bpo-33053: -m now adds *starting* directory to sys.path (GH-6231)

Historically, -m added the empty string as sys.path
zero, meaning it resolved imports against the current
working directory, the same way -c and the interactive
prompt do.

This changes the sys.path initialisation to add the
*starting* working directory as sys.path[0] instead,
such that changes to the working directory while the
program is running will have no effect on imports
when using the -m switch.

1 files changed, 11 insertions, 5 deletions

diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index f0eb528..83941c1 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -9,7 +9,7 @@ import os
 import sys
 import importlib
 import unittest
-
+import tempfile
 
 # NOTE: There are some additional tests relating to interaction with
 #       zipimport in the test_zipimport_support test module.
@@ -688,10 +688,16 @@ class TestDocTestFinder(unittest.TestCase):
 
     def test_empty_namespace_package(self):
         pkg_name = 'doctest_empty_pkg'
-        os.mkdir(pkg_name)
-        mod = importlib.import_module(pkg_name)
-        assert doctest.DocTestFinder().find(mod) == []
-        os.rmdir(pkg_name)
+        with tempfile.TemporaryDirectory() as parent_dir:
+            pkg_dir = os.path.join(parent_dir, pkg_name)
+            os.mkdir(pkg_dir)
+            sys.path.append(parent_dir)
+            try:
+                mod = importlib.import_module(pkg_name)
+            finally:
+                support.forget(pkg_name)
+                sys.path.pop()
+            assert doctest.DocTestFinder().find(mod) == []
 
 
 def test_DocTestParser(): r"""