From 333545df96e4786761f6b5c14e23990532179413 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Thu, 9 Nov 2023 15:08:12 +0100
Subject: [PATCH] gh-111881: Use lazy import in unittest

Use lazy imports for argparse, difflib and fnmatch imports in
unittest to speedup Python startup time when running tests, and the
number of imported modules when running tests.
---
 Lib/unittest/case.py   |  5 ++++-
 Lib/unittest/loader.py | 11 +++++++----
 Lib/unittest/main.py   |  6 ++++--
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index 811557498bb30e..3d8eb41d946f2e 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -2,7 +2,6 @@
 
 import sys
 import functools
-import difflib
 import pprint
 import re
 import warnings
@@ -1065,6 +1064,8 @@ def assertSequenceEqual(self, seq1, seq2, msg=None, seq_type=None):
                 except (TypeError, IndexError, NotImplementedError):
                     differing += ('Unable to index element %d '
                                   'of second %s\n' % (len1, seq_type_name))
+
+        import difflib
         standardMsg = differing
         diffMsg = '\n' + '\n'.join(
             difflib.ndiff(pprint.pformat(seq1).splitlines(),
@@ -1178,6 +1179,7 @@ def assertDictEqual(self, d1, d2, msg=None):
         self.assertIsInstance(d2, dict, 'Second argument is not a dictionary')
 
         if d1 != d2:
+            import difflib
             standardMsg = '%s != %s' % _common_shorten_repr(d1, d2)
             diff = ('\n' + '\n'.join(difflib.ndiff(
                            pprint.pformat(d1).splitlines(),
@@ -1247,6 +1249,7 @@ def assertMultiLineEqual(self, first, second, msg=None):
             secondlines = second_presplit.splitlines(keepends=True)
 
             # Generate the message and diff, then raise the exception
+            import difflib
             standardMsg = '%s != %s' % _common_shorten_repr(first, second)
             diff = '\n' + ''.join(difflib.ndiff(firstlines, secondlines))
             standardMsg = self._truncateMessage(standardMsg, diff)
diff --git a/Lib/unittest/loader.py b/Lib/unittest/loader.py
index 9a3e5cc4bf30e5..cf6543e19ac8d4 100644
--- a/Lib/unittest/loader.py
+++ b/Lib/unittest/loader.py
@@ -7,8 +7,6 @@
 import types
 import functools
 
-from fnmatch import fnmatch, fnmatchcase
-
 from . import case, suite, util
 
 __unittest = True
@@ -219,8 +217,12 @@ def shouldIncludeMethod(attrname):
             fullName = f'%s.%s.%s' % (
                 testCaseClass.__module__, testCaseClass.__qualname__, attrname
             )
-            return self.testNamePatterns is None or \
-                any(fnmatchcase(fullName, pattern) for pattern in self.testNamePatterns)
+            if self.testNamePatterns is None:
+                return True
+            else:
+                from fnmatch import fnmatchcase
+                return any(fnmatchcase(fullName, pattern) for pattern in self.testNamePatterns)
+
         testFnNames = list(filter(shouldIncludeMethod, dir(testCaseClass)))
         if self.sortTestMethodsUsing:
             testFnNames.sort(key=functools.cmp_to_key(self.sortTestMethodsUsing))
@@ -339,6 +341,7 @@ def _get_module_from_name(self, name):
 
     def _match_path(self, path, full_path, pattern):
         # override this method to use alternative matching strategy
+        from fnmatch import fnmatch
         return fnmatch(path, pattern)
 
     def _find_tests(self, start_dir, pattern):
diff --git a/Lib/unittest/main.py b/Lib/unittest/main.py
index d29a9f91fcca42..787f46e902022e 100644
--- a/Lib/unittest/main.py
+++ b/Lib/unittest/main.py
@@ -1,8 +1,7 @@
 """Unittest main program"""
 
-import sys
-import argparse
 import os
+import sys
 
 from . import loader, runner
 from .signals import installHandler
@@ -159,6 +158,7 @@ def _initArgParsers(self):
         self._discovery_parser = self._getDiscoveryArgParser(parent_parser)
 
     def _getParentArgParser(self):
+        import argparse
         parser = argparse.ArgumentParser(add_help=False)
 
         parser.add_argument('-v', '--verbose', dest='verbosity',
@@ -197,6 +197,7 @@ def _getParentArgParser(self):
         return parser
 
     def _getMainArgParser(self, parent):
+        import argparse
         parser = argparse.ArgumentParser(parents=[parent])
         parser.prog = self.progName
         parser.print_help = self._print_help
@@ -208,6 +209,7 @@ def _getMainArgParser(self, parent):
         return parser
 
     def _getDiscoveryArgParser(self, parent):
+        import argparse
         parser = argparse.ArgumentParser(parents=[parent])
         parser.prog = '%s discover' % self.progName
         parser.epilog = ('For test discovery all test modules must be '