1:mod:`array` --- Efficient arrays of numeric values
2===================================================
3
4.. module:: array
5   :synopsis: Space efficient arrays of uniformly typed numeric values.
6
7.. index:: single: arrays
8
9--------------
10
11This module defines an object type which can compactly represent an array of
12basic values: characters, integers, floating point numbers.  Arrays are sequence
13types and behave very much like lists, except that the type of objects stored in
14them 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
16defined:
17
18+-----------+--------------------+-------------------+-----------------------+-------+
19| Type code | C Type             | Python Type       | Minimum size in bytes | Notes |
20+===========+====================+===================+=======================+=======+
21| ``'b'``   | signed char        | int               | 1                     |       |
22+-----------+--------------------+-------------------+-----------------------+-------+
23| ``'B'``   | unsigned char      | int               | 1                     |       |
24+-----------+--------------------+-------------------+-----------------------+-------+
25| ``'u'``   | wchar_t            | Unicode character | 2                     | \(1)  |
26+-----------+--------------------+-------------------+-----------------------+-------+
27| ``'h'``   | signed short       | int               | 2                     |       |
28+-----------+--------------------+-------------------+-----------------------+-------+
29| ``'H'``   | unsigned short     | int               | 2                     |       |
30+-----------+--------------------+-------------------+-----------------------+-------+
31| ``'i'``   | signed int         | int               | 2                     |       |
32+-----------+--------------------+-------------------+-----------------------+-------+
33| ``'I'``   | unsigned int       | int               | 2                     |       |
34+-----------+--------------------+-------------------+-----------------------+-------+
35| ``'l'``   | signed long        | int               | 4                     |       |
36+-----------+--------------------+-------------------+-----------------------+-------+
37| ``'L'``   | unsigned long      | int               | 4                     |       |
38+-----------+--------------------+-------------------+-----------------------+-------+
39| ``'q'``   | signed long long   | int               | 8                     |       |
40+-----------+--------------------+-------------------+-----------------------+-------+
41| ``'Q'``   | unsigned long long | int               | 8                     |       |
42+-----------+--------------------+-------------------+-----------------------+-------+
43| ``'f'``   | float              | float             | 4                     |       |
44+-----------+--------------------+-------------------+-----------------------+-------+
45| ``'d'``   | double             | float             | 8                     |       |
46+-----------+--------------------+-------------------+-----------------------+-------+
47
48Notes:
49
50(1)
51   It can be 16 bits or 32 bits depending on the platform.
52
53   .. versionchanged:: 3.9
54      ``array('u')`` now uses ``wchar_t`` as C type instead of deprecated
55      ``Py_UNICODE``. This change doesn't affect to its behavior because
56      ``Py_UNICODE`` is alias of ``wchar_t`` since Python 3.3.
57
58   .. deprecated-removed:: 3.3 4.0
59
60
61The actual representation of values is determined by the machine architecture
62(strictly speaking, by the C implementation).  The actual size can be accessed
63through the :attr:`itemsize` attribute.
64
65The module defines the following type:
66
67
68.. class:: array(typecode[, initializer])
69
70   A new array whose items are restricted by *typecode*, and initialized
71   from the optional *initializer* value, which must be a list, a
72   :term:`bytes-like object`, or iterable over elements of the
73   appropriate type.
74
75   If given a list or string, the initializer is passed to the new array's
76   :meth:`fromlist`, :meth:`frombytes`, or :meth:`fromunicode` method (see below)
77   to add initial items to the array.  Otherwise, the iterable initializer is
78   passed to the :meth:`extend` method.
79
80   .. audit-event:: array.__new__ typecode,initializer array.array
81
82.. data:: typecodes
83
84   A string with all available type codes.
85
86Array objects support the ordinary sequence operations of indexing, slicing,
87concatenation, and multiplication.  When using slice assignment, the assigned
88value must be an array object with the same type code; in all other cases,
89:exc:`TypeError` is raised. Array objects also implement the buffer interface,
90and may be used wherever :term:`bytes-like objects <bytes-like object>` are supported.
91
92The following data items and methods are also supported:
93
94.. attribute:: array.typecode
95
96   The typecode character used to create the array.
97
98
99.. attribute:: array.itemsize
100
101   The length in bytes of one array item in the internal representation.
102
103
104.. method:: array.append(x)
105
106   Append a new item with value *x* to the end of the array.
107
108
109.. method:: array.buffer_info()
110
111   Return a tuple ``(address, length)`` giving the current memory address and the
112   length in elements of the buffer used to hold array's contents.  The size of the
113   memory buffer in bytes can be computed as ``array.buffer_info()[1] *
114   array.itemsize``.  This is occasionally useful when working with low-level (and
115   inherently unsafe) I/O interfaces that require memory addresses, such as certain
116   :c:func:`ioctl` operations.  The returned numbers are valid as long as the array
117   exists and no length-changing operations are applied to it.
118
119   .. note::
120
121      When using array objects from code written in C or C++ (the only way to
122      effectively make use of this information), it makes more sense to use the buffer
123      interface supported by array objects.  This method is maintained for backward
124      compatibility and should be avoided in new code.  The buffer interface is
125      documented in :ref:`bufferobjects`.
126
127
128.. method:: array.byteswap()
129
130   "Byteswap" all items of the array.  This is only supported for values which are
131   1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is
132   raised.  It is useful when reading data from a file written on a machine with a
133   different byte order.
134
135
136.. method:: array.count(x)
137
138   Return the number of occurrences of *x* in the array.
139
140
141.. method:: array.extend(iterable)
142
143   Append items from *iterable* to the end of the array.  If *iterable* is another
144   array, it must have *exactly* the same type code; if not, :exc:`TypeError` will
145   be raised.  If *iterable* is not an array, it must be iterable and its elements
146   must be the right type to be appended to the array.
147
148
149.. method:: array.frombytes(s)
150
151   Appends items from the string, interpreting the string as an array of machine
152   values (as if it had been read from a file using the :meth:`fromfile` method).
153
154   .. versionadded:: 3.2
155      :meth:`fromstring` is renamed to :meth:`frombytes` for clarity.
156
157
158.. method:: array.fromfile(f, n)
159
160   Read *n* items (as machine values) from the :term:`file object` *f* and append
161   them to the end of the array.  If less than *n* items are available,
162   :exc:`EOFError` is raised, but the items that were available are still
163   inserted into the array. *f* must be a real built-in file object; something
164   else with a :meth:`read` method won't do.
165
166
167.. method:: array.fromlist(list)
168
169   Append items from the list.  This is equivalent to ``for x in list:
170   a.append(x)`` except that if there is a type error, the array is unchanged.
171
172
173.. method:: array.fromunicode(s)
174
175   Extends this array with data from the given unicode string.  The array must
176   be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised.  Use
177   ``array.frombytes(unicodestring.encode(enc))`` to append Unicode data to an
178   array of some other type.
179
180
181.. method:: array.index(x)
182
183   Return the smallest *i* such that *i* is the index of the first occurrence of
184   *x* in the array.
185
186
187.. method:: array.insert(i, x)
188
189   Insert a new item with value *x* in the array before position *i*. Negative
190   values are treated as being relative to the end of the array.
191
192
193.. method:: array.pop([i])
194
195   Removes the item with the index *i* from the array and returns it. The optional
196   argument defaults to ``-1``, so that by default the last item is removed and
197   returned.
198
199
200.. method:: array.remove(x)
201
202   Remove the first occurrence of *x* from the array.
203
204
205.. method:: array.reverse()
206
207   Reverse the order of the items in the array.
208
209
210.. method:: array.tobytes()
211
212   Convert the array to an array of machine values and return the bytes
213   representation (the same sequence of bytes that would be written to a file by
214   the :meth:`tofile` method.)
215
216   .. versionadded:: 3.2
217      :meth:`tostring` is renamed to :meth:`tobytes` for clarity.
218
219
220.. method:: array.tofile(f)
221
222   Write all items (as machine values) to the :term:`file object` *f*.
223
224
225.. method:: array.tolist()
226
227   Convert the array to an ordinary list with the same items.
228
229
230.. method:: array.tounicode()
231
232   Convert the array to a unicode string.  The array must be a type ``'u'`` array;
233   otherwise a :exc:`ValueError` is raised. Use ``array.tobytes().decode(enc)`` to
234   obtain a unicode string from an array of some other type.
235
236
237When an array object is printed or converted to a string, it is represented as
238``array(typecode, initializer)``.  The *initializer* is omitted if the array is
239empty, otherwise it is a string if the *typecode* is ``'u'``, otherwise it is a
240list of numbers.  The string is guaranteed to be able to be converted back to an
241array with the same type and value using :func:`eval`, so long as the
242:class:`~array.array` class has been imported using ``from array import array``.
243Examples::
244
245   array('l')
246   array('u', 'hello \u2641')
247   array('l', [1, 2, 3, 4, 5])
248   array('d', [1.0, 2.0, 3.14])
249
250
251.. seealso::
252
253   Module :mod:`struct`
254      Packing and unpacking of heterogeneous binary data.
255
256   Module :mod:`xdrlib`
257      Packing and unpacking of External Data Representation (XDR) data as used in some
258      remote procedure call systems.
259
260   `The Numerical Python Documentation <https://docs.scipy.org/doc/>`_
261      The Numeric Python extension (NumPy) defines another array type; see
262      http://www.numpy.org/ for further information about Numerical Python.
263
264