GeezerVison is showing github.com — gh-131178: Fix test_cli_retrieve_file when stdout is StringIO in test_ftplib by rudy-07 · Pull Request #161135 · python/cpython
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rudy-07
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Nov 1, 2026
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In #161080, test_cli_retrieve_file was added to Lib/test/test_ftplib.py. In ftplib.test(), file retrieval calls ftp.retrbinary('RETR ' + file, sys.stdout.buffer.write, 1024) and sys.stdout.buffer.flush().
When tests run under regrtest on buildbots, sys.stdout is wrapped in an io.StringIO instance which lacks a .buffer attribute, causing AttributeError: '_io.StringIO' object has no attribute 'buffer'.
This patch mocks sys.stdout in CommandLineTest.test_cli_retrieve_file to prevent the error and assert the callback and flush calls.
Follow-up to #161080.
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Mock sys.stdout in CommandLineTest.test_cli_retrieve_file so that
accessing sys.stdout.buffer does not fail when regrtest or other test
runners wrap sys.stdout in an io.StringIO object.
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giampaolo
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