bpo-41718: Reduce test.libregrtest imports

Lib/test/libregrtest/save_env.py

@@ -1,4 +1,3 @@
-import asyncio
 import builtins
 import locale
 import logging
@@ -7,15 +6,10 @@
 import sys
 import sysconfig
 import threading
-import urllib.request
 import warnings
 from test import support
 from test.support import os_helper
 from test.libregrtest.utils import print_warning
-try:
-    import _multiprocessing, multiprocessing.process
-except ImportError:
-    multiprocessing = None
 
 
 # Unit tests are supposed to leave the execution environment unchanged
@@ -63,32 +57,12 @@ def __init__(self, testname, verbose=0, quiet=False, *, pgo=False):
                  'warnings.filters', 'asyncore.socket_map',
                  'logging._handlers', 'logging._handlerList', 'sys.gettrace',
                  'sys.warnoptions',
-                 # multiprocessing.process._cleanup() may release ref
-                 # to a thread, so check processes first.
-                 'multiprocessing.process._dangling', 'threading._dangling',
+                 'threading._dangling',
                  'sysconfig._CONFIG_VARS', 'sysconfig._INSTALL_SCHEMES',
                  'files', 'locale', 'warnings.showwarning',
                  'shutil_archive_formats', 'shutil_unpack_formats',
-                 'asyncio.events._event_loop_policy',
-                 'urllib.requests._url_tempfiles', 'urllib.requests._opener',
                 )
 
-    def get_urllib_requests__url_tempfiles(self):
-        return list(urllib.request._url_tempfiles)
-    def restore_urllib_requests__url_tempfiles(self, tempfiles):
-        for filename in tempfiles:
-            os_helper.unlink(filename)
-
-    def get_urllib_requests__opener(self):
-        return urllib.request._opener
-    def restore_urllib_requests__opener(self, opener):
-        urllib.request._opener = opener
-
-    def get_asyncio_events__event_loop_policy(self):
-        return support.maybe_get_event_loop_policy()
-    def restore_asyncio_events__event_loop_policy(self, policy):
-        asyncio.set_event_loop_policy(policy)
-
     def get_sys_argv(self):
         return id(sys.argv), sys.argv, sys.argv[:]
     def restore_sys_argv(self, saved_argv):
@@ -206,20 +180,6 @@ def restore_threading__dangling(self, saved):
         threading._dangling.clear()
         threading._dangling.update(saved)
 
-    # Same for Process objects
-    def get_multiprocessing_process__dangling(self):
-        if not multiprocessing:
-            return None
-        # Unjoined process objects can survive after process exits
-        multiprocessing.process._cleanup()
-        # This copies the weakrefs without making any strong reference
-        return multiprocessing.process._dangling.copy()
-    def restore_multiprocessing_process__dangling(self, saved):
-        if not multiprocessing:
-            return
-        multiprocessing.process._dangling.clear()
-        multiprocessing.process._dangling.update(saved)
-
     def get_sysconfig__CONFIG_VARS(self):
         # make sure the dict is initialized
         sysconfig.get_config_var('prefix')

Lib/test/test_regrtest.py

@@ -520,7 +520,7 @@ def run_command(self, args, input=None, exitcode=0, **kw):
         if 'stderr' not in kw:
             kw['stderr'] = subprocess.STDOUT
         proc = subprocess.run(args,
-                              universal_newlines=True,
+                              text=True,
                               input=input,
                               stdout=subprocess.PIPE,
                               **kw)
@@ -1307,5 +1307,21 @@ def test_format_duration(self):
                          '3 hour 1 sec')
 
 
+class MiscTestCase(BaseTestCase):
+    def test_num_imports(self):
+        # bpo-41718: "import test.libregrtest" must not import too many
+        # modules.
+        code = textwrap.dedent("""
+            import sys
+            import test.libregrtest
+            print(len(sys.modules))
+        """)
+        proc = self.run_command([sys.executable, '-I', '-c', code])
+        out = proc.stdout.strip()
+        nmodules = int(out)
+        # Python 3.10 on Linux imports 149 modules
+        self.assertLess(nmodules, 155)
+
+
 if __name__ == '__main__':
     unittest.main()

Lib/test/test_support.py

@@ -468,7 +468,7 @@ def check_options(self, args, func, expected=None):
         proc = subprocess.run(cmd,
                               stdout=subprocess.PIPE,
                               stderr=subprocess.DEVNULL,
-                              universal_newlines=True,
+                              text=True,
                               env=env)
         if expected is None:
             expected = args
@@ -656,6 +656,20 @@ def test_print_warning(self):
         self.check_print_warning("a\nb",
                                  'Warning -- a\nWarning -- b\n')
 
+    def test_num_imports(self):
+        # bpo-41718: "import test.support" must not import too many modules.
+        code = textwrap.dedent("""
+            import sys
+            import test.support
+            print(len(sys.modules))
+        """)
+        cmd = [sys.executable, '-I', '-c', code]
+        proc = subprocess.run(cmd, stdout=subprocess.PIPE, text=True, check=True)
+        out = proc.stdout.strip()
+        nmodules = int(out)
+        # Python 3.10 on Linux imports 96 modules
+        self.assertLess(nmodules, 100)
+
     # XXX -follows a list of untested API
     # make_legacy_pyc
     # is_resource_enabled

Misc/NEWS.d/next/Tests/2020-09-04-17-50-28.bpo-41718.MBxAOC.rst

@@ -0,0 +1,2 @@
+test.libregrtest.save_env no longer imports asyncio, multiprocessing nor
+urllib to reduce the number of imports, to better isolate unit tests.