python · miss-islington · Apr 15, 2018 · Apr 15, 2018
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
@@ -1151,9 +1151,10 @@ Changes in Python behavior
   (Contributed by Serhiy Storchaka in :issue:`32012` and :issue:`32023`.)
 
 * When using the ``-m`` switch, the starting directory is now added to sys.path,
-  rather than the current working directory. Any programs that are found to be
-  relying on the previous behaviour will need to be updated to manipulate
-  :data:`sys.path` appropriately.
+  rather than the current working directory. Any programs that are checking for
+  the empty string in :data:`sys.path`, or otherwise relying on the previous
+  behaviour, will need to be updated accordingly (e.g. by checking for
+  ``os.getcwd()`` in addition to checking for the empty string).
 
 
 Changes in the Python API

diff --git a/Lib/pydoc.py b/Lib/pydoc.py
@@ -2614,18 +2614,50 @@ def browse(port=0, *, open_browser=True, hostname='localhost'):
 def ispath(x):
     return isinstance(x, str) and x.find(os.sep) >= 0
 
+def _get_revised_path(given_path, argv0):
+    """Ensures current directory is on returned path, and argv0 directory is not
+
+    Exception: argv0 dir is left alone if it's also pydoc's directory.
+
+    Returns a new path entry list, or None if no adjustment is needed.
+    """
+    # Scripts may get the current directory in their path by default if they're
+    # run with the -m switch, or directly from the current directory.
+    # The interactive prompt also allows imports from the current directory.
+
+    # Accordingly, if the current directory is already present, don't make
+    # any changes to the given_path
+    if '' in given_path or os.curdir in given_path or os.getcwd() in given_path:
+        return None
+
+    # Otherwise, add the current directory to the given path, and remove the
+    # script directory (as long as the latter isn't also pydoc's directory.
+    stdlib_dir = os.path.dirname(__file__)
+    script_dir = os.path.dirname(argv0)
+    revised_path = given_path.copy()
+    if script_dir in given_path and not os.path.samefile(script_dir, stdlib_dir):
+        revised_path.remove(script_dir)
+    revised_path.insert(0, os.getcwd())
+    return revised_path
+
+
+# Note: the tests only cover _get_revised_path, not _adjust_cli_path itself
+def _adjust_cli_sys_path():
+    """Ensures current directory is on sys.path, and __main__ directory is not
+
+    Exception: __main__ dir is left alone if it's also pydoc's directory.
+    """
+    revised_path = _get_revised_path(sys.path, sys.argv[0])
+    if revised_path is not None:
+        sys.path[:] = revised_path
+
+
 def cli():
     """Command-line interface (looks at sys.argv to decide what to do)."""
     import getopt
     class BadUsage(Exception): pass
 
-    # Scripts don't get the current directory in their path by default
-    # unless they are run with the '-m' switch
-    if '' not in sys.path:
-        scriptdir = os.path.dirname(sys.argv[0])
-        if scriptdir in sys.path:
-            sys.path.remove(scriptdir)
-        sys.path.insert(0, '.')
+    _adjust_cli_sys_path()
 
     try:
         opts, args = getopt.getopt(sys.argv[1:], 'bk:n:p:w')

diff --git a/Lib/test/test_pydoc.py b/Lib/test/test_pydoc.py
@@ -11,6 +11,7 @@
 import re
 import stat
 import string
+import tempfile
 import test.support
 import time
 import types
@@ -1084,6 +1085,71 @@ def test_resolve_false(self):
         self.assertIn('class Enum', helptext)
 
 
+class TestInternalUtilities(unittest.TestCase):
+
+    def setUp(self):
+        tmpdir = tempfile.TemporaryDirectory()
+        self.argv0dir = tmpdir.name
+        self.argv0 = os.path.join(tmpdir.name, "nonexistent")
+        self.addCleanup(tmpdir.cleanup)
+        self.abs_curdir = abs_curdir = os.getcwd()
+        self.curdir_spellings = ["", os.curdir, abs_curdir]
+
+    def _get_revised_path(self, given_path, argv0=None):
+        # Checking that pydoc.cli() actually calls pydoc._get_revised_path()
+        # is handled via code review (at least for now).
+        if argv0 is None:
+            argv0 = self.argv0
+        return pydoc._get_revised_path(given_path, argv0)
+
+    def _get_starting_path(self):
+        # Get a copy of sys.path without the current directory
+        clean_path = sys.path.copy()
+        for spelling in self.curdir_spellings:
+            for __ in range(clean_path.count(spelling)):
+                clean_path.remove(spelling)
+        return clean_path
+
+    def test_sys_path_adjustment_adds_missing_curdir(self):
+        clean_path = self._get_starting_path()
+        expected_path = [self.abs_curdir] + clean_path
+        self.assertEqual(self._get_revised_path(clean_path), expected_path)
+
+    def test_sys_path_adjustment_removes_argv0_dir(self):
+        clean_path = self._get_starting_path()
+        expected_path = [self.abs_curdir] + clean_path
+        leading_argv0dir = [self.argv0dir] + clean_path
+        self.assertEqual(self._get_revised_path(leading_argv0dir), expected_path)
+        trailing_argv0dir = clean_path + [self.argv0dir]
+        self.assertEqual(self._get_revised_path(trailing_argv0dir), expected_path)
+
+
+    def test_sys_path_adjustment_protects_pydoc_dir(self):
+        def _get_revised_path(given_path):
+            return self._get_revised_path(given_path, argv0=pydoc.__file__)
+        clean_path = self._get_starting_path()
+        leading_argv0dir = [self.argv0dir] + clean_path
+        expected_path = [self.abs_curdir] + leading_argv0dir
+        self.assertEqual(_get_revised_path(leading_argv0dir), expected_path)
+        trailing_argv0dir = clean_path + [self.argv0dir]
+        expected_path = [self.abs_curdir] + trailing_argv0dir
+        self.assertEqual(_get_revised_path(trailing_argv0dir), expected_path)
+
+    def test_sys_path_adjustment_when_curdir_already_included(self):
+        clean_path = self._get_starting_path()
+        for spelling in self.curdir_spellings:
+            with self.subTest(curdir_spelling=spelling):
+                # If curdir is already present, no alterations are made at all
+                leading_curdir = [spelling] + clean_path
+                self.assertIsNone(self._get_revised_path(leading_curdir))
+                trailing_curdir = clean_path + [spelling]
+                self.assertIsNone(self._get_revised_path(trailing_curdir))
+                leading_argv0dir = [self.argv0dir] + leading_curdir
+                self.assertIsNone(self._get_revised_path(leading_argv0dir))
+                trailing_argv0dir = trailing_curdir + [self.argv0dir]
+                self.assertIsNone(self._get_revised_path(trailing_argv0dir))
+
+
 @reap_threads
 def test_main():
     try:
@@ -1094,6 +1160,7 @@ def test_main():
                                   PydocUrlHandlerTest,
                                   TestHelper,
                                   PydocWithMetaClasses,
+                                  TestInternalUtilities,
                                   )
     finally:
         reap_children()

diff --git a/Misc/NEWS.d/next/Library/2018-04-08-22-54-07.bpo-33185.Id-Ba9.rst b/Misc/NEWS.d/next/Library/2018-04-08-22-54-07.bpo-33185.Id-Ba9.rst
@@ -0,0 +1,5 @@
+Fixed regression when running pydoc with the ``-m`` switch. (The regression
+was introduced in 3.7.0b3 by the resolution of bpo-33053)
+
+This fix also changed pydoc to add ``os.getcwd()`` to ``sys.path`` when
+necessary, rather than adding ``"."``.