Why does calling a scrapy spider from pywikibot give a ReactorNotRestartable error? - scrapy

Question

I am able to call a scrapy spider from another Python script using either CrawlerRunner or CrawlerProcess. But, when I try to call the same spider calling class from a pywikibot robot, I get a ReactorNotRestartable error. Why is this and how can I fix it?
Here is the error:
File ".\scripts\userscripts\ReplicationWiki\RWLoad.py", line 161, in format_new_page
aea = AEAMetadata(url=DOI_url)
File ".\scripts\userscripts\ReplicationWiki\GetAEAMetadata.py", line 39, in __init__
reactor.run() # the script will block here until all crawling jobs are finished
File "C:\Users\lextr\.conda\envs\py37\lib\site-packages\twisted\internet\base.py", line 1282, in run
self.startRunning(installSignalHandlers=installSignalHandlers)
File "C:\Users\lextr\.conda\envs\py37\lib\site-packages\twisted\internet\base.py", line 1262, in startRunning
ReactorBase.startRunning(self)
File "C:\Users\lextr\.conda\envs\py37\lib\site-packages\twisted\internet\base.py", line 765, in startRunning
raise error.ReactorNotRestartable()
twisted.internet.error.ReactorNotRestartable
CRITICAL: Exiting due to uncaught exception <class 'twisted.internet.error.ReactorNotRestartable'>
Here is the script which calls my scrapy spider. It runs fine if I just call the class from main.
from twisted.internet import reactor, defer
from scrapy import signals
from scrapy.crawler import Crawler, CrawlerProcess, CrawlerRunner
from scrapy.settings import Settings
from scrapy.utils.project import get_project_settings
from Scrapers.spiders.ScrapeAEA import ScrapeaeaSpider
class AEAMetadata:
"""
Helper to run ScrapeAEA spider and return JEL codes and data links
for a given AEA article link.
"""
def __init__(self, *args, **kwargs):
"""Initializer"""
url = kwargs.get('url')
if not url:
raise ValueError('No article url given')
self.items = []
def collect_items(item, response, spider):
self.items.append(item)
settings = get_project_settings()
crawler = Crawler(ScrapeaeaSpider, settings)
crawler.signals.connect(collect_items, signals.item_scraped)
runner = CrawlerRunner(settings)
d = runner.crawl(crawler, url=url)
d.addBoth(lambda _: reactor.stop())
reactor.run() # the script will block here until all crawling jobs are finished
#process = CrawlerProcess(settings)
#process.crawl(crawler, url=url)
#process.start() # the script will block here until the crawling is finished
def get_jelcodes(self):
jelcodes = self.items[0]['jelcodes']
return jelcodes
def main():
aea = AEAMetadata(url='https://doi.org/10.1257/app.20180286')
jelcodes = aea.get_jelcodes()
print(jelcodes)
if __name__ == '__main__':
main()
Updated simple Test that instantiates the AEAMetadata class twice.
Here is the calling code in my pywikibot bot which fails:
from GetAEAMetadata import AEAMetadata
def main(*args):
for _ in [1,2]:
print('Top')
url = 'https://doi.org/10.1257/app.20170442'
aea = AEAMetadata(url=url)
print('After AEAMetadata')
jelcodes = aea.get_jelcodes()
print(jelcodes)
if __name__ == '__main__':
main()

Answer 1

My call to AEAMetadata was embedded in a larger script which fooled me into thinking the AEAMetadata class was only instantiated once before failure.
In fact, AEAMetadata was called twice.
And, I also thought that the script would block after the reactor.run() because the comment in all the scrapy examples stated that was the case.
However, the second deferred callback is reactor.stop() which unblocks the reactor.run().
A more basic incorrect assumption was that the reactor was deleted and recreated on each iteration. In fact, the reactor is instantiated and initialized when it is first imported. And, it is a global object which lives as long as the underlying process and was not designed to be restarted. The extremes actually needed to delete and restart a reactor are described here:
http://www.blog.pythonlibrary.org/2016/09/14/restarting-a-twisted-reactor/
So, I guess I've answered my own question.
And, I'm rewriting my script so it doesn't try to use the reactor in a way it was never intended to be used.
And, thanks Gallaecio for getting me thinking in the right direction.