bpo-30082 Popen: add kwarg to hide process window on Windows

Doc/library/subprocess.rst

@@ -360,7 +360,7 @@ functions.
                  start_new_session=False, pass_fds=(), *, group=None, \
                  extra_groups=None, user=None, umask=-1, \
                  encoding=None, errors=None, text=None, pipesize=-1, \
-                 process_group=None)
+                 process_group=None, force_hide=False)
 
    Execute a child program in a new process.  On POSIX, the class uses
    :meth:`os.execvpe`-like behavior to execute the child program.  On Windows,
@@ -457,6 +457,10 @@ functions.
    into the shell (e.g. :command:`dir` or :command:`copy`).  You do not need
    ``shell=True`` to run a batch file or console-based executable.
 
+   On Windows, ``force_hide=True`` attempts to start the application without creating
+   or showing any windows. Some applications may ignore this request, and applications
+   that are hidden often cannot be used or exited by users.
+
    .. note::
 
       Read the `Security Considerations`_ section before using ``shell=True``.

Lib/subprocess.py

@@ -843,6 +843,8 @@ class Popen:
 
       startupinfo and creationflags (Windows only)
 
+      force_hide (Windows only)
+
       restore_signals (POSIX only)
 
       start_new_session (POSIX only)
@@ -875,7 +877,8 @@ def __init__(self, args, bufsize=-1, executable=None,
                  restore_signals=True, start_new_session=False,
                  pass_fds=(), *, user=None, group=None, extra_groups=None,
                  encoding=None, errors=None, text=None, umask=-1, pipesize=-1,
-                 process_group=None):
+                 process_group=None,
+                 force_hide=False):
         """Create new Popen instance."""
         if not _can_fork_exec:
             raise OSError(
@@ -920,6 +923,9 @@ def __init__(self, args, bufsize=-1, executable=None,
             if creationflags != 0:
                 raise ValueError("creationflags is only supported on Windows "
                                  "platforms")
+            if force_hide:
+                raise ValueError("force_hide is only supported on Windows "
+                                 "platforms")
 
         self.args = args
         self.stdin = None
@@ -1097,7 +1103,9 @@ def __init__(self, args, bufsize=-1, executable=None,
                                 errread, errwrite,
                                 restore_signals,
                                 gid, gids, uid, umask,
-                                start_new_session, process_group)
+                                start_new_session,
+                                process_group,
+                                force_hide)
         except:
             # Cleanup if the child failed starting.
             for f in filter(None, (self.stdin, self.stdout, self.stderr)):
@@ -1510,7 +1518,8 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                            unused_restore_signals,
                            unused_gid, unused_gids, unused_uid,
                            unused_umask,
-                           unused_start_new_session, unused_process_group):
+                           unused_start_new_session, unused_process_group,
+                           force_hide):
             """Execute program (MS Windows version)"""
 
             assert not pass_fds, "pass_fds not supported on Windows."
@@ -1574,9 +1583,24 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                     # the ones in the handle_list
                     close_fds = False
 
-            if shell:
+            if force_hide or shell:
+                # We pass SW_HIDE to the process so that it will not display any
+                # window even if it normally would.
                 startupinfo.dwFlags |= _winapi.STARTF_USESHOWWINDOW
                 startupinfo.wShowWindow = _winapi.SW_HIDE
+
+            if force_hide and not (creationflags & _winapi.DETACHED_PROCESS):
+                # If the child process is flagged as SUBSYSTEM_CONSOLE, then
+                # it either inherits the console of its parent, if the parent
+                # has one, or allocates a new console. An inherited console may
+                # be visible even if SW_HIDE is set. By setting the creation
+                # flag CREATE_NEW_CONSOLE, the child is forced to allocate a
+                # new console that will have a hidden window.
+                # Note: CREATE_NEW_CONSOLE cannot be used with DETACHED_PROCESS.
+                creationflags |= _winapi.CREATE_NEW_CONSOLE
+
+            if shell:
+                comspec = os.environ.get("COMSPEC", "cmd.exe")
                 if not executable:
                     # gh-101283: without a fully-qualified path, before Windows
                     # checks the system directories, it first looks in the
@@ -1884,7 +1908,8 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
                            errread, errwrite,
                            restore_signals,
                            gid, gids, uid, umask,
-                           start_new_session, process_group):
+                           start_new_session, process_group,
+                           unused_force_hide):
             """Execute program (POSIX version)"""
 
             if isinstance(args, (str, bytes)):

Lib/test/test_subprocess.py

@@ -58,6 +58,11 @@
     raise unittest.SkipTest("test module requires subprocess")
 
 mswindows = (sys.platform == "win32")
+if mswindows:
+    try:
+        import ctypes
+    except ImportError:
+        ctypes = None
 
 #
 # Depends on the following external programs: Python
@@ -2509,6 +2514,10 @@ def test_invalid_args(self):
                           [sys.executable, "-c",
                            "import sys; sys.exit(47)"],
                           creationflags=47)
+        self.assertRaises(ValueError, subprocess.call,
+                          [sys.executable, "-c",
+                           "import sys; sys.exit(47)"],
+                          force_hide=47)
 
     def test_shell_sequence(self):
         # Run command through the shell (sequence)
@@ -3693,12 +3702,23 @@ def test_startupinfo_copy(self):
             self.assertEqual(startupinfo.lpAttributeList, {"handle_list": []})
 
     def test_creationflags(self):
-        # creationflags argument
-        CREATE_NEW_CONSOLE = 16
         sys.stderr.write("    a DOS box should flash briefly ...\n")
         subprocess.call(sys.executable +
                         ' -c "import time; time.sleep(0.25)"',
-                        creationflags=CREATE_NEW_CONSOLE)
+                        creationflags=subprocess.CREATE_NEW_CONSOLE)
+
+    def test_force_hide(self):
+        if ctypes:
+            script = textwrap.dedent(r'''
+                import sys, ctypes
+                GetConsoleWindow = ctypes.WinDLL('kernel32').GetConsoleWindow
+                IsWindowVisible = ctypes.WinDLL('user32').IsWindowVisible
+                sys.exit(IsWindowVisible(GetConsoleWindow()))
+            ''')
+        else:
+            script = 'import sys; sys.exit(0)'
+        rc = subprocess.call([sys.executable, '-c', script], force_hide=True)
+        self.assertEqual(rc, 0)
 
     def test_invalid_args(self):
         # invalid arguments should raise ValueError

Misc/NEWS.d/next/Windows/2021-10-29-15-02-46.bpo-30082.VhSkKB.rst

@@ -0,0 +1,3 @@
+Adds new ``force_hide`` argument to :mod:`subprocess` functions.
+This passes ``SW_HIDE`` to the new process, which most applications
+will use to not display any window even if they normally would.