Issue #19776: Add a expanduser() method on Path objects.

Patch by Serhiy.

Doc/library/pathlib.rst

@@ -670,6 +670,18 @@ call fails (for example because the path doesn't exist):
       symlink *points to* an existing file or directory.
 
 
+.. method:: Path.expanduser()
+
+   Return a new path with expanded ``~`` and ``~user`` constructs,
+   as returned by :meth:`os.path.expanduser`::
+
+      >>> p = PosixPath('~/films/Monty Python')
+      >>> p.expanduser()
+      PosixPath('/home/eric/films/Monty Python')
+
+   .. versionadded:: 3.5
+
+
 .. method:: Path.glob(pattern)
 
    Glob the given *pattern* in the directory represented by this path,
@@ -1003,7 +1015,4 @@ call fails (for example because the path doesn't exist):
       >>> p.read_text()
       'Text file contents'
 
-   An existing file of the same name is overwritten.  The optional parameters
-   have the same meaning as in :func:`open`.
-
    .. versionadded:: 3.5

Lib/pathlib.py

@@ -221,6 +221,36 @@ class _WindowsFlavour(_Flavour):
             # It's a path on a network drive => 'file://host/share/a/b'
             return 'file:' + urlquote_from_bytes(path.as_posix().encode('utf-8'))
 
+    def gethomedir(self, username):
+        if 'HOME' in os.environ:
+            userhome = os.environ['HOME']
+        elif 'USERPROFILE' in os.environ:
+            userhome = os.environ['USERPROFILE']
+        elif 'HOMEPATH' in os.environ:
+                try:
+                    drv = os.environ['HOMEDRIVE']
+                except KeyError:
+                    drv = ''
+                userhome = drv + os.environ['HOMEPATH']
+        else:
+            raise RuntimeError("Can't determine home directory")
+
+        if username:
+            # Try to guess user home directory.  By default all users
+            # directories are located in the same place and are named by
+            # corresponding usernames.  If current user home directory points
+            # to nonstandard place, this guess is likely wrong.
+            if os.environ['USERNAME'] != username:
+                drv, root, parts = self.parse_parts((userhome,))
+                if parts[-1] != os.environ['USERNAME']:
+                    raise RuntimeError("Can't determine home directory "
+                                       "for %r" % username)
+                parts[-1] = username
+                if drv or root:
+                    userhome = drv + root + self.join(parts[1:])
+                else:
+                    userhome = self.join(parts)
+        return userhome
 
 class _PosixFlavour(_Flavour):
     sep = '/'
@@ -304,6 +334,21 @@ class _PosixFlavour(_Flavour):
         bpath = bytes(path)
         return 'file://' + urlquote_from_bytes(bpath)
 
+    def gethomedir(self, username):
+        if not username:
+            try:
+                return os.environ['HOME']
+            except KeyError:
+                import pwd
+                return pwd.getpwuid(os.getuid()).pw_dir
+        else:
+            import pwd
+            try:
+                return pwd.getpwnam(username).pw_dir
+            except KeyError:
+                raise RuntimeError("Can't determine home directory "
+                                   "for %r" % username)
+
 
 _windows_flavour = _WindowsFlavour()
 _posix_flavour = _PosixFlavour()
@@ -1333,6 +1378,17 @@ class Path(PurePath):
             # (see https://bitbucket.org/pitrou/pathlib/issue/12/)
             return False
 
+    def expanduser(self):
+        """ Return a new path with expanded ~ and ~user constructs
+        (as returned by os.path.expanduser)
+        """
+        if (not (self._drv or self._root) and
+            self._parts and self._parts[0][:1] == '~'):
+            homedir = self._flavour.gethomedir(self._parts[0][1:])
+            return self._from_parts([homedir] + self._parts[1:])
+
+        return self
+
 
 class PosixPath(Path, PurePosixPath):
     __slots__ = ()

Lib/test/test_pathlib.py

@@ -1286,6 +1286,19 @@ class _BasePathTest(object):
         p = self.cls('')
         self.assertEqual(p.stat(), os.stat('.'))
 
+    def test_expanduser_common(self):
+        P = self.cls
+        p = P('~')
+        self.assertEqual(p.expanduser(), P(os.path.expanduser('~')))
+        p = P('foo')
+        self.assertEqual(p.expanduser(), p)
+        p = P('/~')
+        self.assertEqual(p.expanduser(), p)
+        p = P('../~')
+        self.assertEqual(p.expanduser(), p)
+        p = P(P('').absolute().anchor) / '~'
+        self.assertEqual(p.expanduser(), p)
+
     def test_exists(self):
         P = self.cls
         p = P(BASE)
@@ -1959,6 +1972,48 @@ class PosixPathTest(_BasePathTest, unittest.TestCase):
         self.assertEqual(given, expect)
         self.assertEqual(set(p.rglob("FILEd*")), set())
 
+    def test_expanduser(self):
+        P = self.cls
+        support.import_module('pwd')
+        import pwd
+        pwdent = pwd.getpwuid(os.getuid())
+        username = pwdent.pw_name
+        userhome = pwdent.pw_dir.rstrip('/')
+        # find arbitrary different user (if exists)
+        for pwdent in pwd.getpwall():
+            othername = pwdent.pw_name
+            otherhome = pwdent.pw_dir.rstrip('/')
+            if othername != username:
+                break
+
+        p1 = P('~/Documents')
+        p2 = P('~' + username + '/Documents')
+        p3 = P('~' + othername + '/Documents')
+        p4 = P('../~' + username + '/Documents')
+        p5 = P('/~' + username + '/Documents')
+        p6 = P('')
+        p7 = P('~fakeuser/Documents')
+
+        with support.EnvironmentVarGuard() as env:
+            env.pop('HOME', None)
+
+            self.assertEqual(p1.expanduser(), P(userhome) / 'Documents')
+            self.assertEqual(p2.expanduser(), P(userhome) / 'Documents')
+            self.assertEqual(p3.expanduser(), P(otherhome) / 'Documents')
+            self.assertEqual(p4.expanduser(), p4)
+            self.assertEqual(p5.expanduser(), p5)
+            self.assertEqual(p6.expanduser(), p6)
+            self.assertRaises(RuntimeError, p7.expanduser)
+
+            env['HOME'] = '/tmp'
+            self.assertEqual(p1.expanduser(), P('/tmp/Documents'))
+            self.assertEqual(p2.expanduser(), P(userhome) / 'Documents')
+            self.assertEqual(p3.expanduser(), P(otherhome) / 'Documents')
+            self.assertEqual(p4.expanduser(), p4)
+            self.assertEqual(p5.expanduser(), p5)
+            self.assertEqual(p6.expanduser(), p6)
+            self.assertRaises(RuntimeError, p7.expanduser)
+
 
 @only_nt
 class WindowsPathTest(_BasePathTest, unittest.TestCase):
@@ -1974,6 +2029,61 @@ class WindowsPathTest(_BasePathTest, unittest.TestCase):
         p = P(BASE, "dirC")
         self.assertEqual(set(p.rglob("FILEd")), { P(BASE, "dirC/dirD/fileD") })
 
+    def test_expanduser(self):
+        P = self.cls
+        with support.EnvironmentVarGuard() as env:
+            env.pop('HOME', None)
+            env.pop('USERPROFILE', None)
+            env.pop('HOMEPATH', None)
+            env.pop('HOMEDRIVE', None)
+            env['USERNAME'] = 'alice'
+
+            # test that the path returns unchanged
+            p1 = P('~/My Documents')
+            p2 = P('~alice/My Documents')
+            p3 = P('~bob/My Documents')
+            p4 = P('/~/My Documents')
+            p5 = P('d:~/My Documents')
+            p6 = P('')
+            self.assertRaises(RuntimeError, p1.expanduser)
+            self.assertRaises(RuntimeError, p2.expanduser)
+            self.assertRaises(RuntimeError, p3.expanduser)
+            self.assertEqual(p4.expanduser(), p4)
+            self.assertEqual(p5.expanduser(), p5)
+            self.assertEqual(p6.expanduser(), p6)
+
+            def check():
+                env.pop('USERNAME', None)
+                self.assertEqual(p1.expanduser(),
+                                 P('C:/Users/alice/My Documents'))
+                self.assertRaises(KeyError, p2.expanduser)
+                env['USERNAME'] = 'alice'
+                self.assertEqual(p2.expanduser(),
+                                 P('C:/Users/alice/My Documents'))
+                self.assertEqual(p3.expanduser(),
+                                 P('C:/Users/bob/My Documents'))
+                self.assertEqual(p4.expanduser(), p4)
+                self.assertEqual(p5.expanduser(), p5)
+                self.assertEqual(p6.expanduser(), p6)
+
+            # test the first lookup key in the env vars
+            env['HOME'] = 'C:\\Users\\alice'
+            check()
+
+            # test that HOMEPATH is available instead
+            env.pop('HOME', None)
+            env['HOMEPATH'] = 'C:\\Users\\alice'
+            check()
+
+            env['HOMEDRIVE'] = 'C:\\'
+            env['HOMEPATH'] = 'Users\\alice'
+            check()
+
+            env.pop('HOMEDRIVE', None)
+            env.pop('HOMEPATH', None)
+            env['USERPROFILE'] = 'C:\\Users\\alice'
+            check()
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS

@@ -196,6 +196,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #19776: Add a expanduser() method on Path objects.
+
 - Issue #23112: Fix SimpleHTTPServer to correctly carry the query string and
   fragment when it redirects to add a trailing slash.