[PyQt] PyQt5 and Spyder 3.3.2 Conflict, Beautiful Soup, <kernel died, restarting>

[Kyle Altendorf]

I don't believe your code guarantees that app.quit() gets called. But 
I'm a bit vague on the details myself.  I would start by adding a print 
before the quit call and then see if the failures to run a second time 
in the same kernel correspond to cases where the print doesn't happen.  
I would also rework it to avoid the inheritance.  Not because 
inheritance is evil but because it serves no purpose here if I am 
reading correctly.

Is the qt application even meant to be used twice?  It's a very global 
thing.  Might want to app = QApplication.instance() and then if that's 
none create an app for scenarios where you have a long-running 
interpreter.  Though the multi-use of it is even more of a concern then. 
  Do read the docs carefully about having multiple or reused app 
instances.  I think that's bad.

Maybe a side note, maybe not.  There's selenium and requests-html if you 
are just looking for a js-capable url getter/processor.

Cheers,
-kyle


On March 24, 2019 1:29:51 PM EDT, Gene Ensor <g_ensor at hotmail.com> 
wrote:
> Kyle,
> 
> Many thanks for your response!  However your questions are many levels
> above my head.  Please note I would be more than happy to run code and
> report on the output to you or the pseudo forum in an effort to move
> forward.  Additional information as follows:
> 
> On a second run I get:
> 
> <kernel died, restarting>
> or
> <An error occurred while starting the kernel>
> 
> Anaconda "Python 3.7.1 64-bit | Qt 5.9.6 | PyQt5 5.9.2 | Windows 10 |
> Spyder 3.3.2
> 
> Spyder>help>dependencies
> 
> IPython >=4.0     :  7.2.0 (OK)
> cython >=0.21     :  0.29.2 (OK)
> jedi >=0.9.0      :  0.13.2 (OK)
> matplotlib >=2.0.0:  3.0.2 (OK)
> nbconvert >=4.0   :  5.4.0 (OK)
> numpy >=1.7       :  1.15.4 (OK)
> pandas >=0.13.1   :  0.23.4 (OK)
> pycodestyle >=2.3 :  2.4.0 (OK)
> pyflakes >=0.6.0  :  2.0.0 (OK)
> pygments >=2.0    :  2.3.1 (OK)
> pylint >=0.25     :  2.2.2 (OK)
> qtconsole >=4.2.0 :  4.4.3 (OK)
> rope >=0.9.4      :  0.11.0 (OK)
> sphinx >=0.6.6    :  1.8.2 (OK)
> sympy >=0.7.3     :  1.3 (OK)
> 
> Thanks again!
> 
> Gene
> 
> -----Original Message-----
> From: Kyle Altendorf <sda at fstab.net>
> Sent: Saturday, March 23, 2019 7:59 PM
> To: pyqt at riverbankcomputing.com; Gene Ensor <g_ensor at hotmail.com>;
> pyqt at riverbankcomputing.com
> Subject: Re: [PyQt] PyQt5 and Spyder 3.3.2 Conflict, Beautiful Soup,
> <An error occurred while starting the kernel>
> 
> Have you verified in those cases that the app exit is being called?  If
> you fail out because of an exception it won't be.  I would really
> manage the app outside your class.  (Does Qt really force you to
> inherit here?). Then you can try/finally to make sure it gets exited
> even after a python exception.  Or even make yourself a context
> manager.
> 
> Cheers,
> -kyle
> 
> On March 23, 2019 9:28:13 PM EDT, Gene Ensor <g_ensor at hotmail.com>
> wrote:
>> Team,
>> 
>> Per
>> 
>> https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithu
>> b.com%2Fspyder-ide%2Fspyder%2Fwiki%2FHow-to-run-PyQt-applications-withi
>> n-Spyder&data=02%7C01%7C%7Cefe8a2de6a6a456bbd4708d6affc3ef3%7C84df9
>> e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636889895249156064&sdata=kKve
>> zNdJY%2BYL2%2F4Yjyq%2BQLdN%2BgtR%2BVyRRwK8vADUi0I%3D&reserved=0
>> 
>> I believe I have the following problem:
>> 
>> "The most common problem when running a PyQt multiple times inside
>> Spyder is that a QApplication instance remains in the namespace of the
> 
>> IPython console kernel after the first run. In other words, when you
>> try to re-run your application, you already have a QApplication
>> instance initialized."
>> 
>> Hence when ran a second time I get "An error occurred while starting
>> the kernel".  However I am not skilled enough to update the below code
> 
>> to behave correctly my environment.
>> 
>> Anaconda "Python 3.7.1 64-bit | Qt 5.9.6 | PyQt5 5.9.2 | Windows 10 |
>> Spyder 3.3.2
>> 
>> Can you assist?  Thanks!
>> 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> import sys
>> from PyQt5.QtWebEngineWidgets import QWebEnginePage from
>> PyQt5.QtWidgets import QApplication, QDialog from PyQt5.QtCore import
>> QUrl, QCoreApplication
>> 
>> import bs4 as bs
>> import urllib.request
>> 
>> 
>> class Page(QWebEnginePage):
>>    def __init__(self, url):
>> #       PyQt5 has the "minimal" platform plugin.
>> #       To use it, modify the argv passed to QApplication to include
>> #       ['-platform', 'minimal'].
>>        self.app = QApplication(sys.argv)
>>        QWebEnginePage.__init__(self)
>>        self.html = ''
>>        self.loadFinished.connect(self._on_load_finished)
>>        self.load(QUrl(url))
>>        self.app.exec_()
>> 
>>    def _on_load_finished(self):
>>        self.html = self.toHtml(self.Callable)
>>        print('Load finished')
>> 
>>    def Callable(self, html_str):
>>        self.html = html_str
>>        self.app.quit()
>> 
>> 
>> def main():
>>    page =
> Page('https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpythonprogramming.net%2Fparsememcparseface%2F&data=02%7C01%7C%7Cefe8a2de6a6a456bbd4708d6affc3ef3%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636889895249156064&sdata=uuqunuxYJs1xxShwscoSbBVf%2Bb1Su6A2l5zn%2FhCBsK8%3D&reserved=0')
>>    soup = bs.BeautifulSoup(page.html, 'html.parser')
>>    js_test = soup.find('p', class_='jstest')
>>    print(js_test.text)    #fixed
>>    # output should be "Look at you shinin!"
>> if __name__ == '__main__': main()
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~