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<H1><A NAME="SECTION00101300000000000000000">
8.13 <tt class="module">posixfile</tt> --
         File-like objects with locking support</A>
</H1>

<P>
<A NAME="module-posixfile"></A>  
<p class="availability">Availability: <span
 class="platform">Unix</span>.</p>

<P>
<a id='l2h-3040' xml:id='l2h-3040'></a>
<P>
<div class="versionnote"><b>Deprecated since release 1.5.</b>
The locking operation that this module provides is
done better and more portably by the
<tt class="function"><tt class="module"><a href="module-fcntl.html">fcntl</a></tt>.lockf()</tt> call.
<a id='l2h-3042' xml:id='l2h-3042'></a></div><p></p>

<P>
This module implements some additional functionality over the built-in
file objects.  In particular, it implements file locking, control over
the file flags, and an easy interface to duplicate the file object.
The module defines a new file object, the posixfile object.  It
has all the standard file object methods and adds the methods
described below.  This module only works for certain flavors of
<span class="Unix">Unix</span>, since it uses <tt class="function">fcntl.fcntl()</tt> for file locking.<a id='l2h-3044' xml:id='l2h-3044'></a>
<P>
To instantiate a posixfile object, use the <tt class="function">open()</tt> function
in the <tt class="module">posixfile</tt> module.  The resulting object looks and
feels roughly the same as a standard file object.

<P>
The <tt class="module">posixfile</tt> module defines the following constants:

<P>
<dl><dt><b><tt id='l2h-3045' xml:id='l2h-3045'>SEEK_SET</tt></b></dt>
<dd>
Offset is calculated from the start of the file.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-3046' xml:id='l2h-3046'>SEEK_CUR</tt></b></dt>
<dd>
Offset is calculated from the current position in the file.
</dd></dl>

<P>
<dl><dt><b><tt id='l2h-3047' xml:id='l2h-3047'>SEEK_END</tt></b></dt>
<dd>
Offset is calculated from the end of the file.
</dd></dl>

<P>
The <tt class="module">posixfile</tt> module defines the following functions:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3048' xml:id='l2h-3048' class="function">open</tt></b>(</nobr></td>
  <td><var>filename</var><big>[</big><var>, mode</var><big>[</big><var>, bufsize</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
 Create a new posixfile object with the given filename and mode.  The
 <var>filename</var>, <var>mode</var> and <var>bufsize</var> arguments are
 interpreted the same way as by the built-in <tt class="function">open()</tt>
 function.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3049' xml:id='l2h-3049' class="function">fileopen</tt></b>(</nobr></td>
  <td><var>fileobject</var>)</td></tr></table></dt>
<dd>
 Create a new posixfile object with the given standard file object.
 The resulting object has the same filename and mode as the original
 file object.
</dl>

<P>
The posixfile object defines the following additional methods:

<P>

<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3050' xml:id='l2h-3050' class="function">lock</tt></b>(</nobr></td>
  <td><var>fmt, </var><big>[</big><var>len</var><big>[</big><var>, start</var><big>[</big><var>, whence</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
 Lock the specified section of the file that the file object is
 referring to.  The format is explained
 below in a table.  The <var>len</var> argument specifies the length of the
 section that should be locked. The default is <code>0</code>. <var>start</var>
 specifies the starting offset of the section, where the default is
 <code>0</code>.  The <var>whence</var> argument specifies where the offset is
 relative to. It accepts one of the constants <tt class="constant">SEEK_SET</tt>,
 <tt class="constant">SEEK_CUR</tt> or <tt class="constant">SEEK_END</tt>.  The default is
 <tt class="constant">SEEK_SET</tt>.  For more information about the arguments refer
 to the <span class="manpage"><i>fcntl</i>(2)</span> manual page on your system.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3051' xml:id='l2h-3051' class="function">flags</tt></b>(</nobr></td>
  <td><var></var><big>[</big><var>flags</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
 Set the specified flags for the file that the file object is referring
 to.  The new flags are ORed with the old flags, unless specified
 otherwise.  The format is explained below in a table.  Without
 the <var>flags</var> argument
 a string indicating the current flags is returned (this is
 the same as the "<tt class="samp">?</tt>" modifier).  For more information about the
 flags refer to the <span class="manpage"><i>fcntl</i>(2)</span> manual page on your system.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3052' xml:id='l2h-3052' class="function">dup</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
 Duplicate the file object and the underlying file pointer and file
 descriptor.  The resulting object behaves as if it were newly
 opened.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3053' xml:id='l2h-3053' class="function">dup2</tt></b>(</nobr></td>
  <td><var>fd</var>)</td></tr></table></dt>
<dd>
 Duplicate the file object and the underlying file pointer and file
 descriptor.  The new object will have the given file descriptor.
 Otherwise the resulting object behaves as if it were newly opened.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3054' xml:id='l2h-3054' class="function">file</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
 Return the standard file object that the posixfile object is based
 on.  This is sometimes necessary for functions that insist on a
 standard file object.
</dl>

<P>
All methods raise <tt class="exception">IOError</tt> when the request fails.

<P>
Format characters for the <tt class="method">lock()</tt> method have the following
meaning:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="center">Format</th>
      <th class="left"  >Meaning</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="center" valign="baseline"><samp>u</samp></td>
        <td class="left"  >unlock the specified region</td></tr>
    <tr><td class="center" valign="baseline"><samp>r</samp></td>
        <td class="left"  >request a read lock for the specified section</td></tr>
    <tr><td class="center" valign="baseline"><samp>w</samp></td>
        <td class="left"  >request a write lock for the specified section</td></tr></tbody>
</table></div>

<P>
In addition the following modifiers can be added to the format:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="center">Modifier</th>
      <th class="left"  >Meaning</th>
      <th class="center">Notes</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="center" valign="baseline"><samp>|</samp></td>
        <td class="left"  >wait until the lock has been granted</td>
        <td class="center"></td></tr>
    <tr><td class="center" valign="baseline"><samp>?</samp></td>
        <td class="left"  >return the first lock conflicting with the requested lock, or
              <code>None</code> if there is no conflict.</td>
        <td class="center">(1)</td></tr></tbody>
</table></div>

<P>
Note:

<P>
<DL>
<DT><STRONG>(1)</STRONG></DT>
<DD>The lock returned is in the format <code>(<var>mode</var>, <var>len</var>,
<var>start</var>, <var>whence</var>, <var>pid</var>)</code> where <var>mode</var> is a character
representing the type of lock ('r' or 'w').  This modifier prevents a
request from being granted; it is for query purposes only.
</DD>
</DL>

<P>
Format characters for the <tt class="method">flags()</tt> method have the following
meanings:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="center">Format</th>
      <th class="left"  >Meaning</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="center" valign="baseline"><samp>a</samp></td>
        <td class="left"  >append only flag</td></tr>
    <tr><td class="center" valign="baseline"><samp>c</samp></td>
        <td class="left"  >close on exec flag</td></tr>
    <tr><td class="center" valign="baseline"><samp>n</samp></td>
        <td class="left"  >no delay flag (also called non-blocking flag)</td></tr>
    <tr><td class="center" valign="baseline"><samp>s</samp></td>
        <td class="left"  >synchronization flag</td></tr></tbody>
</table></div>

<P>
In addition the following modifiers can be added to the format:

<P>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="center">Modifier</th>
      <th class="left"  >Meaning</th>
      <th class="center">Notes</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="center" valign="baseline"><samp>!</samp></td>
        <td class="left"  >turn the specified flags 'off', instead of the default 'on'</td>
        <td class="center">(1)</td></tr>
    <tr><td class="center" valign="baseline"><samp>=</samp></td>
        <td class="left"  >replace the flags, instead of the default 'OR' operation</td>
        <td class="center">(1)</td></tr>
    <tr><td class="center" valign="baseline"><samp>?</samp></td>
        <td class="left"  >return a string in which the characters represent the flags that
  are set.</td>
        <td class="center">(2)</td></tr></tbody>
</table></div>

<P>
Notes:

<P>
<DL>
<DT><STRONG>(1)</STRONG></DT>
<DD>The "<tt class="samp">!</tt>" and "<tt class="samp">=</tt>" modifiers are mutually exclusive.

<P>
</DD>
<DT><STRONG>(2)</STRONG></DT>
<DD>This string represents the flags after they may have been altered
by the same call.
</DD>
</DL>

<P>
Examples:

<P>
<div class="verbatim"><pre>
import posixfile

file = posixfile.open('/tmp/test', 'w')
file.lock('w|')
...
file.lock('u')
file.close()
</pre></div>

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	54
	55	<H1><A NAME="SECTION00101300000000000000000">
	56	8.13 <tt class="module">posixfile</tt> --
	57	File-like objects with locking support</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-posixfile"></A>
	62	<p class="availability">Availability: <span
	63	class="platform">Unix</span>.</p>
	64
65	<P>
66	<a id='l2h-3040' xml:id='l2h-3040'></a>
67	<P>
68	<div class="versionnote"><b>Deprecated since release 1.5.</b>
69	The locking operation that this module provides is
70	done better and more portably by the
71	<tt class="function"><tt class="module"><a href="module-fcntl.html">fcntl</a></tt>.lockf()</tt> call.
72	<a id='l2h-3042' xml:id='l2h-3042'></a></div><p></p>
73
74	<P>
75	This module implements some additional functionality over the built-in
76	file objects. In particular, it implements file locking, control over
77	the file flags, and an easy interface to duplicate the file object.
78	The module defines a new file object, the posixfile object. It
79	has all the standard file object methods and adds the methods
80	described below. This module only works for certain flavors of
81	<span class="Unix">Unix</span>, since it uses <tt class="function">fcntl.fcntl()</tt> for file locking.<a id='l2h-3044' xml:id='l2h-3044'></a>
82	<P>
83	To instantiate a posixfile object, use the <tt class="function">open()</tt> function
84	in the <tt class="module">posixfile</tt> module. The resulting object looks and
85	feels roughly the same as a standard file object.
86
87	<P>
88	The <tt class="module">posixfile</tt> module defines the following constants:
89
90	<P>
91	<dl><dt><b><tt id='l2h-3045' xml:id='l2h-3045'>SEEK_SET</tt></b></dt>
92	<dd>
93	Offset is calculated from the start of the file.
94	</dd></dl>
95
96	<P>
97	<dl><dt><b><tt id='l2h-3046' xml:id='l2h-3046'>SEEK_CUR</tt></b></dt>
98	<dd>
99	Offset is calculated from the current position in the file.
100	</dd></dl>
101
102	<P>
103	<dl><dt><b><tt id='l2h-3047' xml:id='l2h-3047'>SEEK_END</tt></b></dt>
104	<dd>
105	Offset is calculated from the end of the file.
106	</dd></dl>
107
108	<P>
109	The <tt class="module">posixfile</tt> module defines the following functions:
110
111	<P>
112	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
113	<td><nobr><b><tt id='l2h-3048' xml:id='l2h-3048' class="function">open</tt></b>(</nobr></td>
114	<td><var>filename</var><big>[</big><var>, mode</var><big>[</big><var>, bufsize</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
115	<dd>
116	Create a new posixfile object with the given filename and mode. The
117	<var>filename</var>, <var>mode</var> and <var>bufsize</var> arguments are
118	interpreted the same way as by the built-in <tt class="function">open()</tt>
119	function.
120	</dl>
121
122	<P>
123	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
124	<td><nobr><b><tt id='l2h-3049' xml:id='l2h-3049' class="function">fileopen</tt></b>(</nobr></td>
125	<td><var>fileobject</var>)</td></tr></table></dt>
126	<dd>
127	Create a new posixfile object with the given standard file object.
128	The resulting object has the same filename and mode as the original
129	file object.
130	</dl>
131
132	<P>
133	The posixfile object defines the following additional methods:
134
135	<P>
136
137	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
138	<td><nobr><b><tt id='l2h-3050' xml:id='l2h-3050' class="function">lock</tt></b>(</nobr></td>
139	<td><var>fmt, </var><big>[</big><var>len</var><big>[</big><var>, start</var><big>[</big><var>, whence</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
140	<dd>
141	Lock the specified section of the file that the file object is
142	referring to. The format is explained
143	below in a table. The <var>len</var> argument specifies the length of the
144	section that should be locked. The default is <code>0</code>. <var>start</var>
145	specifies the starting offset of the section, where the default is
146	<code>0</code>. The <var>whence</var> argument specifies where the offset is
147	relative to. It accepts one of the constants <tt class="constant">SEEK_SET</tt>,
148	<tt class="constant">SEEK_CUR</tt> or <tt class="constant">SEEK_END</tt>. The default is
149	<tt class="constant">SEEK_SET</tt>. For more information about the arguments refer
150	to the <span class="manpage"><i>fcntl</i>(2)</span> manual page on your system.
151	</dl>
152
153	<P>
154	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
155	<td><nobr><b><tt id='l2h-3051' xml:id='l2h-3051' class="function">flags</tt></b>(</nobr></td>
156	<td><var></var><big>[</big><var>flags</var><big>]</big><var></var>)</td></tr></table></dt>
157	<dd>
158	Set the specified flags for the file that the file object is referring
159	to. The new flags are ORed with the old flags, unless specified
160	otherwise. The format is explained below in a table. Without
161	the <var>flags</var> argument
162	a string indicating the current flags is returned (this is
163	the same as the "<tt class="samp">?</tt>" modifier). For more information about the
164	flags refer to the <span class="manpage"><i>fcntl</i>(2)</span> manual page on your system.
165	</dl>
166
167	<P>
168	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
169	<td><nobr><b><tt id='l2h-3052' xml:id='l2h-3052' class="function">dup</tt></b>(</nobr></td>
170	<td><var></var>)</td></tr></table></dt>
171	<dd>
172	Duplicate the file object and the underlying file pointer and file
173	descriptor. The resulting object behaves as if it were newly
174	opened.
175	</dl>
176
177	<P>
178	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
179	<td><nobr><b><tt id='l2h-3053' xml:id='l2h-3053' class="function">dup2</tt></b>(</nobr></td>
180	<td><var>fd</var>)</td></tr></table></dt>
181	<dd>
182	Duplicate the file object and the underlying file pointer and file
183	descriptor. The new object will have the given file descriptor.
184	Otherwise the resulting object behaves as if it were newly opened.
185	</dl>
186
187	<P>
188	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
189	<td><nobr><b><tt id='l2h-3054' xml:id='l2h-3054' class="function">file</tt></b>(</nobr></td>
190	<td><var></var>)</td></tr></table></dt>
191	<dd>
192	Return the standard file object that the posixfile object is based
193	on. This is sometimes necessary for functions that insist on a
194	standard file object.
195	</dl>
196
197	<P>
198	All methods raise <tt class="exception">IOError</tt> when the request fails.
199
200	<P>
201	Format characters for the <tt class="method">lock()</tt> method have the following
202	meaning:
203
204	<P>
205	<div class="center"><table class="realtable">
206	<thead>
207	<tr>
208	<th class="center">Format</th>
209	<th class="left" >Meaning</th>
210	</tr>
211	</thead>
212	<tbody>
213	<tr><td class="center" valign="baseline"><samp>u</samp></td>
214	<td class="left" >unlock the specified region</td></tr>
215	<tr><td class="center" valign="baseline"><samp>r</samp></td>
216	<td class="left" >request a read lock for the specified section</td></tr>
217	<tr><td class="center" valign="baseline"><samp>w</samp></td>
218	<td class="left" >request a write lock for the specified section</td></tr></tbody>
219	</table></div>
220
221	<P>
222	In addition the following modifiers can be added to the format:
223
224	<P>
225	<div class="center"><table class="realtable">
226	<thead>
227	<tr>
228	<th class="center">Modifier</th>
229	<th class="left" >Meaning</th>
230	<th class="center">Notes</th>
231	</tr>
232	</thead>
233	<tbody>
234	<tr><td class="center" valign="baseline"><samp>\|</samp></td>
235	<td class="left" >wait until the lock has been granted</td>
236	<td class="center"></td></tr>
237	<tr><td class="center" valign="baseline"><samp>?</samp></td>
238	<td class="left" >return the first lock conflicting with the requested lock, or
239	<code>None</code> if there is no conflict.</td>
240	<td class="center">(1)</td></tr></tbody>
241	</table></div>
242
243	<P>
244	Note:
245
246	<P>
247	<DL>
248	<DT><STRONG>(1)</STRONG></DT>
249	<DD>The lock returned is in the format <code>(<var>mode</var>, <var>len</var>,
250	<var>start</var>, <var>whence</var>, <var>pid</var>)</code> where <var>mode</var> is a character
251	representing the type of lock ('r' or 'w'). This modifier prevents a
252	request from being granted; it is for query purposes only.
253	</DD>
254	</DL>
255
256	<P>
257	Format characters for the <tt class="method">flags()</tt> method have the following
258	meanings:
259
260	<P>
261	<div class="center"><table class="realtable">
262	<thead>
263	<tr>
264	<th class="center">Format</th>
265	<th class="left" >Meaning</th>
266	</tr>
267	</thead>
268	<tbody>
269	<tr><td class="center" valign="baseline"><samp>a</samp></td>
270	<td class="left" >append only flag</td></tr>
271	<tr><td class="center" valign="baseline"><samp>c</samp></td>
272	<td class="left" >close on exec flag</td></tr>
273	<tr><td class="center" valign="baseline"><samp>n</samp></td>
274	<td class="left" >no delay flag (also called non-blocking flag)</td></tr>
275	<tr><td class="center" valign="baseline"><samp>s</samp></td>
276	<td class="left" >synchronization flag</td></tr></tbody>
277	</table></div>
278
279	<P>
280	In addition the following modifiers can be added to the format:
281
282	<P>
283	<div class="center"><table class="realtable">
284	<thead>
285	<tr>
286	<th class="center">Modifier</th>
287	<th class="left" >Meaning</th>
288	<th class="center">Notes</th>
289	</tr>
290	</thead>
291	<tbody>
292	<tr><td class="center" valign="baseline"><samp>!</samp></td>
293	<td class="left" >turn the specified flags 'off', instead of the default 'on'</td>
294	<td class="center">(1)</td></tr>
295	<tr><td class="center" valign="baseline"><samp>=</samp></td>
296	<td class="left" >replace the flags, instead of the default 'OR' operation</td>
297	<td class="center">(1)</td></tr>
298	<tr><td class="center" valign="baseline"><samp>?</samp></td>
299	<td class="left" >return a string in which the characters represent the flags that
300	are set.</td>
301	<td class="center">(2)</td></tr></tbody>
302	</table></div>
303
304	<P>
305	Notes:
306
307	<P>
308	<DL>
309	<DT><STRONG>(1)</STRONG></DT>
310	<DD>The "<tt class="samp">!</tt>" and "<tt class="samp">=</tt>" modifiers are mutually exclusive.
311
312	<P>
313	</DD>
314	<DT><STRONG>(2)</STRONG></DT>
315	<DD>This string represents the flags after they may have been altered
316	by the same call.
317	</DD>
318	</DL>
319
320	<P>
321	Examples:
322
323	<P>
324	<div class="verbatim"><pre>
325	import posixfile
326
327	file = posixfile.open('/tmp/test', 'w')
328	file.lock('w\|')
329	...
330	file.lock('u')
331	file.close()
332	</pre></div>
333
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