How do I make Python, QT, and Webkit work on a headless server?

Question

I have Debian Linux server that I use for a variety of things. I want it to be able to do some web-scraping jobs I need done regularly.

This code can be found here.

import sys  
from PyQt4.QtGui import *  
from PyQt4.QtCore import *  
from PyQt4.QtWebKit import *  

class Render(QWebPage):  
  def __init__(self, url):  
    self.app = QApplication(sys.argv, False)  # Line updated based on mata's answer
    QWebPage.__init__(self)  
    self.loadFinished.connect(self._loadFinished)  
    self.mainFrame().load(QUrl(url))  
    self.app.exec_()  

  def _loadFinished(self, result):  
    self.frame = self.mainFrame()  
    self.app.quit()  

A simple test of it would look like this:

url = 'http://example.com'
print Render(url).frame.toHtml()

On the call to the constructor it dies with this message (it's printed to stdout, not an uncaught exception).

: cannot connect to X server 

How can I use Python (2.7), QT4, and Webkit on a headless server? Nothing ever needs to be displayed, so I can tweek any settings or anything that need to be tweeked.

I've looked into alternatives, but this is the best fit for me and my projects. If I did have to install an X server, how could I do it with minimal overhead?

Answer 1

One of the constructors of QApplication takes a boolean argument GUIenabled.
If you use that, you can instantiante QAppliaction without an X server, but you can't create QWidgets.

So in this case the only option is to use a virtual X server like Xvfb to render the GUI.

Xvfb can be installed and run using these commands (assuming you have apt-get installed). The code in the original question is in a file called render.py.

sudo apt-get install xvfb
xvfb-run python render.py

Answer 2

If PyQt5 is an option, Qt 5 has the "minimal" platform plugin.

To use it, modify the argv passed to QApplication to include ['-platform', 'minimal'].

Answer 3

If all you are trying to do is get the webpage, you could use

import urllib
urllib.urlopen('http://example.com').read()

Answer 4

phantomjs is a webkit based solution. runs headless as well. try it out.

If you are keen on using webkit yourself you could also try the pyslide version of qt.

Answer 5

On gitlab CI/CD. Adding ['-platform', 'minimal'] and using xvfb didn't work for me. Instead I use QT_QPA_PLATFORM: "offscreen" variable.

See https://stackoverflow.com/a/55442821/6000005