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