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authorcinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
committercinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
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+\section{\module{array} ---
+ Efficient arrays of numeric values}
+
+\declaremodule{builtin}{array}
+\modulesynopsis{Efficient arrays of uniformly typed numeric values.}
+
+
+This module defines an object type which can efficiently represent
+an array of basic values: characters, integers, floating point
+numbers. Arrays\index{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:
+
+\begin{tableiv}{c|l|l|c}{code}{Type code}{C Type}{Python Type}{Minimum size in bytes}
+ \lineiv{'c'}{char} {character} {1}
+ \lineiv{'b'}{signed char} {int} {1}
+ \lineiv{'B'}{unsigned char} {int} {1}
+ \lineiv{'u'}{Py_UNICODE} {Unicode character}{2}
+ \lineiv{'h'}{signed short} {int} {2}
+ \lineiv{'H'}{unsigned short}{int} {2}
+ \lineiv{'i'}{signed int} {int} {2}
+ \lineiv{'I'}{unsigned int} {long} {2}
+ \lineiv{'l'}{signed long} {int} {4}
+ \lineiv{'L'}{unsigned long} {long} {4}
+ \lineiv{'f'}{float} {float} {4}
+ \lineiv{'d'}{double} {float} {8}
+\end{tableiv}
+
+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 \member{itemsize} attribute. The values
+stored for \code{'L'} and \code{'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:
+
+\begin{funcdesc}{array}{typecode\optional{, initializer}}
+Return a new array whose items are restricted by \var{typecode},
+and initialized from the optional \var{initializer} value, which
+must be a list, string, or iterable over elements of the
+appropriate type.
+\versionchanged[Formerly, only lists or strings were accepted]{2.4}
+If given a list or string, the initializer is passed to the
+new array's \method{fromlist()}, \method{fromstring()}, or
+\method{fromunicode()} method (see below) to add initial items to
+the array. Otherwise, the iterable initializer is passed to the
+\method{extend()} method.
+\end{funcdesc}
+
+\begin{datadesc}{ArrayType}
+Obsolete alias for \function{array}.
+\end{datadesc}
+
+
+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, \exception{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:
+
+\begin{memberdesc}[array]{typecode}
+The typecode character used to create the array.
+\end{memberdesc}
+
+\begin{memberdesc}[array]{itemsize}
+The length in bytes of one array item in the internal representation.
+\end{memberdesc}
+
+
+\begin{methoddesc}[array]{append}{x}
+Append a new item with value \var{x} to the end of the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{buffer_info}{}
+Return a tuple \code{(\var{address}, \var{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 \code{\var{array}.buffer_info()[1] *
+\var{array}.itemsize}. This is occasionally useful when working with
+low-level (and inherently unsafe) I/O interfaces that require memory
+addresses, such as certain \cfunction{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
+\Cpp{} (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
+the \citetitle[../api/newTypes.html]{Python/C API Reference Manual}.}
+\end{methoddesc}
+
+\begin{methoddesc}[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, \exception{RuntimeError} is raised. It is useful when reading
+data from a file written on a machine with a different byte order.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{count}{x}
+Return the number of occurrences of \var{x} in the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{extend}{iterable}
+Append items from \var{iterable} to the end of the array. If
+\var{iterable} is another array, it must have \emph{exactly} the same
+type code; if not, \exception{TypeError} will be raised. If
+\var{iterable} is not an array, it must be iterable and its
+elements must be the right type to be appended to the array.
+\versionchanged[Formerly, the argument could only be another array]{2.4}
+\end{methoddesc}
+
+\begin{methoddesc}[array]{fromfile}{f, n}
+Read \var{n} items (as machine values) from the file object \var{f}
+and append them to the end of the array. If less than \var{n} items
+are available, \exception{EOFError} is raised, but the items that were
+available are still inserted into the array. \var{f} must be a real
+built-in file object; something else with a \method{read()} method won't
+do.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{fromlist}{list}
+Append items from the list. This is equivalent to
+\samp{for x in \var{list}:\ a.append(x)}
+except that if there is a type error, the array is unchanged.
+\end{methoddesc}
+
+\begin{methoddesc}[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 \method{fromfile()} method).
+\end{methoddesc}
+
+\begin{methoddesc}[array]{fromunicode}{s}
+Extends this array with data from the given unicode string. The array
+must be a type \code{'u'} array; otherwise a \exception{ValueError}
+is raised. Use \samp{array.fromstring(ustr.decode(enc))} to
+append Unicode data to an array of some other type.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{index}{x}
+Return the smallest \var{i} such that \var{i} is the index of
+the first occurrence of \var{x} in the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{insert}{i, x}
+Insert a new item with value \var{x} in the array before position
+\var{i}. Negative values are treated as being relative to the end
+of the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{pop}{\optional{i}}
+Removes the item with the index \var{i} from the array and returns
+it. The optional argument defaults to \code{-1}, so that by default
+the last item is removed and returned.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{read}{f, n}
+\deprecated {1.5.1}
+ {Use the \method{fromfile()} method.}
+Read \var{n} items (as machine values) from the file object \var{f}
+and append them to the end of the array. If less than \var{n} items
+are available, \exception{EOFError} is raised, but the items that were
+available are still inserted into the array. \var{f} must be a real
+built-in file object; something else with a \method{read()} method won't
+do.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{remove}{x}
+Remove the first occurrence of \var{x} from the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{reverse}{}
+Reverse the order of the items in the array.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{tofile}{f}
+Write all items (as machine values) to the file object \var{f}.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{tolist}{}
+Convert the array to an ordinary list with the same items.
+\end{methoddesc}
+
+\begin{methoddesc}[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 \method{tofile()} method.)
+\end{methoddesc}
+
+\begin{methoddesc}[array]{tounicode}{}
+Convert the array to a unicode string. The array must be
+a type \code{'u'} array; otherwise a \exception{ValueError} is raised.
+Use \samp{array.tostring().decode(enc)} to obtain a unicode string
+from an array of some other type.
+\end{methoddesc}
+
+\begin{methoddesc}[array]{write}{f}
+\deprecated {1.5.1}
+ {Use the \method{tofile()} method.}
+Write all items (as machine values) to the file object \var{f}.
+\end{methoddesc}
+
+When an array object is printed or converted to a string, it is
+represented as \code{array(\var{typecode}, \var{initializer})}. The
+\var{initializer} is omitted if the array is empty, otherwise it is a
+string if the \var{typecode} is \code{'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 reverse quotes
+(\code{``}), so long as the \function{array()} function has been
+imported using \code{from array import array}. Examples:
+
+\begin{verbatim}
+array('l')
+array('c', 'hello world')
+array('u', u'hello \textbackslash u2641')
+array('l', [1, 2, 3, 4, 5])
+array('d', [1.0, 2.0, 3.14])
+\end{verbatim}
+
+
+\begin{seealso}
+ \seemodule{struct}{Packing and unpacking of heterogeneous binary data.}
+ \seemodule{xdrlib}{Packing and unpacking of External Data
+ Representation (XDR) data as used in some remote
+ procedure call systems.}
+ \seetitle[http://numpy.sourceforge.net/numdoc/HTML/numdoc.htm]{The
+ Numerical Python Manual}{The Numeric Python extension
+ (NumPy) defines another array type; see
+ \url{http://numpy.sourceforge.net/} for further information
+ about Numerical Python. (A PDF version of the NumPy manual
+ is available at
+ \url{http://numpy.sourceforge.net/numdoc/numdoc.pdf}).}
+\end{seealso}