Doc/library/array.rst - platform/external/python/cpython2 - Gitiles


 :mod:`array` --- Efficient arrays of numeric values
 ===================================================

 .. module:: array
    :synopsis: Space efficient arrays of uniformly typed numeric values.


 .. index:: single: arrays

 This module defines an object type which can compactly represent an array of
 basic values: characters, integers, floating point numbers.  Arrays are sequence
 types and behave very much like lists, except that the type of objects stored in
 them is constrained.  The type is specified at object creation time by using a
 :dfn:`type code`, which is a single character.  The following type codes are
 defined:

 +-----------+----------------+-------------------+-----------------------+
 | Type code | C Type         | Python Type       | Minimum size in bytes |
 +===========+================+===================+=======================+
 | ``'c'``   | char           | character         | 1                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'b'``   | signed char    | int               | 1                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'B'``   | unsigned char  | int               | 1                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'u'``   | Py_UNICODE     | Unicode character | 2 (see note)          |
 +-----------+----------------+-------------------+-----------------------+
 | ``'h'``   | signed short   | int               | 2                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'H'``   | unsigned short | int               | 2                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'i'``   | signed int     | int               | 2                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'I'``   | unsigned int   | long              | 2                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'l'``   | signed long    | int               | 4                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'L'``   | unsigned long  | long              | 4                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'f'``   | float          | float             | 4                     |
 +-----------+----------------+-------------------+-----------------------+
 | ``'d'``   | double         | float             | 8                     |
 +-----------+----------------+-------------------+-----------------------+

 .. note::

    The ``'u'`` typecode corresponds to Python's unicode character.  On narrow
    Unicode builds this is 2-bytes, on wide builds this is 4-bytes.

 The actual representation of values is determined by the machine architecture
 (strictly speaking, by the C implementation).  The actual size can be accessed
 through the :attr:`itemsize` attribute.  The values stored  for ``'L'`` and
 ``'I'`` items will be represented as Python long integers when retrieved,
 because Python's plain integer type cannot represent the full range of C's
 unsigned (long) integers.

 The module defines the following type:


 .. class:: array(typecode[, initializer])

    A new array whose items are restricted by *typecode*, and initialized
    from the optional *initializer* value, which must be a list, string, or iterable
    over elements of the appropriate type.

    .. versionchanged:: 2.4
       Formerly, only lists or strings were accepted.

    If given a list or string, the initializer is passed to the new array's
    :meth:`fromlist`, :meth:`fromstring`, or :meth:`fromunicode` method (see below)
    to add initial items to the array.  Otherwise, the iterable initializer is
    passed to the :meth:`extend` method.


 .. data:: ArrayType

    Obsolete alias for :class:`array`.

 Array objects support the ordinary sequence operations of indexing, slicing,
 concatenation, and multiplication.  When using slice assignment, the assigned
 value must be an array object with the same type code; in all other cases,
 :exc:`TypeError` is raised. Array objects also implement the buffer interface,
 and may be used wherever buffer objects are supported.

 The following data items and methods are also supported:

 .. attribute:: array.typecode

    The typecode character used to create the array.


 .. attribute:: array.itemsize

    The length in bytes of one array item in the internal representation.


 .. method:: array.append(x)

    Append a new item with value *x* to the end of the array.


 .. method:: array.buffer_info()

    Return a tuple ``(address, length)`` giving the current memory address and the
    length in elements of the buffer used to hold array's contents.  The size of the
    memory buffer in bytes can be computed as ``array.buffer_info()[1] *
    array.itemsize``.  This is occasionally useful when working with low-level (and
    inherently unsafe) I/O interfaces that require memory addresses, such as certain
    :cfunc:`ioctl` operations.  The returned numbers are valid as long as the array
    exists and no length-changing operations are applied to it.

    .. note::

       When using array objects from code written in C or C++ (the only way to
       effectively make use of this information), it makes more sense to use the buffer
       interface supported by array objects.  This method is maintained for backward
       compatibility and should be avoided in new code.  The buffer interface is
       documented in :ref:`bufferobjects`.


 .. method:: array.byteswap()

    "Byteswap" all items of the array.  This is only supported for values which are
    1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is
    raised.  It is useful when reading data from a file written on a machine with a
    different byte order.


 .. method:: array.count(x)

    Return the number of occurrences of *x* in the array.


 .. method:: array.extend(iterable)

    Append items from *iterable* to the end of the array.  If *iterable* is another
    array, it must have *exactly* the same type code; if not, :exc:`TypeError` will
    be raised.  If *iterable* is not an array, it must be iterable and its elements
    must be the right type to be appended to the array.

    .. versionchanged:: 2.4
       Formerly, the argument could only be another array.


 .. method:: array.fromfile(f, n)

    Read *n* items (as machine values) from the file object *f* and append them to
    the end of the array.  If less than *n* items are available, :exc:`EOFError` is
    raised, but the items that were available are still inserted into the array.
    *f* must be a real built-in file object; something else with a :meth:`read`
    method won't do.


 .. method:: array.fromlist(list)

    Append items from the list.  This is equivalent to ``for x in list:
    a.append(x)`` except that if there is a type error, the array is unchanged.


 .. method:: array.fromstring(s)

    Appends items from the string, interpreting the string as an array of machine
    values (as if it had been read from a file using the :meth:`fromfile` method).


 .. method:: array.fromunicode(s)

    Extends this array with data from the given unicode string.  The array must
    be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised.  Use
    ``array.fromstring(unicodestring.encode(enc))`` to append Unicode data to an
    array of some other type.


 .. method:: array.index(x)

    Return the smallest *i* such that *i* is the index of the first occurrence of
    *x* in the array.


 .. method:: array.insert(i, x)

    Insert a new item with value *x* in the array before position *i*. Negative
    values are treated as being relative to the end of the array.


 .. method:: array.pop([i])

    Removes the item with the index *i* from the array and returns it. The optional
    argument defaults to ``-1``, so that by default the last item is removed and
    returned.


 .. method:: array.read(f, n)

    .. deprecated:: 1.5.1
       Use the :meth:`fromfile` method.

    Read *n* items (as machine values) from the file object *f* and append them to
    the end of the array.  If less than *n* items are available, :exc:`EOFError` is
    raised, but the items that were available are still inserted into the array.
    *f* must be a real built-in file object; something else with a :meth:`read`
    method won't do.


 .. method:: array.remove(x)

    Remove the first occurrence of *x* from the array.


 .. method:: array.reverse()

    Reverse the order of the items in the array.


 .. method:: array.tofile(f)

    Write all items (as machine values) to the file object *f*.


 .. method:: array.tolist()

    Convert the array to an ordinary list with the same items.


 .. method:: array.tostring()

    Convert the array to an array of machine values and return the string
    representation (the same sequence of bytes that would be written to a file by
    the :meth:`tofile` method.)


 .. method:: array.tounicode()

    Convert the array to a unicode string.  The array must be a type ``'u'`` array;
    otherwise a :exc:`ValueError` is raised. Use ``array.tostring().decode(enc)`` to
    obtain a unicode string from an array of some other type.


 .. method:: array.write(f)

    .. deprecated:: 1.5.1
       Use the :meth:`tofile` method.

    Write all items (as machine values) to the file object *f*.

 When an array object is printed or converted to a string, it is represented as
 ``array(typecode, initializer)``.  The *initializer* is omitted if the array is
 empty, otherwise it is a string if the *typecode* is ``'c'``, otherwise it is a
 list of numbers.  The string is guaranteed to be able to be converted back to an
 array with the same type and value using :func:`eval`, so long as the
 :func:`array` function has been imported using ``from array import array``.
 Examples::

    array('l')
    array('c', 'hello world')
    array('u', u'hello \u2641')
    array('l', [1, 2, 3, 4, 5])
    array('d', [1.0, 2.0, 3.14])


 .. seealso::

    Module :mod:`struct`
       Packing and unpacking of heterogeneous binary data.

    Module :mod:`xdrlib`
       Packing and unpacking of External Data Representation (XDR) data as used in some
       remote procedure call systems.

    `The Numerical Python Manual <http://numpy.sourceforge.net/numdoc/HTML/numdoc.htm>`_
       The Numeric Python extension (NumPy) defines another array type; see
       http://numpy.sourceforge.net/ for further information about Numerical Python.
       (A PDF version of the NumPy manual is available at
       http://numpy.sourceforge.net/numdoc/numdoc.pdf).

	:mod:`array` --- Efficient arrays of numeric values
	===================================================

	.. module:: array
	:synopsis: Space efficient arrays of uniformly typed numeric values.


	.. index:: single: arrays

	This module defines an object type which can compactly represent an array of
	basic values: characters, integers, floating point numbers. Arrays are sequence
	types and behave very much like lists, except that the type of objects stored in
	them is constrained. The type is specified at object creation time by using a
	:dfn:`type code`, which is a single character. The following type codes are
	defined:

	+-----------+----------------+-------------------+-----------------------+
	\| Type code \| C Type \| Python Type \| Minimum size in bytes \|
	+===========+================+===================+=======================+
	\| ``'c'`` \| char \| character \| 1 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'b'`` \| signed char \| int \| 1 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'B'`` \| unsigned char \| int \| 1 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'u'`` \| Py_UNICODE \| Unicode character \| 2 (see note) \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'h'`` \| signed short \| int \| 2 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'H'`` \| unsigned short \| int \| 2 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'i'`` \| signed int \| int \| 2 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'I'`` \| unsigned int \| long \| 2 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'l'`` \| signed long \| int \| 4 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'L'`` \| unsigned long \| long \| 4 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'f'`` \| float \| float \| 4 \|
	+-----------+----------------+-------------------+-----------------------+
	\| ``'d'`` \| double \| float \| 8 \|
	+-----------+----------------+-------------------+-----------------------+

	.. note::

	The ``'u'`` typecode corresponds to Python's unicode character. On narrow
	Unicode builds this is 2-bytes, on wide builds this is 4-bytes.

	The actual representation of values is determined by the machine architecture
	(strictly speaking, by the C implementation). The actual size can be accessed
	through the :attr:`itemsize` attribute. The values stored for ``'L'`` and
	``'I'`` items will be represented as Python long integers when retrieved,
	because Python's plain integer type cannot represent the full range of C's
	unsigned (long) integers.

	The module defines the following type:


	.. class:: array(typecode[, initializer])

	A new array whose items are restricted by typecode, and initialized
	from the optional initializer value, which must be a list, string, or iterable
	over elements of the appropriate type.

	.. versionchanged:: 2.4
	Formerly, only lists or strings were accepted.

	If given a list or string, the initializer is passed to the new array's
	:meth:`fromlist`, :meth:`fromstring`, or :meth:`fromunicode` method (see below)
	to add initial items to the array. Otherwise, the iterable initializer is
	passed to the :meth:`extend` method.


	.. data:: ArrayType

	Obsolete alias for :class:`array`.

	Array objects support the ordinary sequence operations of indexing, slicing,
	concatenation, and multiplication. When using slice assignment, the assigned
	value must be an array object with the same type code; in all other cases,
	:exc:`TypeError` is raised. Array objects also implement the buffer interface,
	and may be used wherever buffer objects are supported.

	The following data items and methods are also supported:

	.. attribute:: array.typecode

	The typecode character used to create the array.


	.. attribute:: array.itemsize

	The length in bytes of one array item in the internal representation.


	.. method:: array.append(x)

	Append a new item with value x to the end of the array.


	.. method:: array.buffer_info()

	Return a tuple ``(address, length)`` giving the current memory address and the
	length in elements of the buffer used to hold array's contents. The size of the
	memory buffer in bytes can be computed as ``array.buffer_info()[1] *
	array.itemsize``. This is occasionally useful when working with low-level (and
	inherently unsafe) I/O interfaces that require memory addresses, such as certain
	:cfunc:`ioctl` operations. The returned numbers are valid as long as the array
	exists and no length-changing operations are applied to it.

	.. note::

	When using array objects from code written in C or C++ (the only way to
	effectively make use of this information), it makes more sense to use the buffer
	interface supported by array objects. This method is maintained for backward
	compatibility and should be avoided in new code. The buffer interface is
	documented in :ref:`bufferobjects`.


	.. method:: array.byteswap()

	"Byteswap" all items of the array. This is only supported for values which are
	1, 2, 4, or 8 bytes in size; for other types of values, :exc:`RuntimeError` is
	raised. It is useful when reading data from a file written on a machine with a
	different byte order.


	.. method:: array.count(x)

	Return the number of occurrences of x in the array.


	.. method:: array.extend(iterable)

	Append items from iterable to the end of the array. If iterable is another
	array, it must have exactly the same type code; if not, :exc:`TypeError` will
	be raised. If iterable is not an array, it must be iterable and its elements
	must be the right type to be appended to the array.

	.. versionchanged:: 2.4
	Formerly, the argument could only be another array.


	.. method:: array.fromfile(f, n)

	Read n items (as machine values) from the file object f and append them to
	the end of the array. If less than n items are available, :exc:`EOFError` is
	raised, but the items that were available are still inserted into the array.
	f must be a real built-in file object; something else with a :meth:`read`
	method won't do.


	.. method:: array.fromlist(list)

	Append items from the list. This is equivalent to ``for x in list:
	a.append(x)`` except that if there is a type error, the array is unchanged.


	.. method:: array.fromstring(s)

	Appends items from the string, interpreting the string as an array of machine
	values (as if it had been read from a file using the :meth:`fromfile` method).


	.. method:: array.fromunicode(s)

	Extends this array with data from the given unicode string. The array must
	be a type ``'u'`` array; otherwise a :exc:`ValueError` is raised. Use
	``array.fromstring(unicodestring.encode(enc))`` to append Unicode data to an
	array of some other type.


	.. method:: array.index(x)

	Return the smallest i such that i is the index of the first occurrence of
	x in the array.


	.. method:: array.insert(i, x)

	Insert a new item with value x in the array before position i. Negative
	values are treated as being relative to the end of the array.


	.. method:: array.pop([i])

	Removes the item with the index i from the array and returns it. The optional
	argument defaults to ``-1``, so that by default the last item is removed and
	returned.


	.. method:: array.read(f, n)

	.. deprecated:: 1.5.1
	Use the :meth:`fromfile` method.

	Read n items (as machine values) from the file object f and append them to
	the end of the array. If less than n items are available, :exc:`EOFError` is
	raised, but the items that were available are still inserted into the array.
	f must be a real built-in file object; something else with a :meth:`read`
	method won't do.


	.. method:: array.remove(x)

	Remove the first occurrence of x from the array.


	.. method:: array.reverse()

	Reverse the order of the items in the array.


	.. method:: array.tofile(f)

	Write all items (as machine values) to the file object f.


	.. method:: array.tolist()

	Convert the array to an ordinary list with the same items.


	.. method:: array.tostring()

	Convert the array to an array of machine values and return the string
	representation (the same sequence of bytes that would be written to a file by
	the :meth:`tofile` method.)


	.. method:: array.tounicode()

	Convert the array to a unicode string. The array must be a type ``'u'`` array;
	otherwise a :exc:`ValueError` is raised. Use ``array.tostring().decode(enc)`` to
	obtain a unicode string from an array of some other type.


	.. method:: array.write(f)

	.. deprecated:: 1.5.1
	Use the :meth:`tofile` method.

	Write all items (as machine values) to the file object f.

	When an array object is printed or converted to a string, it is represented as
	``array(typecode, initializer)``. The initializer is omitted if the array is
	empty, otherwise it is a string if the typecode is ``'c'``, otherwise it is a
	list of numbers. The string is guaranteed to be able to be converted back to an
	array with the same type and value using :func:`eval`, so long as the
	:func:`array` function has been imported using ``from array import array``.
	Examples::

	array('l')
	array('c', 'hello world')
	array('u', u'hello \u2641')
	array('l', [1, 2, 3, 4, 5])
	array('d', [1.0, 2.0, 3.14])


	.. seealso::

	Module :mod:`struct`
	Packing and unpacking of heterogeneous binary data.

	Module :mod:`xdrlib`
	Packing and unpacking of External Data Representation (XDR) data as used in some
	remote procedure call systems.

	`The Numerical Python Manual <http://numpy.sourceforge.net/numdoc/HTML/numdoc.htm>`_
	The Numeric Python extension (NumPy) defines another array type; see
	http://numpy.sourceforge.net/ for further information about Numerical Python.
	(A PDF version of the NumPy manual is available at
	http://numpy.sourceforge.net/numdoc/numdoc.pdf).