert the array to an ordinary list with the same items.
226 .. method:: array.tostring()
228 Convert the array to an array of machine values and return the string
229 representation (the same sequence of bytes that would be written to a file by
230 the :meth:`tofile` method.)
233 .. method:: array.tounicode()
235 Convert the array to a unicode string. The array must be a type ``'u'`` array;
236 otherwise a :exc:`ValueError` is raised. Use ``array.tostring().decode(enc)`` to
237 obtain a unicode string from an array of some other type.
240 .. method:: array.write(f)
242 .. deprecated:: 1.5.1
243 Use the :meth:`tofile` method.
245 Write all items (as machine values) to the file object *f*.
247 When an array object is printed or converted to a string, it is represented as
248 ``array(typecode, initializer)``. The *initializer* is omitted if the array is
249 empty, otherwise it is a string if the *typecode* is ``'c'``, otherwise it is a
250 list of numbers. The string is guaranteed to be able to be converted back to an
251 array with the same type and value using :func:`eval`, so long as the
252 :func:`array` function has been imported using ``from array import array``.
256 array('c', 'hello world')
257 array('u', u'hello \u2641')
258 array('l', [1, 2, 3, 4, 5])
259 array('d', [1.0, 2.0, 3.14])
265 Packing and unpacking of heterogeneous binary data.
268 Packing and unpacking of External Data Representation (XDR) data as used in some
269 remote procedure call systems.
271 `The Numerical Python Manual <http://numpy.sourceforge.net/numdoc/HTML/numdoc.htm>`_
272 The Numeric Python extension (NumPy) defines another array type; see
273 http://numpy.sourceforge.net/ for further information about Numerical Python.
274 (A PDF version of the NumPy manual is available at
275 http://numpy.sourceforge.net/numdoc/numdoc.pdf).