CsvItemExporter for multiple files in custom item pipeline not exporting all items

问题

I have created an item pipeline as an answer to this question.
It is supposed to create a new file for every page according to the page_no value set in the item. This works mostly fine.
The problem is with the last csv file generated by the pipeline/item exporter, page-10.csv.
The last 10 values are not exported, so the file stays empty. What could be the reason for this behaviour?

pipelines.py

from scrapy.exporters import CsvItemExporter

class PerFilenameExportPipeline:
    """Distribute items across multiple CSV files according to their 'page_no' field"""

    def open_spider(self, spider):
        self.filename_to_exporter = {}

    def spider_closed(self, spider):
        for exporter in self.filename_to_exporter.values():
            exporter.finish_exporting()

    def _exporter_for_item(self, item):
        filename = 'page-' + str(item['page_no'])
        del item['page_no']
        if filename not in self.filename_to_exporter:
            f = open(f'{filename}.csv', 'wb')
            exporter = CsvItemExporter(f, export_empty_fields=True)
            exporter.start_exporting()
            self.filename_to_exporter[filename] = exporter
        return self.filename_to_exporter[filename]

    def process_item(self, item, spider):
        exporter = self._exporter_for_item(item)
        exporter.export_item(item)
        return item

spider

import scrapy
from ..pipelines import PerFilenameExportPipeline


class spidey(scrapy.Spider):
    name = "idk"
    custom_settings = {
        'ITEM_PIPELINES': {
            PerFilenameExportPipeline: 100
        }
    }
    
    def start_requests(self):
        yield scrapy.Request("http://quotes.toscrape.com/", cb_kwargs={'page_no': 1})

    def parse(self, response, page_no):
        for qts in response.xpath("//*[@class=\"quote\"]"):
            yield {
                'page_no': page_no,
                'author' : qts.xpath("./span[2]/small/text()").get(),
                'quote' : qts.xpath("./*[@class=\"text\"]/text()").get()
            }

        next_pg = response.xpath('//li[@class="next"]/a/@href').get()      
        if next_pg is not None:
            yield response.follow(next_pg, cb_kwargs={'page_no': page_no + 1})

来源：https://stackoverflow.com/questions/65007869/csvitemexporter-for-multiple-files-in-custom-item-pipeline-not-exporting-all-ite