Doc/library/array.rst - platform/external/python/cpython3 - 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 | Notes |
 +===========+====================+===================+=======================+=======+
 | ``'b'``   | signed char        | int               | 1                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'B'``   | unsigned char      | int               | 1                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'u'``   | Py_UNICODE         | Unicode character | 2                     | \(1)  |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'h'``   | signed short       | int               | 2                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'H'``   | unsigned short     | int               | 2                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'i'``   | signed int         | int               | 2                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'I'``   | unsigned int       | int               | 2                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'l'``   | signed long        | int               | 4                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'L'``   | unsigned long      | int               | 4                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'q'``   | signed long long   | int               | 8                     | \(2)  |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'Q'``   | unsigned long long | int               | 8                     | \(2)  |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'f'``   | float              | float             | 4                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+
 | ``'d'``   | double             | float             | 8                     |       |
 +-----------+--------------------+-------------------+-----------------------+-------+

 Notes:

 (1)
    The ``'u'`` type code corresponds to Python's obsolete unicode character
    (:c:type:`Py_UNICODE` which is :c:type:`wchar_t`). Depending on the
    platform, it can be 16 bits or 32 bits.

    ``'u'`` will be removed together with the rest of the :c:type:`Py_UNICODE`
    API.

    .. deprecated-removed:: 3.3 4.0

 (2)
    The ``'q'`` and ``'Q'`` type codes are available only if
    the platform C compiler used to build Python supports C :c:type:`long long`,
    or, on Windows, :c:type:`__int64`.

    .. versionadded:: 3.3

 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 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, object
    supporting the buffer interface, or iterable over elements of the
    appropriate type.

    If given a list or string, the initializer is passed to the new array's
    :meth:`fromlist`, :meth:`frombytes`, 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:: typecodes

    A string with all available type codes.

 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
    :c:func:`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.


 .. method:: array.frombytes(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).

    .. versionadded:: 3.2
       :meth:`fromstring` is renamed to :meth:`frombytes` for clarity.


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

    Read *n* items (as machine values) from the :term:`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()

    Deprecated alias for :meth:`frombytes`.


 .. 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.frombytes(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.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.tobytes()

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

    .. versionadded:: 3.2
       :meth:`tostring` is renamed to :meth:`tobytes` for clarity.


 .. method:: array.tofile(f)

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


 .. method:: array.tolist()

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


 .. method:: array.tostring()

    Deprecated alias for :meth:`tobytes`.


 .. 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.tobytes().decode(enc)`` to
    obtain a unicode string from an array of some other type.


 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 ``'u'``, 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('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 \| Notes \|
	+===========+====================+===================+=======================+=======+
	\| ``'b'`` \| signed char \| int \| 1 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'B'`` \| unsigned char \| int \| 1 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'u'`` \| Py_UNICODE \| Unicode character \| 2 \| \(1) \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'h'`` \| signed short \| int \| 2 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'H'`` \| unsigned short \| int \| 2 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'i'`` \| signed int \| int \| 2 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'I'`` \| unsigned int \| int \| 2 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'l'`` \| signed long \| int \| 4 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'L'`` \| unsigned long \| int \| 4 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'q'`` \| signed long long \| int \| 8 \| \(2) \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'Q'`` \| unsigned long long \| int \| 8 \| \(2) \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'f'`` \| float \| float \| 4 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+
	\| ``'d'`` \| double \| float \| 8 \| \|
	+-----------+--------------------+-------------------+-----------------------+-------+

	Notes:

	(1)
	The ``'u'`` type code corresponds to Python's obsolete unicode character
	(:c:type:`Py_UNICODE` which is :c:type:`wchar_t`). Depending on the
	platform, it can be 16 bits or 32 bits.

	``'u'`` will be removed together with the rest of the :c:type:`Py_UNICODE`
	API.

	.. deprecated-removed:: 3.3 4.0

	(2)
	The ``'q'`` and ``'Q'`` type codes are available only if
	the platform C compiler used to build Python supports C :c:type:`long long`,
	or, on Windows, :c:type:`__int64`.

	.. versionadded:: 3.3

	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 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, object
	supporting the buffer interface, or iterable over elements of the
	appropriate type.

	If given a list or string, the initializer is passed to the new array's
	:meth:`fromlist`, :meth:`frombytes`, 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:: typecodes

	A string with all available type codes.

	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
	:c:func:`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.


	.. method:: array.frombytes(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).

	.. versionadded:: 3.2
	:meth:`fromstring` is renamed to :meth:`frombytes` for clarity.


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

	Read n items (as machine values) from the :term:`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()

	Deprecated alias for :meth:`frombytes`.


	.. 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.frombytes(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.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.tobytes()

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

	.. versionadded:: 3.2
	:meth:`tostring` is renamed to :meth:`tobytes` for clarity.


	.. method:: array.tofile(f)

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


	.. method:: array.tolist()

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


	.. method:: array.tostring()

	Deprecated alias for :meth:`tobytes`.


	.. 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.tobytes().decode(enc)`` to
	obtain a unicode string from an array of some other type.


	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 ``'u'``, 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('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).