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Added buffer_info() docs.
author Guido van Rossum <guido@python.org>
date Thu, 14 Aug 1997 19:50:37 +0000
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1 \section{Built-in Module \sectcode{array}}
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2 \label{module-array}
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3 \bimodindex{array}
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4 \index{arrays}
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5
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6 This module defines a new object type which can efficiently represent
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7 an array of basic values: characters, integers, floating point
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8 numbers. Arrays are sequence types and behave very much like lists,
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9 except that the type of objects stored in them is constrained. The
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10 type is specified at object creation time by using a \dfn{type code},
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11 which is a single character. The following type codes are defined:
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12
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13 \begin{tableiii}{|c|c|c|}{code}{Typecode}{Type}{Minimal size in bytes}
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14 \lineiii{'c'}{character}{1}
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15 \lineiii{'b'}{signed integer}{1}
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16 \lineiii{'B'}{unsigned integer}{1}
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17 \lineiii{'h'}{signed integer}{2}
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18 \lineiii{'H'}{unsigned integer}{2}
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19 \lineiii{'i'}{signed integer}{2}
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20 \lineiii{'I'}{unsigned integer}{2}
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21 \lineiii{'l'}{signed integer}{4}
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22 \lineiii{'L'}{unsigned integer}{4}
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23 \lineiii{'f'}{floating point}{4}
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24 \lineiii{'d'}{floating point}{8}
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25 \end{tableiii}
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26
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27 The actual representation of values is determined by the machine
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28 architecture (strictly speaking, by the C implementation). The actual
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29 size can be accessed through the \var{itemsize} attribute. The values
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30 stored for \code{'L'} and \code{'I'} items will be represented as
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31 Python long integers when retrieved, because Python's plain integer
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32 type can't represent the full range of C's unsigned (long) integers.
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33
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34 See also built-in module \code{struct}.
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35 \bimodindex{struct}
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36
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37 The module defines the following function:
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38
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39 \renewcommand{\indexsubitem}{(in module array)}
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40
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41 \begin{funcdesc}{array}{typecode\optional{\, initializer}}
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42 Return a new array whose items are restricted by \var{typecode}, and
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43 initialized from the optional \var{initializer} value, which must be a
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44 list or a string. The list or string is passed to the new array's
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45 \code{fromlist()} or \code{fromstring()} method (see below) to add
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46 initial items to the array.
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47 \end{funcdesc}
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48
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49 Array objects support the following data items and methods:
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50
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51 \begin{datadesc}{typecode}
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52 The typecode character used to create the array.
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53 \end{datadesc}
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54
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55 \begin{datadesc}{itemsize}
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56 The length in bytes of one array item in the internal representation.
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57 \end{datadesc}
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58
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59 \begin{funcdesc}{append}{x}
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60 Append a new item with value \var{x} to the end of the array.
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61 \end{funcdesc}
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62
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63 \begin{funcdesc}{buffer_info}{}
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64 Return a tuple \code{(\var{address}, var{length})} giving the current
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65 memory address and the length in bytes of the buffer used to hold
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66 array's contents. This is occasionally useful when working with
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67 low-level (and inherently unsafe) I/O interfaces that require memory
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68 addresses, such as certain \code{ioctl} operations. The returned
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69 numbers are valid as long as the array exists and no length-changing
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70 operations are applied to it.
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71 \end{funcdesc}
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72
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73 \begin{funcdesc}{byteswap}{x}
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74 ``Byteswap'' all items of the array. This is only supported for
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75 integer values. It is useful when reading data from a file written
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76 on a machine with a different byte order.
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77 \end{funcdesc}
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78
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79 \begin{funcdesc}{fromfile}{f\, n}
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80 Read \var{n} items (as machine values) from the file object \var{f}
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81 and append them to the end of the array. If less than \var{n} items
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82 are available, \code{EOFError} is raised, but the items that were
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83 available are still inserted into the array. \var{f} must be a real
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84 built-in file object; something else with a \code{read()} method won't
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85 do.
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86 \end{funcdesc}
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87
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88 \begin{funcdesc}{fromlist}{list}
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89 Append items from the list. This is equivalent to
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90 \code{for x in \var{list}:\ a.append(x)}
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91 except that if there is a type error, the array is unchanged.
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92 \end{funcdesc}
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93
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94 \begin{funcdesc}{fromstring}{s}
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95 Appends items from the string, interpreting the string as an
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96 array of machine values (i.e. as if it had been read from a
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97 file using the \code{fromfile()} method).
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98 \end{funcdesc}
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99
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100 \begin{funcdesc}{insert}{i\, x}
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101 Insert a new item with value \var{x} in the array before position
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102 \var{i}.
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103 \end{funcdesc}
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104
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105 \begin{funcdesc}{tofile}{f}
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106 Write all items (as machine values) to the file object \var{f}.
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107 \end{funcdesc}
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108
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109 \begin{funcdesc}{tolist}{}
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110 Convert the array to an ordinary list with the same items.
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111 \end{funcdesc}
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112
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113 \begin{funcdesc}{tostring}{}
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114 Convert the array to an array of machine values and return the
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115 string representation (the same sequence of bytes that would
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116 be written to a file by the \code{tofile()} method.)
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117 \end{funcdesc}
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118
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119 When an array object is printed or converted to a string, it is
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120 represented as \code{array(\var{typecode}, \var{initializer})}. The
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121 \var{initializer} is omitted if the array is empty, otherwise it is a
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122 string if the \var{typecode} is \code{'c'}, otherwise it is a list of
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123 numbers. The string is guaranteed to be able to be converted back to
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124 an array with the same type and value using reverse quotes
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125 (\code{``}). Examples:
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126
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127 \bcode\begin{verbatim}
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128 array('l')
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129 array('c', 'hello world')
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130 array('l', [1, 2, 3, 4, 5])
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131 array('d', [1.0, 2.0, 3.14])
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132 \end{verbatim}\ecode