\section{\module{array} ---

Efficient arrays of numeric values}

\declaremodule{builtin}{array}

\modulesynopsis{Efficient arrays of uniformly typed numeric values.}

This module defines a new 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{tableiii}{c|l|c}{code}{Type code}{C Type}{Minimum size in bytes}

\lineiii{'c'}{character}{1}

\lineiii{'b'}{signed int}{1}

\lineiii{'B'}{unsigned int}{1}

\lineiii{'h'}{signed int}{2}

\lineiii{'H'}{unsigned int}{2}

\lineiii{'i'}{signed int}{2}

\lineiii{'I'}{unsigned int}{2}

\lineiii{'l'}{signed int}{4}

\lineiii{'L'}{unsigned int}{4}

\lineiii{'f'}{float}{4}

\lineiii{'d'}{double}{8}

\end{tableiii}

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 function and type object:

\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 or a string. The list or string is passed to the new array's

\method{fromlist()} or \method{fromstring()} method (see below) to add

initial items to the array.

\end{funcdesc}

\begin{datadesc}{ArrayType}

Type object corresponding to the objects returned by

\function{array()}.

\end{datadesc}

Array objects support the following data items and methods:

\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 bytes of the buffer used to hold

array's contents. 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.

\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 occurences of \var{x} in the array.

\end{methoddesc}

\begin{methoddesc}[array]{extend}{a}

Append array items from \var{a} to the end of the array.

\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 (i.e. as if it had been read from a

file using the \method{fromfile()} method).

\end{methoddesc}

\begin{methoddesc}[array]{index}{x}

Return the smallest \var{i} such that \var{i} is the index of

the first occurence 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}.

\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 occurence 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]{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