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POGetting erratic "Invalid Signal signature" errors in PySide QWebPage
 

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  1. POGetting erratic "Invalid Signal signature" errors in PySide QWebPage
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    <p>I am creating an application which automates loading webpages and creating screenshots (no, I cannot use one of the existing solutions) using PySide. One part of the app gets a list of URLs and loads each URL in turn using a <strong>new</strong> QWebPage object. After the page is loaded a screenshot is taken and the QWebPage object is deleted. </p> <p>Every now and then, given enough runs, I get the following error from PySide, as a RuntimeError exception:</p> <pre><code>Invalid Signal signature: loadStarted() Failed to connect signal loadStarted(). </code></pre> <p>The first line is printed to STDERR (probably by Qt?) and the second line is the Python exception. </p> <p>loadStarted() is a built-in QWebPage signal, not something I created. This works 90% of the time, and I could not figure out what makes it fail occasionally. </p> <p>To be honest, this app is quite unusual in design, as it hooks PySide/Qt into a uWSGI served web app - this means that for example I am not using the QApplication event loop but rather a local event loop for each page load. I am also not experienced in either Qt or Python so it's possible I'm making a lot of mistakes, but I can't figure out what those are. </p> <p>I am thinking <a href="https://stackoverflow.com/questions/7577290/pyside-signal-duplicating-behavior">this</a> post might have something to do with it, but I'm not sure. </p> <p>Any suggestions on where to look next? </p> <p><strong>UPDATE:</strong> the signal is connected through the following code: </p> <pre><code>class MyWebPage(QWebPage): def __init__(self, parent=None): super(MyWebPage, self).__init__(parent) self.loadStarted.connect(self.started) self.loadFinished[bool].connect(self.finished) </code></pre> <p>MyWebPage objects are created as children of a different single QObject instance which is not deleted until the process shuts down. They are deleted by calling page.deleteLater() once I am done with them. Since I am running a local event loop, I trigger deferred deletions to happen after exiting local event loop by calling:</p> <pre><code> # self.eventLoop is the local event loop, which at this stage is not running self.eventLoop.processEvents() # self.app is the QApplication instance self.app.sendPostedEvents(None, QEvent.DeferredDelete) </code></pre>
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    1. COHow are the signals being connected? What code are you using to ensure the webpage objects are being deleted properly? Have you tried to create a simplified test-case that reproduces the problem?
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    2. COI tried creating a simplified test case but so far couldn't - this is quite hard to reproduce as is. I've updated the question with some info which might help.
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    3. CODo you happen to have any multi-threading going on?
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