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17 | <title>5.18 fileinput -- Iterate over lines from multiple input streams</title> | |
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55 | <H1><A NAME="SECTION0071800000000000000000"> | |
56 | 5.18 <tt class="module">fileinput</tt> -- | |
57 | Iterate over lines from multiple input streams</A> | |
58 | </H1> | |
59 | <A NAME="module-fileinput"></A> | |
60 | ||
61 | <P> | |
62 | ||
63 | <P> | |
64 | This module implements a helper class and functions to quickly write a | |
65 | loop over standard input or a list of files. | |
66 | ||
67 | <P> | |
68 | The typical use is: | |
69 | ||
70 | <P> | |
71 | <div class="verbatim"><pre> | |
72 | import fileinput | |
73 | for line in fileinput.input(): | |
74 | process(line) | |
75 | </pre></div> | |
76 | ||
77 | <P> | |
78 | This iterates over the lines of all files listed in | |
79 | <code>sys.argv[1:]</code>, defaulting to <code>sys.stdin</code> if the list is | |
80 | empty. If a filename is <code>'-'</code>, it is also replaced by | |
81 | <code>sys.stdin</code>. To specify an alternative list of filenames, pass | |
82 | it as the first argument to <tt class="function">input()</tt>. A single file name is | |
83 | also allowed. | |
84 | ||
85 | <P> | |
86 | All files are opened in text mode. If an I/O error occurs during | |
87 | opening or reading a file, <tt class="exception">IOError</tt> is raised. | |
88 | ||
89 | <P> | |
90 | If <code>sys.stdin</code> is used more than once, the second and further use | |
91 | will return no lines, except perhaps for interactive use, or if it has | |
92 | been explicitly reset (e.g. using <code>sys.stdin.seek(0)</code>). | |
93 | ||
94 | <P> | |
95 | Empty files are opened and immediately closed; the only time their | |
96 | presence in the list of filenames is noticeable at all is when the | |
97 | last file opened is empty. | |
98 | ||
99 | <P> | |
100 | It is possible that the last line of a file does not end in a newline | |
101 | character; lines are returned including the trailing newline when it | |
102 | is present. | |
103 | ||
104 | <P> | |
105 | The following function is the primary interface of this module: | |
106 | ||
107 | <P> | |
108 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
109 | <td><nobr><b><tt id='l2h-1436' xml:id='l2h-1436' class="function">input</tt></b>(</nobr></td> | |
110 | <td><var></var><big>[</big><var>files</var><big>[</big><var>, | |
111 | inplace</var><big>[</big><var>, backup</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
112 | <dd> | |
113 | Create an instance of the <tt class="class">FileInput</tt> class. The instance | |
114 | will be used as global state for the functions of this module, and | |
115 | is also returned to use during iteration. The parameters to this | |
116 | function will be passed along to the constructor of the | |
117 | <tt class="class">FileInput</tt> class. | |
118 | </dl> | |
119 | ||
120 | <P> | |
121 | The following functions use the global state created by | |
122 | <tt class="function">input()</tt>; if there is no active state, | |
123 | <tt class="exception">RuntimeError</tt> is raised. | |
124 | ||
125 | <P> | |
126 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
127 | <td><nobr><b><tt id='l2h-1437' xml:id='l2h-1437' class="function">filename</tt></b>(</nobr></td> | |
128 | <td><var></var>)</td></tr></table></dt> | |
129 | <dd> | |
130 | Return the name of the file currently being read. Before the first | |
131 | line has been read, returns <code>None</code>. | |
132 | </dl> | |
133 | ||
134 | <P> | |
135 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
136 | <td><nobr><b><tt id='l2h-1438' xml:id='l2h-1438' class="function">lineno</tt></b>(</nobr></td> | |
137 | <td><var></var>)</td></tr></table></dt> | |
138 | <dd> | |
139 | Return the cumulative line number of the line that has just been | |
140 | read. Before the first line has been read, returns <code>0</code>. After | |
141 | the last line of the last file has been read, returns the line | |
142 | number of that line. | |
143 | </dl> | |
144 | ||
145 | <P> | |
146 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
147 | <td><nobr><b><tt id='l2h-1439' xml:id='l2h-1439' class="function">filelineno</tt></b>(</nobr></td> | |
148 | <td><var></var>)</td></tr></table></dt> | |
149 | <dd> | |
150 | Return the line number in the current file. Before the first line | |
151 | has been read, returns <code>0</code>. After the last line of the last | |
152 | file has been read, returns the line number of that line within the | |
153 | file. | |
154 | </dl> | |
155 | ||
156 | <P> | |
157 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
158 | <td><nobr><b><tt id='l2h-1440' xml:id='l2h-1440' class="function">isfirstline</tt></b>(</nobr></td> | |
159 | <td><var></var>)</td></tr></table></dt> | |
160 | <dd> | |
161 | Returns true if the line just read is the first line of its file, | |
162 | otherwise returns false. | |
163 | </dl> | |
164 | ||
165 | <P> | |
166 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
167 | <td><nobr><b><tt id='l2h-1441' xml:id='l2h-1441' class="function">isstdin</tt></b>(</nobr></td> | |
168 | <td><var></var>)</td></tr></table></dt> | |
169 | <dd> | |
170 | Returns true if the last line was read from <code>sys.stdin</code>, | |
171 | otherwise returns false. | |
172 | </dl> | |
173 | ||
174 | <P> | |
175 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
176 | <td><nobr><b><tt id='l2h-1442' xml:id='l2h-1442' class="function">nextfile</tt></b>(</nobr></td> | |
177 | <td><var></var>)</td></tr></table></dt> | |
178 | <dd> | |
179 | Close the current file so that the next iteration will read the | |
180 | first line from the next file (if any); lines not read from the file | |
181 | will not count towards the cumulative line count. The filename is | |
182 | not changed until after the first line of the next file has been | |
183 | read. Before the first line has been read, this function has no | |
184 | effect; it cannot be used to skip the first file. After the last | |
185 | line of the last file has been read, this function has no effect. | |
186 | </dl> | |
187 | ||
188 | <P> | |
189 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
190 | <td><nobr><b><tt id='l2h-1443' xml:id='l2h-1443' class="function">close</tt></b>(</nobr></td> | |
191 | <td><var></var>)</td></tr></table></dt> | |
192 | <dd> | |
193 | Close the sequence. | |
194 | </dl> | |
195 | ||
196 | <P> | |
197 | The class which implements the sequence behavior provided by the | |
198 | module is available for subclassing as well: | |
199 | ||
200 | <P> | |
201 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
202 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-1444' xml:id='l2h-1444' class="class">FileInput</tt></b>(</nobr></td> | |
203 | <td><var></var><big>[</big><var>files</var><big>[</big><var>, | |
204 | inplace</var><big>[</big><var>, backup</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
205 | <dd> | |
206 | Class <tt class="class">FileInput</tt> is the implementation; its methods | |
207 | <tt class="method">filename()</tt>, <tt class="method">lineno()</tt>, <tt class="method">fileline()</tt>, | |
208 | <tt class="method">isfirstline()</tt>, <tt class="method">isstdin()</tt>, <tt class="method">nextfile()</tt> and | |
209 | <tt class="method">close()</tt> correspond to the functions of the same name in the | |
210 | module. In addition it has a <tt class="method">readline()</tt> method which | |
211 | returns the next input line, and a <tt class="method">__getitem__()</tt> method | |
212 | which implements the sequence behavior. The sequence must be | |
213 | accessed in strictly sequential order; random access and | |
214 | <tt class="method">readline()</tt> cannot be mixed. | |
215 | </dl> | |
216 | ||
217 | <P> | |
218 | <strong>Optional in-place filtering:</strong> if the keyword argument | |
219 | <code><var>inplace</var>=1</code> is passed to <tt class="function">input()</tt> or to the | |
220 | <tt class="class">FileInput</tt> constructor, the file is moved to a backup file and | |
221 | standard output is directed to the input file (if a file of the same | |
222 | name as the backup file already exists, it will be replaced silently). | |
223 | This makes it possible to write a filter that rewrites its input file | |
224 | in place. If the keyword argument <code><var>backup</var>='.<some | |
225 | extension>'</code> is also given, it specifies the extension for the backup | |
226 | file, and the backup file remains around; by default, the extension is | |
227 | <code>'.bak'</code> and it is deleted when the output file is closed. In-place | |
228 | filtering is disabled when standard input is read. | |
229 | ||
230 | <P> | |
231 | <strong>Caveat:</strong> The current implementation does not work for MS-DOS | |
232 | 8+3 filesystems. | |
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