pathlib ABCs: Require one or more initialiser arguments (python#113885)

Refuse to guess what a user means when they initialise a pathlib ABC
without any positional arguments. In mainline pathlib it's normalised to
`.`, but in the ABCs this guess isn't appropriate; for example, the path
type may not represent the current directory as `.`, or may have no concept
of a "current directory" at all.

Lib/pathlib/_abc.py

@@ -167,13 +167,7 @@ def with_segments(self, *pathsegments):
  def __str__(self):
  """Return the string representation of the path, suitable for
  passing to system calls."""
- paths = self._raw_paths
- if len(paths) == 1:
- return paths[0]
- elif paths:
- return self.pathmod.join(*paths)
- else:
- return ''
+ return self.pathmod.join(*self._raw_paths)
 
  def as_posix(self):
  """Return the string representation of the path with forward (/)
@@ -838,7 +832,7 @@ def cwd(cls):
  # enable users to replace the implementation of 'absolute()' in a
  # subclass and benefit from the new behaviour here. This works because
  # os.path.abspath('.') == os.getcwd().
- return cls().absolute()
+ return cls('').absolute()
 
  def expanduser(self):
  """ Return a new path with expanded ~ and ~user constructs

Lib/test/test_pathlib/test_pathlib_abc.py

@@ -227,9 +227,9 @@ def test_match_common(self):
  self.assertFalse(P('c:/a/B.Py').match('C:/A/*.pY', case_sensitive=True))
  self.assertTrue(P('/a/b/c.py').match('/A/*/*.Py', case_sensitive=False))
  # Matching against empty path
- self.assertFalse(P().match('*'))
- self.assertTrue(P().match('**'))
- self.assertFalse(P().match('**/*'))
+ self.assertFalse(P('').match('*'))
+ self.assertTrue(P('').match('**'))
+ self.assertFalse(P('').match('**/*'))
 
  def test_parts_common(self):
  # `parts` returns a tuple.
@@ -249,8 +249,8 @@ def test_parent_common(self):
  p = P('a/b/c')
  self.assertEqual(p.parent, P('a/b'))
  self.assertEqual(p.parent.parent, P('a'))
- self.assertEqual(p.parent.parent.parent, P())
- self.assertEqual(p.parent.parent.parent.parent, P())
+ self.assertEqual(p.parent.parent.parent, P(''))
+ self.assertEqual(p.parent.parent.parent.parent, P(''))
  # Anchored
  p = P('/a/b/c')
  self.assertEqual(p.parent, P('/a/b'))
@@ -478,20 +478,20 @@ def test_relative_to_common(self):
  p = P('a/b')
  self.assertRaises(TypeError, p.relative_to)
  self.assertRaises(TypeError, p.relative_to, b'a')
- self.assertEqual(p.relative_to(P()), P('a/b'))
+ self.assertEqual(p.relative_to(P('')), P('a/b'))
  self.assertEqual(p.relative_to(''), P('a/b'))
  self.assertEqual(p.relative_to(P('a')), P('b'))
  self.assertEqual(p.relative_to('a'), P('b'))
  self.assertEqual(p.relative_to('a/'), P('b'))
- self.assertEqual(p.relative_to(P('a/b')), P())
- self.assertEqual(p.relative_to('a/b'), P())
- self.assertEqual(p.relative_to(P(), walk_up=True), P('a/b'))
+ self.assertEqual(p.relative_to(P('a/b')), P(''))
+ self.assertEqual(p.relative_to('a/b'), P(''))
+ self.assertEqual(p.relative_to(P(''), walk_up=True), P('a/b'))
  self.assertEqual(p.relative_to('', walk_up=True), P('a/b'))
  self.assertEqual(p.relative_to(P('a'), walk_up=True), P('b'))
  self.assertEqual(p.relative_to('a', walk_up=True), P('b'))
  self.assertEqual(p.relative_to('a/', walk_up=True), P('b'))
- self.assertEqual(p.relative_to(P('a/b'), walk_up=True), P())
- self.assertEqual(p.relative_to('a/b', walk_up=True), P())
+ self.assertEqual(p.relative_to(P('a/b'), walk_up=True), P(''))
+ self.assertEqual(p.relative_to('a/b', walk_up=True), P(''))
  self.assertEqual(p.relative_to(P('a/c'), walk_up=True), P('../b'))
  self.assertEqual(p.relative_to('a/c', walk_up=True), P('../b'))
  self.assertEqual(p.relative_to(P('a/b/c'), walk_up=True), P('..'))
@@ -517,15 +517,15 @@ def test_relative_to_common(self):
  self.assertEqual(p.relative_to(P('/a')), P('b'))
  self.assertEqual(p.relative_to('/a'), P('b'))
  self.assertEqual(p.relative_to('/a/'), P('b'))
- self.assertEqual(p.relative_to(P('/a/b')), P())
- self.assertEqual(p.relative_to('/a/b'), P())
+ self.assertEqual(p.relative_to(P('/a/b')), P(''))
+ self.assertEqual(p.relative_to('/a/b'), P(''))
  self.assertEqual(p.relative_to(P('/'), walk_up=True), P('a/b'))
  self.assertEqual(p.relative_to('/', walk_up=True), P('a/b'))
  self.assertEqual(p.relative_to(P('/a'), walk_up=True), P('b'))
  self.assertEqual(p.relative_to('/a', walk_up=True), P('b'))
  self.assertEqual(p.relative_to('/a/', walk_up=True), P('b'))
- self.assertEqual(p.relative_to(P('/a/b'), walk_up=True), P())
- self.assertEqual(p.relative_to('/a/b', walk_up=True), P())
+ self.assertEqual(p.relative_to(P('/a/b'), walk_up=True), P(''))
+ self.assertEqual(p.relative_to('/a/b', walk_up=True), P(''))
  self.assertEqual(p.relative_to(P('/a/c'), walk_up=True), P('../b'))
  self.assertEqual(p.relative_to('/a/c', walk_up=True), P('../b'))
  self.assertEqual(p.relative_to(P('/a/b/c'), walk_up=True), P('..'))
@@ -536,7 +536,7 @@ def test_relative_to_common(self):
  self.assertRaises(ValueError, p.relative_to, P('/c'))
  self.assertRaises(ValueError, p.relative_to, P('/a/b/c'))
  self.assertRaises(ValueError, p.relative_to, P('/a/c'))
- self.assertRaises(ValueError, p.relative_to, P())
+ self.assertRaises(ValueError, p.relative_to, P(''))
  self.assertRaises(ValueError, p.relative_to, '')
  self.assertRaises(ValueError, p.relative_to, P('a'))
  self.assertRaises(ValueError, p.relative_to, P("../a"))
@@ -553,7 +553,7 @@ def test_is_relative_to_common(self):
  p = P('a/b')
  self.assertRaises(TypeError, p.is_relative_to)
  self.assertRaises(TypeError, p.is_relative_to, b'a')
- self.assertTrue(p.is_relative_to(P()))
+ self.assertTrue(p.is_relative_to(P('')))
  self.assertTrue(p.is_relative_to(''))
  self.assertTrue(p.is_relative_to(P('a')))
  self.assertTrue(p.is_relative_to('a/'))
@@ -576,7 +576,7 @@ def test_is_relative_to_common(self):
  self.assertFalse(p.is_relative_to(P('/c')))
  self.assertFalse(p.is_relative_to(P('/a/b/c')))
  self.assertFalse(p.is_relative_to(P('/a/c')))
- self.assertFalse(p.is_relative_to(P()))
+ self.assertFalse(p.is_relative_to(P('')))
  self.assertFalse(p.is_relative_to(''))
  self.assertFalse(p.is_relative_to(P('a')))
 
@@ -590,7 +590,7 @@ class PathBaseTest(PurePathBaseTest):
 
  def test_unsupported_operation(self):
  P = self.cls
- p = self.cls()
+ p = self.cls('')
  e = UnsupportedOperation
  self.assertRaises(e, p.stat)
  self.assertRaises(e, p.lstat)
@@ -634,13 +634,13 @@ def test_unsupported_operation(self):
 
  def test_as_uri_common(self):
  e = UnsupportedOperation
- self.assertRaises(e, self.cls().as_uri)
+ self.assertRaises(e, self.cls('').as_uri)
 
  def test_fspath_common(self):
- self.assertRaises(TypeError, os.fspath, self.cls())
+ self.assertRaises(TypeError, os.fspath, self.cls(''))
 
  def test_as_bytes_common(self):
- self.assertRaises(TypeError, bytes, self.cls())
+ self.assertRaises(TypeError, bytes, self.cls(''))
 
 
 class DummyPathIO(io.BytesIO):
@@ -993,7 +993,7 @@ def _check(glob, expected):
  _check(p.glob("*/"), ["dirA/", "dirB/", "dirC/", "dirE/", "linkB/"])
 
  def test_glob_empty_pattern(self):
- p = self.cls()
+ p = self.cls('')
  with self.assertRaisesRegex(ValueError, 'Unacceptable pattern'):
  list(p.glob(''))
 
@@ -1554,7 +1554,7 @@ def _check_complex_symlinks(self, link0_target):
 
  # Resolve relative paths.
  try:
- self.cls().absolute()
+ self.cls('').absolute()
  except UnsupportedOperation:
  return
  old_path = os.getcwd()