How to Efficiently Retrieve Multiple URLs Using QWebPage in Qt?

Retrieve Multiple URLs with QWebPage

In this scenario, you've attempted to use Qt's QWebPage to render dynamically updated pages. However, you've encountered frequent crashes upon attempting to render a second page.

Problem Analysis

The issue lies in your approach. You're initializing a new QApplication and QWebPage for each URL fetch. Instead, it's recommended to maintain a single QApplication and QWebPage, using signals and custom processing to handle multiple URLs within the same instance.

Proposed Solution

WebPage Class

Below are custom WebPage classes for both PyQt5 and PyQt4:

PyQt5 WebPage

<code class="python">from PyQt5.QtCore import pyqtSignal, QUrl
from PyQt5.QtWidgets import QApplication
from PyQt5.QtWebEngineWidgets import QWebEnginePage

class WebPage(QWebEnginePage):
    htmlReady = pyqtSignal(str, str)

    def __init__(self, verbose=False):
        super().__init__()
        self._verbose = verbose
        self.loadFinished.connect(self.handleLoadFinished)

    def process(self, urls):
        self._urls = iter(urls)
        self.fetchNext()

    def fetchNext(self):
        try:
            url = next(self._urls)
        except StopIteration:
            return False
        else:
            self.load(QUrl(url))
        return True

    def processCurrentPage(self, html):
        self.htmlReady.emit(html, self.url().toString())
        if not self self.fetchNext():
            QApplication.instance().quit()

    def handleLoadFinished(self):
        self.toHtml(self.processCurrentPage)

    def javaScriptConsoleMessage(self, *args, **kwargs):
        if self._verbose:
            super().javaScriptConsoleMessage(*args, **kwargs)</code>

PyQt4 WebPage

<code class="python">from PyQt4.QtCore import pyqtSignal, QUrl
from PyQt4.QtGui import QApplication
from PyQt4.QtWebKit import QWebPage

class WebPage(QWebPage):
    htmlReady = pyqtSignal(str, str)

    def __init__(self, verbose=False):
        super(WebPage, self).__init__()
        self._verbose = verbose
        self.mainFrame().loadFinished.connect(self.handleLoadFinished)

    def process(self, urls):
        self._urls = iter(urls)
        self.fetchNext()

    def fetchNext(self):
        try: 
            url = next(self._urls)
        except StopIteration:
            return False
        else:
            self.mainFram().load(QUrl(url))
        return True

    def processCurrentPage(self):
        self.htmlReady.emit(self.mainFrame().toHtml(), self.mainFrame().url().toString())
        if not self.fetchNext():
            QApplication.instance().quit()

    def javaScripConsoleMessage(self ,* args, **kwargs):
        if self._verbose:
            super(WebPage, self).javaScriptConsoleMessage(*args, **kwargs)</code>

Usage

Here's an example of how to use these WebPage classes:

<code class="python">from PyQt5.QtCore import QUrl
from PyQt5.QtWidgets import QApplication

# PyQt5
url_list = ['https://example.com', 'https://example2.com']
app = QApplication(sys.argv)
webpage = WebPage(verbose=True)
webpage.htmlReady.connect(my_html_processor)
webpage.process(url_list)
sys.exit(app.exec_())

# PyQt4
from PyQt4.QtCore import QUrl
from PyQt4.QtGui import QApplication
url_list = ['https://example.com', 'https://example2.com']
app = QApplication(sys.argv)
webpage = WebPage(verbose=True)
webpage.htmlReady.connect(my_html_processor)
webpage.process(url_list)
sys.exit(app.exec_())</code>

In this code, my_html_processor is a function that can be customized to handle the processed HTML and URL information for each page.

By implementing this approach, you can prevent the crashes and random behavior you previously experienced, resulting in a more stable and efficient web scraping workflow.

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