Python's test suite hastest.support.captured_std* utilities to temporarily swapsys.std* with anio.StringIO(). These wrapper functions are used at least 240 times throughout the tests. A few greps¹ show quite a few instances where these helpers could be used but are not (45 usecontextlib.redirect_std*, 30 usetest.support.captured_output("std*"), and 15 use a manual solution).

Should we update these calls to use thesupport utilities to improve consistency or is it not worth the risk of accidentally changing a test's meaning and cluttering git blame? I found31d1d72 from last year which did similar updating intest_pydoc/test_pydoc.py. There's also an argument the "update" should go fromtest.support.captured_std* to the newercontextlib.redirect_std* instead, and remove the testing specific utilities.

Since this touches a wide range of domains, my thought was to split this up into separate PRs for each test file so the appropriate person can more easily review. But we can also do this in larger chunks, at least for the lower risk changes.

Instances ofcontextlib.redirect_std* swappable fortest.support.captured_std*. In some cases allowing the removal ofio andcontextlib imports.

• test_ast/test_ast.py -L3304,L3348
• test_compile.py -L971
• test_compileall.py -L92,L102,L209
• test_concurrent_futures/test_interpreter_pool.py -L201,L208,L221,L232,L246
• test_dis.py -L975,L992,L1713,L2432,L2459,L2510,L2544
• test_httpservers.py -L1321
• test_pdb.py -L4574
• test_pickle.py -L732,L760
• test_platform.py -L761,L769,L809
• test_profile.py -L96
• test_pyrepl/test_interact.py -L35,L52,L65,L75,L91,L100,L110,L138,L150,L163,L171
• test_regrtest.py -L369
• test_remote_pdb.py -L1526
• test_sqlite3/util.py -L50
• test_tokenize.py -L3185,L3212
• test_uuid.py -L1149,L1182,L1195,L1210,L1224

Instances oftest.support.captured_output("std*") swappable for a correspondingtest.support.captured_std*. Low risk to change since the latter calls the former.

• test_descr.py -L1298
• test_future_stmt/test_future_multiple_features.py -L15
• test_itertools.py -L882
• test_sys.py -L198,L1487
• test_threading.py -L2058,L2074,L2097,L2137,L2148
• test_traceback.py -L600,L1817,L1821,L1858,L1871,L1892,L1943,L1983,L2013,L2045,L2117,L2138,L2149,L2159,L3016,L3032,L4817
• test_warnings/__init__.py -L900,L914,L927,L942

Tests with a manual stream save/restore (most are stdin). Higher risk especially when replacing over long blocks.

• libregrtest/single.py -L297
• test_builtin.py -L1748
• test_capi/check_config.py -L70
• test_concurrent_futures/test_deadlock.py -L148
• test_exceptions.py -L71
• test_faulthandler.py -L399,L806
• test_fileinput.py -L129,L151
• test_optparse.py -L160
• test_profile.py -L90 &L101 callsilent which could betest.support.captured_stdout instead of reimplementing the function.
• test_pydoc.py -L478
• test_unittest/test_runner.py -L1425
• test_winconsoleio.py -L170
• test_wsgiref.py -L74

Linked PRs

• gh-136632: use support.captured_std* in test_pyrepl/test_interact.py #136633