Next: math Prev: __main__ Up: Built-in Modules Top: Top

3.4. Built-in module array

This module defines a new object type which can efficiently 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 type code, which is a single character. The following type codes are defined:

Typecode
Type --- Minimal size in bytes

'c'
character --- 1
'b'
signed integer --- 1
'h'
signed integer --- 2
'i'
signed integer --- 2
'l'
signed integer --- 4
'f'
floating point --- 4
'd'
floating point --- 8
The actual representation of values is determined by the machine architecture (strictly spoken, by the C implementation). The actual size can be accessed through the typecode attribute.

The module defines the following function:

array (typecode, initializer) -- function of module array
Return a new array whose items are restricted by typecode, and initialized from the optional initializer value, which must be a list or a string. The list or string is passed to the new array's fromlist() or fromstring() method (see below) to add initial items to the array.
Array objects support the following data items and methods:

typecode -- data of module array
The typecode character used to create the array.
itemsize -- data of module array
The length in bytes of one array item in the internal representation.
append (x) -- function of module array
Append a new item with value x to the end of the array.
byteswap (x) -- function of module array
``Byteswap'' all items of the array. This is only supported for integer values. It is useful when reading data ffrom a file written on a machine with a different byte order.
fromfile (f, n) -- function of module array
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, EOFError is raised, but the items that were available are still inserted into the array.
fromlist (list) -- function of module array
Appends 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.
fromstring (s) -- function of module array
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 fromfile() method).
insert (i, x) -- function of module array
Insert a new item with value x in the array before position i.
tofile (f) -- function of module array
Write all items (as machine values) to the file object f.
tolist () -- function of module array
Convert the array to an ordinary list with the same items.
tostring () -- function of module array
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 tofile() method.)
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 reverse quotes (``). Examples: