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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<head>
<title>The Python X Library: 4.2 CatchError</title>
<meta name="description" content="The Python X Library: 4.2 CatchError">
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<a name="CatchError"></a>
<table class="header" cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="python-xlib_6.html#Error-Handling" title="Beginning of this chapter or previous chapter"> << </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_7.html#X-Error-Classes" title="Previous section in reading order"> < </a>]</td>
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<hr>
<a name="CatchError-1"></a>
<h2 class="section">4.2 CatchError</h2>
<p><code>error.CatchError</code> is an object which can be used as an error
handler. It collects an error matching any of the specified types,
which can be retrieved later. If several errors occur, only the last
one is remembered.
</p>
<dl>
<dt><a name="index-CatchError"></a>Class: <strong>CatchError</strong><em> ( *errors )</em></dt>
<dd>
<p>Create a new error handler object. Initialize by providing all error
classes you are interested in as arguments. If no error classes are
provided at all, this means that all errors will be considered.
</p>
</dd></dl>
<p>Pass the <code>error.CatchError</code> object as the <code>onerror</code> parameter
to X object methods. If these methods generated any errors matching the
ones specified, it can be retrieved with the following functions:
</p>
<dl>
<dt><a name="index-get_005ferror-on-CatchError"></a>Method on CatchError: <strong>get_error</strong><em> ( )</em></dt>
<dd>
<p>Return the last error object caught, or None if no matching errors has
occured.
</p>
</dd></dl>
<dl>
<dt><a name="index-get_005frequest-on-CatchError"></a>Method on CatchError: <strong>get_request</strong><em> ( )</em></dt>
<dd>
<p>Return the request object for the last error caught, or None if no
matching errors has occured.
</p>
</dd></dl>
<p><code>error.CatchError</code> objects can be reused:
</p>
<dl>
<dt><a name="index-reset-on-CatchError"></a>Method on CatchError: <strong>reset</strong><em> ( )</em></dt>
<dd>
<p>Forget any caught error.
</p>
</dd></dl>
<p>Since the X protocol is mostly asynchronous any error we’re watching for
might not have been received when we call <code>get_error</code>. To make
sure that the request has been processed by the server and any error
generated has been received by the Xlib, we must synchronize with the
server.
</p>
<p>An example of using <code>error.CatchError</code>:
</p>
<div class="example">
<pre class="example"># Resize and the foo window
# If it has been destroyed since we looked at it the last time,
# reset variable foo to None
# Create a error handler for BadWindow errors
ec = error.CatchError(error.BadWindow)
# Perform the operation
foo.configure(width = 100, height = 200, onerror = ec)
# Sync communication with server
display.sync()
# And check if there was any error
if ec.get_error():
foo = None
</pre></div>
<hr>
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<tr><td valign="middle" align="left">[<a href="python-xlib_6.html#Error-Handling" title="Beginning of this chapter or previous chapter"> << </a>]</td>
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