python
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
@@ -784,6 +784,11 @@ process and user.
    :func:`socket.gethostname`  or even
    ``socket.gethostbyaddr(socket.gethostname())``.
 
+   On macOS, iOS and Android, this returns the *kernel* name and version (i.e.,
+   ``'Darwin'`` on macOS and iOS; ``'Linux'`` on Android). :func:`platform.uname()`
+   can be used to get the user-facing operating system name and version on iOS and
+   Android.
+
    .. availability:: Unix.
 
    .. versionchanged:: 3.3

diff --git a/Doc/library/platform.rst b/Doc/library/platform.rst
@@ -148,6 +148,9 @@ Cross Platform
    Returns the system/OS name, such as ``'Linux'``, ``'Darwin'``, ``'Java'``,
    ``'Windows'``. An empty string is returned if the value cannot be determined.
 
+   On iOS and Android, this returns the user-facing OS name (i.e, ``'iOS``,
+   ``'iPadOS'`` or ``'Android'``). To obtain the kernel name (``'Darwin'`` or
+   ``'Linux'``), use :func:`os.uname()`.
 
 .. function:: system_alias(system, release, version)
 
@@ -161,6 +164,8 @@ Cross Platform
    Returns the system's release version, e.g. ``'#3 on degas'``. An empty string is
    returned if the value cannot be determined.
 
+   On iOS and Android, this is the user-facing OS version. To obtain the
+   Darwin or Linux kernel version, use :func:`os.uname()`.
 
 .. function:: uname()
 
@@ -238,7 +243,6 @@ Windows Platform
 macOS Platform
 --------------
 
-
 .. function:: mac_ver(release='', versioninfo=('','',''), machine='')
 
    Get macOS version information and return it as tuple ``(release, versioninfo,
@@ -248,6 +252,24 @@ macOS Platform
    Entries which cannot be determined are set to ``''``.  All tuple entries are
    strings.
 
+iOS Platform
+------------
+
+.. function:: ios_ver(system='', release='', model='', is_simulator=False)
+
+   Get iOS version information and return it as a
+   :func:`~collections.namedtuple` with the following attributes:
+
+   * ``system`` is the OS name; either ``'iOS'`` or ``'iPadOS'``.
+   * ``release`` is the iOS version number as a string (e.g., ``'17.2'``).
+   * ``model`` is the device model identifier; this will be a string like
+     ``'iPhone13,2'`` for a physical device, or ``'iPhone'`` on a simulator.
+   * ``is_simulator`` is a boolean describing if the app is running on a
+     simulator or a physical device.
+
+   Entries which cannot be determined are set to the defaults given as
+   parameters.
+
 
 Unix Platforms
 --------------

diff --git a/Doc/library/webbrowser.rst b/Doc/library/webbrowser.rst
@@ -33,6 +33,13 @@ allow the remote browser to maintain its own windows on the display.  If remote
 browsers are not available on Unix, the controlling process will launch a new
 browser and wait.
 
+On iOS, the :envvar:`BROWSER` environment variable, as well as any arguments
+controlling autoraise, browser preference, and new tab/window creation will be
+ignored. Web pages will *always* be opened in the user's preferred browser, in
+a new tab, with the browser being brought to the foreground. The use of the
+:mod:`webbrowser` module on iOS requires the :mod:`ctypes` module. If
+:mod:`ctypes` isn't available, calls to :func:`.open` will fail.
+
 The script :program:`webbrowser` can be used as a command-line interface for the
 module. It accepts a URL as the argument. It accepts the following optional
 parameters: ``-n`` opens the URL in a new browser window, if possible;
@@ -147,6 +154,8 @@ for the controller classes, all defined in this module.
 +------------------------+-----------------------------------------+-------+
 | ``'chromium-browser'`` | ``Chromium('chromium-browser')``        |       |
 +------------------------+-----------------------------------------+-------+
+| ``'iosbrowser'``       | ``IOSBrowser``                          | \(4)  |
++------------------------+-----------------------------------------+-------+
 
 Notes:
 
@@ -161,7 +170,10 @@ Notes:
    Only on Windows platforms.
 
 (3)
-   Only on macOS platform.
+   Only on macOS.
+
+(4)
+   Only on iOS.
 
 .. versionadded:: 3.2
    A new :class:`!MacOSXOSAScript` class has been added
@@ -176,6 +188,9 @@ Notes:
    Removed browsers include Grail, Mosaic, Netscape, Galeon,
    Skipstone, Iceape, and Firefox versions 35 and below.
 
+.. versionchanged:: 3.13
+   Support for iOS has been added.
+
 Here are some simple examples::
 
    url = 'https://docs.python.org/'

@@ -0,0 +1,71 @@
+import sys
+try:
+    from ctypes import cdll, c_void_p, c_char_p, util
+except ImportError:
+    # ctypes is an optional module. If it's not present, we're limited in what
+    # we can tell about the system, but we don't want to prevent the module
+    # from working.
+    print("ctypes isn't available; iOS system calls will not be available")
+    objc = None
+else:
+    # ctypes is available. Load the ObjC library, and wrap the objc_getClass,
+    # sel_registerName methods
+    lib = util.find_library("objc")
+    if lib is None:
+        # Failed to load the objc library
+        raise RuntimeError("ObjC runtime library couldn't be loaded")
+
+    objc = cdll.LoadLibrary(lib)
+    objc.objc_getClass.restype = c_void_p
+    objc.objc_getClass.argtypes = [c_char_p]
+    objc.sel_registerName.restype = c_void_p
+    objc.sel_registerName.argtypes = [c_char_p]
+
+
+def get_platform_ios():
+    # Determine if this is a simulator using the multiarch value
+    is_simulator = sys.implementation._multiarch.endswith("simulator")
-    is_simulator = sys.implementation._multiarch.endswith("simulator")
+    is_simulator = hasttr(sys.implementation, '_multiarch') and sys.implementation._multiarch.endswith("simulator")
-    is_simulator = sys.implementation._multiarch.endswith("simulator")
+    is_simulator = hasttr(sys.implementation, '_multiarch') and sys.implementation._multiarch.endswith("simulator")
+
+    # We can't use ctypes; abort
+    if not objc:
+        return None
+
+    # Most of the methods return ObjC objects
+    objc.objc_msgSend.restype = c_void_p
+    # All the methods used have no arguments.
+    objc.objc_msgSend.argtypes = [c_void_p, c_void_p]
+
+    # Equivalent of:
+    #   device = [UIDevice currentDevice]
+    UIDevice = objc.objc_getClass(b"UIDevice")
+    SEL_currentDevice = objc.sel_registerName(b"currentDevice")
+    device = objc.objc_msgSend(UIDevice, SEL_currentDevice)
+
+    # Equivalent of:
+    #   device_systemVersion = [device systemVersion]
+    SEL_systemVersion = objc.sel_registerName(b"systemVersion")
+    device_systemVersion = objc.objc_msgSend(device, SEL_systemVersion)
+
+    # Equivalent of:
+    #   device_systemName = [device systemName]
+    SEL_systemName = objc.sel_registerName(b"systemName")
+    device_systemName = objc.objc_msgSend(device, SEL_systemName)
+
+    # Equivalent of:
+    #   device_model = [device model]
+    SEL_model = objc.sel_registerName(b"model")
+    device_model = objc.objc_msgSend(device, SEL_model)
+
+    # UTF8String returns a const char*;
+    SEL_UTF8String = objc.sel_registerName(b"UTF8String")
+    objc.objc_msgSend.restype = c_char_p
+
+    # Equivalent of:
+    #   system = [device_systemName UTF8String]
+    #   release = [device_systemVersion UTF8String]
+    #   model = [device_model UTF8String]
+    system = objc.objc_msgSend(device_systemName, SEL_UTF8String).decode()
+    release = objc.objc_msgSend(device_systemVersion, SEL_UTF8String).decode()
+    model = objc.objc_msgSend(device_model, SEL_UTF8String).decode()
+
+    return system, release, model, is_simulator
diff --git a/Lib/platform.py b/Lib/platform.py
@@ -496,6 +496,30 @@ def mac_ver(release='', versioninfo=('', '', ''), machine=''):
     # If that also doesn't work return the default values
     return release, versioninfo, machine
 
+
+# A namedtuple for iOS version information.
+IOSVersionInfo = collections.namedtuple(
+    "IOSVersionInfo",
+    ["system", "release", "model", "is_simulator"]
+)
+
+
+def ios_ver(system="", release="", model="", is_simulator=False):
+    """Get iOS version information, and return it as a namedtuple:
+        (system, release, model, is_simulator).
+
+    If values can't be determined, they are set to values provided as
+    parameters.
+    """
+    if sys.platform == "ios":
+        import _ios_support
+        result = _ios_support.get_platform_ios()
+        if result is not None:
+            return IOSVersionInfo(*result)
+
+    return IOSVersionInfo(system, release, model, is_simulator)
+
+
 def _java_getprop(name, default):
     """This private helper is deprecated in 3.13 and will be removed in 3.15"""
     from java.lang import System
@@ -654,7 +678,7 @@ def _platform(*args):
         if cleaned == platform:
             break
         platform = cleaned
-    while platform[-1] == '-':
+    while platform and platform[-1] == '-':
         platform = platform[:-1]
 
     return platform
@@ -695,7 +719,7 @@ def _syscmd_file(target, default=''):
         default in case the command should fail.
 
     """
-    if sys.platform in ('dos', 'win32', 'win16'):
+    if sys.platform in {'dos', 'win32', 'win16', 'ios', 'tvos', 'watchos'}:
         # XXX Others too ?
         return default
 
@@ -859,6 +883,14 @@ def get_OpenVMS():
             csid, cpu_number = vms_lib.getsyi('SYI$_CPU', 0)
             return 'Alpha' if cpu_number >= 128 else 'VAX'
 
+    # On the iOS simulator, os.uname returns the architecture as uname.machine.
+    # On device it returns the model name for some reason; but there's only one
+    # CPU architecture for iOS devices, so we know the right answer.
+    def get_ios():
+        if sys.implementation._multiarch.endswith("simulator"):
+            return os.uname().machine
+        return 'arm64'
-        if sys.implementation._multiarch.endswith("simulator"):
-            return os.uname().machine
-        return 'arm64'
+        if hasattr(sys.implementation, '_multiarch') and sys.implementation._multiarch.endswith("simulator"):
+            return os.uname().machine
+        return 'arm64'
-        if sys.implementation._multiarch.endswith("simulator"):
-            return os.uname().machine
-        return 'arm64'
+        if hasattr(sys.implementation, '_multiarch') and sys.implementation._multiarch.endswith("simulator"):
+            return os.uname().machine
+        return 'arm64'
+
     def from_subprocess():
         """
         Fall back to `uname -p`
@@ -1018,6 +1050,10 @@ def uname():
         system = 'Android'
         release = android_ver().release
 
+    # Normalize responses on iOS
+    if sys.platform == 'ios':
+        system, release, _, _ = ios_ver()
+
     vals = system, node, release, version, machine
     # Replace 'unknown' values with the more portable ''
     _uname_cache = uname_result(*map(_unknown_as_blank, vals))
@@ -1297,11 +1333,14 @@ def platform(aliased=False, terse=False):
         system, release, version = system_alias(system, release, version)
 
     if system == 'Darwin':
-        # macOS (darwin kernel)
-        macos_release = mac_ver()[0]
-        if macos_release:
-            system = 'macOS'
-            release = macos_release
+        # macOS and iOS both report as a "Darwin" kernel
+        if sys.platform == "ios":
+            system, release, _, _ = ios_ver()
+        else:
+            macos_release = mac_ver()[0]
+            if macos_release:
+                system = 'macOS'
+                release = macos_release
 
     if system == 'Windows':
         # MS platforms

@@ -280,8 +280,8 @@ def _getuserbase():
     if env_base:
         return env_base
 
-    # Emscripten, VxWorks, and WASI have no home directories
-    if sys.platform in {"emscripten", "vxworks", "wasi"}:
+    # Emscripten, iOS, tvOS, VxWorks, WASI, and watchOS have no home directories
+    if sys.platform in {"emscripten", "ios", "tvos", "vxworks", "wasi", "watchos"}:
         return None
 
     def joinuser(*args):

@@ -21,6 +21,7 @@
 
 # Keys for get_config_var() that are never converted to Python integers.
 _ALWAYS_STR = {
+    'IPHONEOS_DEPLOYMENT_TARGET',
     'MACOSX_DEPLOYMENT_TARGET',
 }
 
@@ -57,6 +58,7 @@
         'scripts': '{base}/Scripts',
         'data': '{base}',
         },
+
     # Downstream distributors can overwrite the default install scheme.
     # This is done to support downstream modifications where distributors change
     # the installation layout (eg. different site-packages directory).
@@ -114,8 +116,8 @@ def _getuserbase():
     if env_base:
         return env_base
 
-    # Emscripten, VxWorks, and WASI have no home directories
-    if sys.platform in {"emscripten", "vxworks", "wasi"}:
+    # Emscripten, iOS, tvOS, VxWorks, WASI, and watchOS have no home directories
+    if sys.platform in {"emscripten", "ios", "tvos", "vxworks", "wasi", "watchos"}:
         return None
 
     def joinuser(*args):
@@ -290,6 +292,7 @@ def _get_preferred_schemes():
             'home': 'posix_home',
             'user': 'osx_framework_user',
         }
+
     return {
         'prefix': 'posix_prefix',
         'home': 'posix_home',
@@ -623,10 +626,15 @@ def get_platform():
         if m:
             release = m.group()
     elif osname[:6] == "darwin":
-        import _osx_support
-        osname, release, machine = _osx_support.get_platform_osx(
-                                            get_config_vars(),
-                                            osname, release, machine)
+        if sys.platform == "ios":
+            release = get_config_vars().get("IPHONEOS_DEPLOYMENT_TARGET", "12.0")
+            osname = sys.platform
+            machine = sys.implementation._multiarch
-            machine = sys.implementation._multiarch
+            machine = getattr(sys.implementation, '_multiarch', '')
-            machine = sys.implementation._multiarch
+            machine = getattr(sys.implementation, '_multiarch', '')
+        else:
+            import _osx_support
+            osname, release, machine = _osx_support.get_platform_osx(
+                                                get_config_vars(),
+                                                osname, release, machine)
 
     return f"{osname}-{release}-{machine}"
 

diff --git a/Lib/test/pythoninfo.py b/Lib/test/pythoninfo.py
@@ -290,6 +290,7 @@ def format_groups(groups):
         "HOMEDRIVE",
         "HOMEPATH",
         "IDLESTARTUP",
+        "IPHONEOS_DEPLOYMENT_TARGET",
         "LANG",
         "LDFLAGS",
         "LDSHARED",

diff --git a/Lib/test/test_concurrent_futures/test_thread_pool.py b/Lib/test/test_concurrent_futures/test_thread_pool.py
@@ -49,6 +49,7 @@ def test_idle_thread_reuse(self):
         self.assertEqual(len(executor._threads), 1)
         executor.shutdown(wait=True)
 
+    @support.requires_fork()
     @unittest.skipUnless(hasattr(os, 'register_at_fork'), 'need os.register_at_fork')
     @support.requires_resource('cpu')
     def test_hang_global_shutdown_lock(self):

diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
@@ -1223,6 +1223,7 @@ def test_collect_garbage(self):
         self.assertEqual(len(gc.garbage), 0)
 
 
+    @requires_subprocess()
     @unittest.skipIf(BUILD_WITH_NDEBUG,
                      'built with -NDEBUG')
     def test_refcount_errors(self):