1 :mod:`fileinput` --- Iterate over lines from multiple input streams 2 =================================================================== 3 4 .. module:: fileinput 5 :synopsis: Loop over standard input or a list of files. 6 .. moduleauthor:: Guido van Rossum <guido (a] python.org> 7 .. sectionauthor:: Fred L. Drake, Jr. <fdrake (a] acm.org> 8 9 **Source code:** :source:`Lib/fileinput.py` 10 11 -------------- 12 13 This module implements a helper class and functions to quickly write a 14 loop over standard input or a list of files. If you just want to read or 15 write one file see :func:`open`. 16 17 The typical use is:: 18 19 import fileinput 20 for line in fileinput.input(): 21 process(line) 22 23 This iterates over the lines of all files listed in ``sys.argv[1:]``, defaulting 24 to ``sys.stdin`` if the list is empty. If a filename is ``'-'``, it is also 25 replaced by ``sys.stdin``. To specify an alternative list of filenames, pass it 26 as the first argument to :func:`.input`. A single file name is also allowed. 27 28 All files are opened in text mode by default, but you can override this by 29 specifying the *mode* parameter in the call to :func:`.input` or 30 :class:`FileInput()`. If an I/O error occurs during opening or reading a file, 31 :exc:`IOError` is raised. 32 33 If ``sys.stdin`` is used more than once, the second and further use will return 34 no lines, except perhaps for interactive use, or if it has been explicitly reset 35 (e.g. using ``sys.stdin.seek(0)``). 36 37 Empty files are opened and immediately closed; the only time their presence in 38 the list of filenames is noticeable at all is when the last file opened is 39 empty. 40 41 Lines are returned with any newlines intact, which means that the last line in 42 a file may not have one. 43 44 You can control how files are opened by providing an opening hook via the 45 *openhook* parameter to :func:`fileinput.input` or :class:`FileInput()`. The 46 hook must be a function that takes two arguments, *filename* and *mode*, and 47 returns an accordingly opened file-like object. Two useful hooks are already 48 provided by this module. 49 50 The following function is the primary interface of this module: 51 52 53 .. function:: input([files[, inplace[, backup[, bufsize[, mode[, openhook]]]]]]) 54 55 Create an instance of the :class:`FileInput` class. The instance will be used 56 as global state for the functions of this module, and is also returned to use 57 during iteration. The parameters to this function will be passed along to the 58 constructor of the :class:`FileInput` class. 59 60 .. versionchanged:: 2.5 61 Added the *mode* and *openhook* parameters. 62 63 .. versionchanged:: 2.7.12 64 The *bufsize* parameter is no longer used. 65 66 The following functions use the global state created by :func:`fileinput.input`; 67 if there is no active state, :exc:`RuntimeError` is raised. 68 69 70 .. function:: filename() 71 72 Return the name of the file currently being read. Before the first line has 73 been read, returns ``None``. 74 75 76 .. function:: fileno() 77 78 Return the integer "file descriptor" for the current file. When no file is 79 opened (before the first line and between files), returns ``-1``. 80 81 .. versionadded:: 2.5 82 83 84 .. function:: lineno() 85 86 Return the cumulative line number of the line that has just been read. Before 87 the first line has been read, returns ``0``. After the last line of the last 88 file has been read, returns the line number of that line. 89 90 91 .. function:: filelineno() 92 93 Return the line number in the current file. Before the first line has been 94 read, returns ``0``. After the last line of the last file has been read, 95 returns the line number of that line within the file. 96 97 98 .. function:: isfirstline() 99 100 Returns true if the line just read is the first line of its file, otherwise 101 returns false. 102 103 104 .. function:: isstdin() 105 106 Returns true if the last line was read from ``sys.stdin``, otherwise returns 107 false. 108 109 110 .. function:: nextfile() 111 112 Close the current file so that the next iteration will read the first line from 113 the next file (if any); lines not read from the file will not count towards the 114 cumulative line count. The filename is not changed until after the first line 115 of the next file has been read. Before the first line has been read, this 116 function has no effect; it cannot be used to skip the first file. After the 117 last line of the last file has been read, this function has no effect. 118 119 120 .. function:: close() 121 122 Close the sequence. 123 124 The class which implements the sequence behavior provided by the module is 125 available for subclassing as well: 126 127 128 .. class:: FileInput([files[, inplace[, backup[,bufsize[, mode[, openhook]]]]]]) 129 130 Class :class:`FileInput` is the implementation; its methods :meth:`filename`, 131 :meth:`fileno`, :meth:`lineno`, :meth:`filelineno`, :meth:`isfirstline`, 132 :meth:`isstdin`, :meth:`nextfile` and :meth:`close` correspond to the 133 functions of the same name in the module. In addition it has a 134 :meth:`~file.readline` method which returns the next input line, 135 and a :meth:`__getitem__` method which implements the sequence behavior. 136 The sequence must be accessed in strictly sequential order; random access 137 and :meth:`~file.readline` cannot be mixed. 138 139 With *mode* you can specify which file mode will be passed to :func:`open`. It 140 must be one of ``'r'``, ``'rU'``, ``'U'`` and ``'rb'``. 141 142 The *openhook*, when given, must be a function that takes two arguments, 143 *filename* and *mode*, and returns an accordingly opened file-like object. You 144 cannot use *inplace* and *openhook* together. 145 146 .. versionchanged:: 2.5 147 Added the *mode* and *openhook* parameters. 148 149 .. versionchanged:: 2.7.12 150 The *bufsize* parameter is no longer used. 151 152 **Optional in-place filtering:** if the keyword argument ``inplace=1`` is passed 153 to :func:`fileinput.input` or to the :class:`FileInput` constructor, the file is 154 moved to a backup file and standard output is directed to the input file (if a 155 file of the same name as the backup file already exists, it will be replaced 156 silently). This makes it possible to write a filter that rewrites its input 157 file in place. If the *backup* parameter is given (typically as 158 ``backup='.<some extension>'``), it specifies the extension for the backup file, 159 and the backup file remains around; by default, the extension is ``'.bak'`` and 160 it is deleted when the output file is closed. In-place filtering is disabled 161 when standard input is read. 162 163 .. note:: 164 165 The current implementation does not work for MS-DOS 8+3 filesystems. 166 167 168 The two following opening hooks are provided by this module: 169 170 .. function:: hook_compressed(filename, mode) 171 172 Transparently opens files compressed with gzip and bzip2 (recognized by the 173 extensions ``'.gz'`` and ``'.bz2'``) using the :mod:`gzip` and :mod:`bz2` 174 modules. If the filename extension is not ``'.gz'`` or ``'.bz2'``, the file is 175 opened normally (ie, using :func:`open` without any decompression). 176 177 Usage example: ``fi = fileinput.FileInput(openhook=fileinput.hook_compressed)`` 178 179 .. versionadded:: 2.5 180 181 182 .. function:: hook_encoded(encoding) 183 184 Returns a hook which opens each file with :func:`io.open`, using the given 185 *encoding* to read the file. 186 187 Usage example: ``fi = 188 fileinput.FileInput(openhook=fileinput.hook_encoded("iso-8859-1"))`` 189 190 .. note:: 191 192 With this hook, :class:`FileInput` might return Unicode strings depending on the 193 specified *encoding*. 194 195 .. versionadded:: 2.5 196 197
