1 2:mod:`array` --- Efficient arrays of numeric values 3=================================================== 4 5.. module:: array 6 :synopsis: Space efficient arrays of uniformly typed numeric values. 7 8 9.. index:: single: arrays 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 | 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+-----------+----------------+-------------------+-----------------------+ 45 46.. note:: 47 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. 50 51The actual representation of values is determined by the machine architecture 52(strictly speaking, by the C implementation). The actual size can be accessed 53through the :attr:`itemsize` attribute. The values stored for ``'L'`` and 54``'I'`` items will be represented as Python long integers when retrieved, 55because Python's plain integer type cannot represent the full range of C's 56unsigned (long) integers. 57 58The module defines the following type: 59 60 61.. class:: array(typecode[, initializer]) 62 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. 66 67 .. versionchanged:: 2.4 68 Formerly, only lists or strings were accepted. 69 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. 74 75 76.. data:: ArrayType 77 78 Obsolete alias for :class:`~array.array`. 79 80Array objects support the ordinary sequence operations of indexing, slicing, 81concatenation, and multiplication. When using slice assignment, the assigned 82value 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, 84and may be used wherever buffer objects are supported. 85 86The following data items and methods are also supported: 87 88.. attribute:: array.typecode 89 90 The typecode character used to create the array. 91 92 93.. attribute:: array.itemsize 94 95 The length in bytes of one array item in the internal representation. 96 97 98.. method:: array.append(x) 99 100 Append a new item with value *x* to the end of the array. 101 102 103.. method:: array.buffer_info() 104 105 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 :c:func:`ioctl` operations. The returned numbers are valid as long as the array 111 exists and no length-changing operations are applied to it. 112 113 .. note:: 114 115 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`. 120 121 122.. method:: array.byteswap() 123 124 "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. 128 129 130.. method:: array.count(x) 131 132 Return the number of occurrences of *x* in the array. 133 134 135.. method:: array.extend(iterable) 136 137 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. 141 142 .. versionchanged:: 2.4 143 Formerly, the argument could only be another array. 144 145 146.. method:: array.fromfile(f, n) 147 148 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` 152 method won't do. 153 154 155.. method:: array.fromlist(list) 156 157 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. 159 160 161.. method:: array.fromstring(s) 162 163 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). 165 166 167.. method:: array.fromunicode(s) 168 169 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. 173 174 175.. method:: array.index(x) 176 177 Return the smallest *i* such that *i* is the index of the first occurrence of 178 *x* in the array. 179 180 181.. method:: array.insert(i, x) 182 183 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. 185 186 187.. method:: array.pop([i]) 188 189 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 191 returned. 192 193 194.. method:: array.read(f, n) 195 196 .. deprecated:: 1.5.1 197 Use the :meth:`fromfile` method. 198 199 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` 203 method won't do. 204 205 206.. method:: array.remove(x) 207 208 Remove the first occurrence of *x* from the array. 209 210 211.. method:: array.reverse() 212 213 Reverse the order of the items in the array. 214 215 216.. method:: array.tofile(f) 217 218 Write all items (as machine values) to the file object *f*. 219 220 221.. method:: array.tolist() 222 223 Convert the array to an ordinary list with the same items. 224 225 226.. method:: array.tostring() 227 228 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.) 231 232 233.. method:: array.tounicode() 234 235 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. 238 239 240.. method:: array.write(f) 241 242 .. deprecated:: 1.5.1 243 Use the :meth:`tofile` method. 244 245 Write all items (as machine values) to the file object *f*. 246 247When 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 249empty, otherwise it is a string if the *typecode* is ``'c'``, otherwise it is a 250list of numbers. The string is guaranteed to be able to be converted back to an 251array with the same type and value using :func:`eval`, so long as the 252:class:`~array.array` class has been imported using ``from array import array``. 253Examples:: 254 255 array('l') 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]) 260 261 262.. seealso:: 263 264 Module :mod:`struct` 265 Packing and unpacking of heterogeneous binary data. 266 267 Module :mod:`xdrlib` 268 Packing and unpacking of External Data Representation (XDR) data as used in some 269 remote procedure call systems. 270 271 `The Numerical Python Documentation <https://docs.scipy.org/doc/>`_ 272 The Numeric Python extension (NumPy) defines another array type; see 273 http://www.numpy.org/ for further information about Numerical Python. 274 275