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 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 16 defined: 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'`` | Py_UNICODE | 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 | \(2) | 40 +-----------+--------------------+-------------------+-----------------------+-------+ 41 | ``'Q'`` | unsigned long long | int | 8 | \(2) | 42 +-----------+--------------------+-------------------+-----------------------+-------+ 43 | ``'f'`` | float | float | 4 | | 44 +-----------+--------------------+-------------------+-----------------------+-------+ 45 | ``'d'`` | double | float | 8 | | 46 +-----------+--------------------+-------------------+-----------------------+-------+ 47 48 Notes: 49 50 (1) 51 The ``'u'`` type code corresponds to Python's obsolete unicode character 52 (:c:type:`Py_UNICODE` which is :c:type:`wchar_t`). Depending on the 53 platform, it can be 16 bits or 32 bits. 54 55 ``'u'`` will be removed together with the rest of the :c:type:`Py_UNICODE` 56 API. 57 58 .. deprecated-removed:: 3.3 4.0 59 60 (2) 61 The ``'q'`` and ``'Q'`` type codes are available only if 62 the platform C compiler used to build Python supports C :c:type:`long long`, 63 or, on Windows, :c:type:`__int64`. 64 65 .. versionadded:: 3.3 66 67 The actual representation of values is determined by the machine architecture 68 (strictly speaking, by the C implementation). The actual size can be accessed 69 through the :attr:`itemsize` attribute. 70 71 The module defines the following type: 72 73 74 .. class:: array(typecode[, initializer]) 75 76 A new array whose items are restricted by *typecode*, and initialized 77 from the optional *initializer* value, which must be a list, a 78 :term:`bytes-like object`, or iterable over elements of the 79 appropriate type. 80 81 If given a list or string, the initializer is passed to the new array's 82 :meth:`fromlist`, :meth:`frombytes`, or :meth:`fromunicode` method (see below) 83 to add initial items to the array. Otherwise, the iterable initializer is 84 passed to the :meth:`extend` method. 85 86 87 .. data:: typecodes 88 89 A string with all available type codes. 90 91 Array objects support the ordinary sequence operations of indexing, slicing, 92 concatenation, and multiplication. When using slice assignment, the assigned 93 value must be an array object with the same type code; in all other cases, 94 :exc:`TypeError` is raised. Array objects also implement the buffer interface, 95 and may be used wherever :term:`bytes-like objects <bytes-like object>` are supported. 96 97 The following data items and methods are also supported: 98 99 .. attribute:: array.typecode 100 101 The typecode character used to create the array. 102 103 104 .. attribute:: array.itemsize 105 106 The length in bytes of one array item in the internal representation. 107 108 109 .. method:: array.append(x) 110 111 Append a new item with value *x* to the end of the array. 112 113 114 .. method:: array.buffer_info() 115 116 Return a tuple ``(address, length)`` giving the current memory address and the 117 length in elements of the buffer used to hold array's contents. The size of the 118 memory buffer in bytes can be computed as ``array.buffer_info()[1] * 119 array.itemsize``. This is occasionally useful when working with low-level (and 120 inherently unsafe) I/O interfaces that require memory addresses, such as certain 121 :c:func:`ioctl` operations. The returned numbers are valid as long as the array 122 exists and no length-changing operations are applied to it. 123 124 .. note:: 125 126 When using array objects from code written in C or C++ (the only way to 127 effectively make use of this information), it makes more sense to use the buffer 128 interface supported by array objects. This method is maintained for backward 129 compatibility and should be avoided in new code. The buffer interface is 130 documented in :ref:`bufferobjects`. 131 132 133 .. method:: array.byteswap() 134 135 "Byteswap" all items of the array. This is only supported for values which are 136 1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is 137 raised. It is useful when reading data from a file written on a machine with a 138 different byte order. 139 140 141 .. method:: array.count(x) 142 143 Return the number of occurrences of *x* in the array. 144 145 146 .. method:: array.extend(iterable) 147 148 Append items from *iterable* to the end of the array. If *iterable* is another 149 array, it must have *exactly* the same type code; if not, :exc:`TypeError` will 150 be raised. If *iterable* is not an array, it must be iterable and its elements 151 must be the right type to be appended to the array. 152 153 154 .. method:: array.frombytes(s) 155 156 Appends items from the string, interpreting the string as an array of machine 157 values (as if it had been read from a file using the :meth:`fromfile` method). 158 159 .. versionadded:: 3.2 160 :meth:`fromstring` is renamed to :meth:`frombytes` for clarity. 161 162 163 .. method:: array.fromfile(f, n) 164 165 Read *n* items (as machine values) from the :term:`file object` *f* and append 166 them to the end of the array. If less than *n* items are available, 167 :exc:`EOFError` is raised, but the items that were available are still 168 inserted into the array. *f* must be a real built-in file object; something 169 else with a :meth:`read` method won't do. 170 171 172 .. method:: array.fromlist(list) 173 174 Append items from the list. This is equivalent to ``for x in list: 175 a.append(x)`` except that if there is a type error, the array is unchanged. 176 177 178 .. method:: array.fromstring() 179 180 Deprecated alias for :meth:`frombytes`. 181 182 183 .. method:: array.fromunicode(s) 184 185 Extends this array with data from the given unicode string. The array must 186 be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised. Use 187 ``array.frombytes(unicodestring.encode(enc))`` to append Unicode data to an 188 array of some other type. 189 190 191 .. method:: array.index(x) 192 193 Return the smallest *i* such that *i* is the index of the first occurrence of 194 *x* in the array. 195 196 197 .. method:: array.insert(i, x) 198 199 Insert a new item with value *x* in the array before position *i*. Negative 200 values are treated as being relative to the end of the array. 201 202 203 .. method:: array.pop([i]) 204 205 Removes the item with the index *i* from the array and returns it. The optional 206 argument defaults to ``-1``, so that by default the last item is removed and 207 returned. 208 209 210 .. method:: array.remove(x) 211 212 Remove the first occurrence of *x* from the array. 213 214 215 .. method:: array.reverse() 216 217 Reverse the order of the items in the array. 218 219 220 .. method:: array.tobytes() 221 222 Convert the array to an array of machine values and return the bytes 223 representation (the same sequence of bytes that would be written to a file by 224 the :meth:`tofile` method.) 225 226 .. versionadded:: 3.2 227 :meth:`tostring` is renamed to :meth:`tobytes` for clarity. 228 229 230 .. method:: array.tofile(f) 231 232 Write all items (as machine values) to the :term:`file object` *f*. 233 234 235 .. method:: array.tolist() 236 237 Convert the array to an ordinary list with the same items. 238 239 240 .. method:: array.tostring() 241 242 Deprecated alias for :meth:`tobytes`. 243 244 245 .. method:: array.tounicode() 246 247 Convert the array to a unicode string. The array must be a type ``'u'`` array; 248 otherwise a :exc:`ValueError` is raised. Use ``array.tobytes().decode(enc)`` to 249 obtain a unicode string from an array of some other type. 250 251 252 When an array object is printed or converted to a string, it is represented as 253 ``array(typecode, initializer)``. The *initializer* is omitted if the array is 254 empty, otherwise it is a string if the *typecode* is ``'u'``, otherwise it is a 255 list of numbers. The string is guaranteed to be able to be converted back to an 256 array with the same type and value using :func:`eval`, so long as the 257 :class:`~array.array` class has been imported using ``from array import array``. 258 Examples:: 259 260 array('l') 261 array('u', 'hello \u2641') 262 array('l', [1, 2, 3, 4, 5]) 263 array('d', [1.0, 2.0, 3.14]) 264 265 266 .. seealso:: 267 268 Module :mod:`struct` 269 Packing and unpacking of heterogeneous binary data. 270 271 Module :mod:`xdrlib` 272 Packing and unpacking of External Data Representation (XDR) data as used in some 273 remote procedure call systems. 274 275 `The Numerical Python Documentation <https://docs.scipy.org/doc/>`_ 276 The Numeric Python extension (NumPy) defines another array type; see 277 http://www.numpy.org/ for further information about Numerical Python. 278 279
