`ValueError: I/O operation on closed file` when parsing feeds with leading newline in multiprocessing

[Alvaro-Kothe]

When parsing an RSS feed string that starts with a newline before the XML declaration inside a ProcessPoolExecutor, feedparser.parse returns a FeedParserDict object that cannot be pickled without raising:

ValueError: I/O operation on closed file

This error happens during the result pickling step after the worker finishes, not directly inside feedparser.parse.

Minimal Reproducible Example

import feedparser
from concurrent.futures import ProcessPoolExecutor

FEED_STR = """
<?xml version='1.0' encoding='UTF-8'?>
<rss version="2.0">
<channel>
<title>Foo</title>
<link>https://foo.com/</link>
<item><title>Title 1</title><link>https://foo.com/1</link><pubDate>Thu, 05 Jun 2025 18:27:58 -0000</pubDate></item>
</channel>
</rss>
"""

def parse_and_return_full(raw_feed: str):
    return feedparser.parse(raw_feed)

if __name__ == "__main__":
    with ProcessPoolExecutor() as pool:
        future = pool.submit(parse_and_return_full, FEED_STR)
        result = future.result()

Removing the initial newline from FEED_STR prevents the error.