Commit | Line | Data |
---|---|---|
920dae64 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
2 | <html> | |
3 | <head> | |
4 | <link rel="STYLESHEET" href="lib.css" type='text/css' /> | |
5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
7 | <link rel="first" href="lib.html" title='Python Library Reference' /> | |
8 | <link rel='contents' href='contents.html' title="Contents" /> | |
9 | <link rel='index' href='genindex.html' title='Index' /> | |
10 | <link rel='last' href='about.html' title='About this document...' /> | |
11 | <link rel='help' href='about.html' title='About this document...' /> | |
12 | <link rel="next" href="module-colorsys.html" /> | |
13 | <link rel="prev" href="module-wave.html" /> | |
14 | <link rel="parent" href="mmedia.html" /> | |
15 | <link rel="next" href="module-colorsys.html" /> | |
16 | <meta name='aesop' content='information' /> | |
17 | <title>14.6 chunk -- Read IFF chunked data</title> | |
18 | </head> | |
19 | <body> | |
20 | <DIV CLASS="navigation"> | |
21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
23 | <tr> | |
24 | <td class='online-navigation'><a rel="prev" title="14.5.2 Wave_write Objects" | |
25 | href="Wave-write-objects.html"><img src='../icons/previous.png' | |
26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
27 | <td class='online-navigation'><a rel="parent" title="14. Multimedia Services" | |
28 | href="mmedia.html"><img src='../icons/up.png' | |
29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
30 | <td class='online-navigation'><a rel="next" title="14.7 colorsys " | |
31 | href="module-colorsys.html"><img src='../icons/next.png' | |
32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
33 | <td align="center" width="100%">Python Library Reference</td> | |
34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
35 | href="contents.html"><img src='../icons/contents.png' | |
36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
37 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
38 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
39 | <td class='online-navigation'><a rel="index" title="Index" | |
40 | href="genindex.html"><img src='../icons/index.png' | |
41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
42 | </tr></table> | |
43 | <div class='online-navigation'> | |
44 | <b class="navlabel">Previous:</b> | |
45 | <a class="sectref" rel="prev" href="Wave-write-objects.html">14.5.2 Wave_write Objects</A> | |
46 | <b class="navlabel">Up:</b> | |
47 | <a class="sectref" rel="parent" href="mmedia.html">14. Multimedia Services</A> | |
48 | <b class="navlabel">Next:</b> | |
49 | <a class="sectref" rel="next" href="module-colorsys.html">14.7 colorsys </A> | |
50 | </div> | |
51 | <hr /></div> | |
52 | </DIV> | |
53 | <!--End of Navigation Panel--> | |
54 | ||
55 | <H1><A NAME="SECTION0016600000000000000000"> | |
56 | 14.6 <tt class="module">chunk</tt> -- | |
57 | Read IFF chunked data</A> | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | <A NAME="module-chunk"></A> | |
62 | ||
63 | <P> | |
64 | This module provides an interface for reading files that use EA IFF 85 | |
65 | chunks.<A NAME="tex2html164" | |
66 | HREF="#foot67687"><SUP>14.1</SUP></A> This format is used | |
67 | in at least the Audio<a id='l2h-4745' xml:id='l2h-4745'></a> Interchange File Format | |
68 | (AIFF/AIFF-C) and the Real<a id='l2h-4746' xml:id='l2h-4746'></a> Media File | |
69 | Format<a id='l2h-4747' xml:id='l2h-4747'></a> (RMFF). The WAVE audio file format is closely | |
70 | related and can also be read using this module. | |
71 | ||
72 | <P> | |
73 | A chunk has the following structure: | |
74 | ||
75 | <P> | |
76 | <div class="center"><table class="realtable"> | |
77 | <thead> | |
78 | <tr> | |
79 | <th class="center">Offset</th> | |
80 | <th class="center">Length</th> | |
81 | <th class="left" >Contents</th> | |
82 | </tr> | |
83 | </thead> | |
84 | <tbody> | |
85 | <tr><td class="center" valign="baseline">0</td> | |
86 | <td class="center">4</td> | |
87 | <td class="left" >Chunk ID</td></tr> | |
88 | <tr><td class="center" valign="baseline">4</td> | |
89 | <td class="center">4</td> | |
90 | <td class="left" >Size of chunk in big-endian byte order, not including the | |
91 | header</td></tr> | |
92 | <tr><td class="center" valign="baseline">8</td> | |
93 | <td class="center"><var>n</var></td> | |
94 | <td class="left" >Data bytes, where <var>n</var> is the size given in | |
95 | the preceding field</td></tr> | |
96 | <tr><td class="center" valign="baseline">8 + <var>n</var></td> | |
97 | <td class="center">0 or 1</td> | |
98 | <td class="left" >Pad byte needed if <var>n</var> is odd and | |
99 | chunk alignment is used</td></tr></tbody> | |
100 | </table></div> | |
101 | ||
102 | <P> | |
103 | The ID is a 4-byte string which identifies the type of chunk. | |
104 | ||
105 | <P> | |
106 | The size field (a 32-bit value, encoded using big-endian byte order) | |
107 | gives the size of the chunk data, not including the 8-byte header. | |
108 | ||
109 | <P> | |
110 | Usually an IFF-type file consists of one or more chunks. The proposed | |
111 | usage of the <tt class="class">Chunk</tt> class defined here is to instantiate an | |
112 | instance at the start of each chunk and read from the instance until | |
113 | it reaches the end, after which a new instance can be instantiated. | |
114 | At the end of the file, creating a new instance will fail with a | |
115 | <tt class="exception">EOFError</tt> exception. | |
116 | ||
117 | <P> | |
118 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
119 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-4736' xml:id='l2h-4736' class="class">Chunk</tt></b>(</nobr></td> | |
120 | <td><var>file</var><big>[</big><var>, align, bigendian, inclheader</var><big>]</big><var></var>)</td></tr></table></dt> | |
121 | <dd> | |
122 | Class which represents a chunk. The <var>file</var> argument is expected | |
123 | to be a file-like object. An instance of this class is specifically | |
124 | allowed. The only method that is needed is <tt class="method">read()</tt>. If the | |
125 | methods <tt class="method">seek()</tt> and <tt class="method">tell()</tt> are present and don't | |
126 | raise an exception, they are also used. If these methods are present | |
127 | and raise an exception, they are expected to not have altered the | |
128 | object. If the optional argument <var>align</var> is true, chunks are | |
129 | assumed to be aligned on 2-byte boundaries. If <var>align</var> is | |
130 | false, no alignment is assumed. The default value is true. If the | |
131 | optional argument <var>bigendian</var> is false, the chunk size is assumed | |
132 | to be in little-endian order. This is needed for WAVE audio files. | |
133 | The default value is true. If the optional argument <var>inclheader</var> | |
134 | is true, the size given in the chunk header includes the size of the | |
135 | header. The default value is false. | |
136 | </dl> | |
137 | ||
138 | <P> | |
139 | A <tt class="class">Chunk</tt> object supports the following methods: | |
140 | ||
141 | <P> | |
142 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
143 | <td><nobr><b><tt id='l2h-4737' xml:id='l2h-4737' class="method">getname</tt></b>(</nobr></td> | |
144 | <td><var></var>)</td></tr></table></dt> | |
145 | <dd> | |
146 | Returns the name (ID) of the chunk. This is the first 4 bytes of the | |
147 | chunk. | |
148 | </dl> | |
149 | ||
150 | <P> | |
151 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
152 | <td><nobr><b><tt id='l2h-4738' xml:id='l2h-4738' class="method">getsize</tt></b>(</nobr></td> | |
153 | <td><var></var>)</td></tr></table></dt> | |
154 | <dd> | |
155 | Returns the size of the chunk. | |
156 | </dl> | |
157 | ||
158 | <P> | |
159 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
160 | <td><nobr><b><tt id='l2h-4739' xml:id='l2h-4739' class="method">close</tt></b>(</nobr></td> | |
161 | <td><var></var>)</td></tr></table></dt> | |
162 | <dd> | |
163 | Close and skip to the end of the chunk. This does not close the | |
164 | underlying file. | |
165 | </dl> | |
166 | ||
167 | <P> | |
168 | The remaining methods will raise <tt class="exception">IOError</tt> if called after | |
169 | the <tt class="method">close()</tt> method has been called. | |
170 | ||
171 | <P> | |
172 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
173 | <td><nobr><b><tt id='l2h-4740' xml:id='l2h-4740' class="method">isatty</tt></b>(</nobr></td> | |
174 | <td><var></var>)</td></tr></table></dt> | |
175 | <dd> | |
176 | Returns <code>False</code>. | |
177 | </dl> | |
178 | ||
179 | <P> | |
180 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
181 | <td><nobr><b><tt id='l2h-4741' xml:id='l2h-4741' class="method">seek</tt></b>(</nobr></td> | |
182 | <td><var>pos</var><big>[</big><var>, whence</var><big>]</big><var></var>)</td></tr></table></dt> | |
183 | <dd> | |
184 | Set the chunk's current position. The <var>whence</var> argument is | |
185 | optional and defaults to <code>0</code> (absolute file positioning); other | |
186 | values are <code>1</code> (seek relative to the current position) and | |
187 | <code>2</code> (seek relative to the file's end). There is no return value. | |
188 | If the underlying file does not allow seek, only forward seeks are | |
189 | allowed. | |
190 | </dl> | |
191 | ||
192 | <P> | |
193 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
194 | <td><nobr><b><tt id='l2h-4742' xml:id='l2h-4742' class="method">tell</tt></b>(</nobr></td> | |
195 | <td><var></var>)</td></tr></table></dt> | |
196 | <dd> | |
197 | Return the current position into the chunk. | |
198 | </dl> | |
199 | ||
200 | <P> | |
201 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
202 | <td><nobr><b><tt id='l2h-4743' xml:id='l2h-4743' class="method">read</tt></b>(</nobr></td> | |
203 | <td><var></var><big>[</big><var>size</var><big>]</big><var></var>)</td></tr></table></dt> | |
204 | <dd> | |
205 | Read at most <var>size</var> bytes from the chunk (less if the read hits | |
206 | the end of the chunk before obtaining <var>size</var> bytes). If the | |
207 | <var>size</var> argument is negative or omitted, read all data until the | |
208 | end of the chunk. The bytes are returned as a string object. An | |
209 | empty string is returned when the end of the chunk is encountered | |
210 | immediately. | |
211 | </dl> | |
212 | ||
213 | <P> | |
214 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
215 | <td><nobr><b><tt id='l2h-4744' xml:id='l2h-4744' class="method">skip</tt></b>(</nobr></td> | |
216 | <td><var></var>)</td></tr></table></dt> | |
217 | <dd> | |
218 | Skip to the end of the chunk. All further calls to <tt class="method">read()</tt> | |
219 | for the chunk will return <code>''</code>. If you are not interested in the | |
220 | contents of the chunk, this method should be called so that the file | |
221 | points to the start of the next chunk. | |
222 | </dl> | |
223 | <BR><HR><H4>Footnotes</H4> | |
224 | <DL> | |
225 | <DT><A NAME="foot67687">... | |
226 | chunks.</A><A | |
227 | href="module-chunk.html#tex2html164"><SUP>14.1</SUP></A></DT> | |
228 | <DD>``EA IFF 85'' Standard for Interchange Format Files, | |
229 | Jerry Morrison, Electronic Arts, January 1985. | |
230 | ||
231 | </DD> | |
232 | </DL> | |
233 | <DIV CLASS="navigation"> | |
234 | <div class='online-navigation'> | |
235 | <p></p><hr /> | |
236 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
237 | <tr> | |
238 | <td class='online-navigation'><a rel="prev" title="14.5.2 Wave_write Objects" | |
239 | href="Wave-write-objects.html"><img src='../icons/previous.png' | |
240 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
241 | <td class='online-navigation'><a rel="parent" title="14. Multimedia Services" | |
242 | href="mmedia.html"><img src='../icons/up.png' | |
243 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
244 | <td class='online-navigation'><a rel="next" title="14.7 colorsys " | |
245 | href="module-colorsys.html"><img src='../icons/next.png' | |
246 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
247 | <td align="center" width="100%">Python Library Reference</td> | |
248 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
249 | href="contents.html"><img src='../icons/contents.png' | |
250 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
251 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
252 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
253 | <td class='online-navigation'><a rel="index" title="Index" | |
254 | href="genindex.html"><img src='../icons/index.png' | |
255 | border='0' height='32' alt='Index' width='32' /></A></td> | |
256 | </tr></table> | |
257 | <div class='online-navigation'> | |
258 | <b class="navlabel">Previous:</b> | |
259 | <a class="sectref" rel="prev" href="Wave-write-objects.html">14.5.2 Wave_write Objects</A> | |
260 | <b class="navlabel">Up:</b> | |
261 | <a class="sectref" rel="parent" href="mmedia.html">14. Multimedia Services</A> | |
262 | <b class="navlabel">Next:</b> | |
263 | <a class="sectref" rel="next" href="module-colorsys.html">14.7 colorsys </A> | |
264 | </div> | |
265 | </div> | |
266 | <hr /> | |
267 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
268 | </DIV> | |
269 | <!--End of Navigation Panel--> | |
270 | <ADDRESS> | |
271 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
272 | </ADDRESS> | |
273 | </BODY> | |
274 | </HTML> |