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mass changes; fix titles; add examples; correct typos; clarifications; unified style; etc.
author Guido van Rossum <guido@python.org>
date Fri, 17 Mar 1995 16:07:09 +0000
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1 \section{Built-in Module \sectcode{array}}
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2 \bimodindex{array}
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3 \index{arrays}
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4
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5 This module defines a new object type which can efficiently represent
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6 an array of basic values: characters, integers, floating point
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7 numbers. Arrays are sequence types and behave very much like lists,
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8 except that the type of objects stored in them is constrained. The
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9 type is specified at object creation time by using a \dfn{type code},
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10 which is a single character. The following type codes are defined:
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11
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12 \begin{tableiii}{|c|c|c|}{code}{Typecode}{Type}{Minimal size in bytes}
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13 \lineiii{'c'}{character}{1}
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14 \lineiii{'b'}{signed integer}{1}
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15 \lineiii{'h'}{signed integer}{2}
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16 \lineiii{'i'}{signed integer}{2}
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17 \lineiii{'l'}{signed integer}{4}
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18 \lineiii{'f'}{floating point}{4}
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19 \lineiii{'d'}{floating point}{8}
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20 \end{tableiii}
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21
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22 The actual representation of values is determined by the machine
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23 architecture (strictly speaking, by the C implementation). The actual
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24 size can be accessed through the \var{itemsize} attribute.
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25
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26 The module defines the following function:
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27
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28 \renewcommand{\indexsubitem}{(in module array)}
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29
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30 \begin{funcdesc}{array}{typecode\optional{\, initializer}}
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31 Return a new array whose items are restricted by \var{typecode}, and
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32 initialized from the optional \var{initializer} value, which must be a
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33 list or a string. The list or string is passed to the new array's
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34 \code{fromlist()} or \code{fromstring()} method (see below) to add
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35 initial items to the array.
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36 \end{funcdesc}
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37
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38 Array objects support the following data items and methods:
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39
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40 \begin{datadesc}{typecode}
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41 The typecode character used to create the array.
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42 \end{datadesc}
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43
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44 \begin{datadesc}{itemsize}
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45 The length in bytes of one array item in the internal representation.
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46 \end{datadesc}
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47
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48 \begin{funcdesc}{append}{x}
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49 Append a new item with value \var{x} to the end of the array.
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50 \end{funcdesc}
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51
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52 \begin{funcdesc}{byteswap}{x}
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53 ``Byteswap'' all items of the array. This is only supported for
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54 integer values. It is useful when reading data from a file written
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55 on a machine with a different byte order.
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56 \end{funcdesc}
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57
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58 \begin{funcdesc}{fromfile}{f\, n}
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59 Read \var{n} items (as machine values) from the file object \var{f}
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60 and append them to the end of the array. If less than \var{n} items
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61 are available, \code{EOFError} is raised, but the items that were
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62 available are still inserted into the array. \var{f} must be a real
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63 built-in file object; something else with a \code{read()} method won't
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64 do.
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65 \end{funcdesc}
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66
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67 \begin{funcdesc}{fromlist}{list}
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68 Append items from the list. This is equivalent to
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69 \code{for x in \var{list}:\ a.append(x)}
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70 except that if there is a type error, the array is unchanged.
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71 \end{funcdesc}
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72
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73 \begin{funcdesc}{fromstring}{s}
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74 Appends items from the string, interpreting the string as an
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75 array of machine values (i.e. as if it had been read from a
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76 file using the \code{fromfile()} method).
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77 \end{funcdesc}
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78
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79 \begin{funcdesc}{insert}{i\, x}
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80 Insert a new item with value \var{x} in the array before position
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81 \var{i}.
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82 \end{funcdesc}
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83
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84 \begin{funcdesc}{tofile}{f}
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85 Write all items (as machine values) to the file object \var{f}.
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86 \end{funcdesc}
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87
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88 \begin{funcdesc}{tolist}{}
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89 Convert the array to an ordinary list with the same items.
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90 \end{funcdesc}
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91
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92 \begin{funcdesc}{tostring}{}
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93 Convert the array to an array of machine values and return the
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94 string representation (the same sequence of bytes that would
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95 be written to a file by the \code{tofile()} method.)
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96 \end{funcdesc}
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97
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98 When an array object is printed or converted to a string, it is
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99 represented as \code{array(\var{typecode}, \var{initializer})}. The
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100 \var{initializer} is omitted if the array is empty, otherwise it is a
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101 string if the \var{typecode} is \code{'c'}, otherwise it is a list of
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102 numbers. The string is guaranteed to be able to be converted back to
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103 an array with the same type and value using reverse quotes
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104 (\code{``}). Examples:
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105
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106 \bcode\begin{verbatim}
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107 array('l')
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108 array('c', 'hello world')
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109 array('l', [1, 2, 3, 4, 5])
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110 array('d', [1.0, 2.0, 3.14])
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111 \end{verbatim}\ecode