bpo-8110: Refactor platform detection in subprocess (pythonGH-9053)

Check for functionality via imports rather than checking sys.platform specifically for Windows

Author: zware

Lib/subprocess.py

@@ -41,18 +41,56 @@
  then returns a (exitcode, output) tuple
 """
 
-import sys
-_mswindows = (sys.platform == "win32")
-
+import builtins
+import errno
 import io
 import os
 import time
 import signal
-import builtins
+import sys
+import threading
 import warnings
-import errno
 from time import monotonic as _time
 
+
+__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
+ "getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
+ "SubprocessError", "TimeoutExpired", "CompletedProcess"]
+ # NOTE: We intentionally exclude list2cmdline as it is
+ # considered an internal implementation detail. issue10838.
+
+try:
+ import msvcrt
+ import _winapi
+ _mswindows = True
+except ModuleNotFoundError:
+ _mswindows = False
+ import _posixsubprocess
+ import select
+ import selectors
+else:
+ from _winapi import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,
+ STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,
+ STD_ERROR_HANDLE, SW_HIDE,
+ STARTF_USESTDHANDLES, STARTF_USESHOWWINDOW,
+ ABOVE_NORMAL_PRIORITY_CLASS, BELOW_NORMAL_PRIORITY_CLASS,
+ HIGH_PRIORITY_CLASS, IDLE_PRIORITY_CLASS,
+ NORMAL_PRIORITY_CLASS, REALTIME_PRIORITY_CLASS,
+ CREATE_NO_WINDOW, DETACHED_PROCESS,
+ CREATE_DEFAULT_ERROR_MODE, CREATE_BREAKAWAY_FROM_JOB)
+
+ __all__.extend(["CREATE_NEW_CONSOLE", "CREATE_NEW_PROCESS_GROUP",
+ "STD_INPUT_HANDLE", "STD_OUTPUT_HANDLE",
+ "STD_ERROR_HANDLE", "SW_HIDE",
+ "STARTF_USESTDHANDLES", "STARTF_USESHOWWINDOW",
+ "STARTUPINFO",
+ "ABOVE_NORMAL_PRIORITY_CLASS", "BELOW_NORMAL_PRIORITY_CLASS",
+ "HIGH_PRIORITY_CLASS", "IDLE_PRIORITY_CLASS",
+ "NORMAL_PRIORITY_CLASS", "REALTIME_PRIORITY_CLASS",
+ "CREATE_NO_WINDOW", "DETACHED_PROCESS",
+ "CREATE_DEFAULT_ERROR_MODE", "CREATE_BREAKAWAY_FROM_JOB"])
+
+
 # Exception classes used by this module.
 class SubprocessError(Exception): pass
 
@@ -123,9 +161,6 @@ def stdout(self, value):
 
 
 if _mswindows:
- import threading
- import msvcrt
- import _winapi
  class STARTUPINFO:
  def __init__(self, *, dwFlags=0, hStdInput=None, hStdOutput=None,
  hStdError=None, wShowWindow=0, lpAttributeList=None):
@@ -148,53 +183,6 @@ def copy(self):
  wShowWindow=self.wShowWindow,
  lpAttributeList=attr_list)
 
-else:
- import _posixsubprocess
- import select
- import selectors
- import threading
-
- # When select or poll has indicated that the file is writable,
- # we can write up to _PIPE_BUF bytes without risk of blocking.
- # POSIX defines PIPE_BUF as >= 512.
- _PIPE_BUF = getattr(select, 'PIPE_BUF', 512)
-
- # poll/select have the advantage of not requiring any extra file
- # descriptor, contrarily to epoll/kqueue (also, they require a single
- # syscall).
- if hasattr(selectors, 'PollSelector'):
- _PopenSelector = selectors.PollSelector
- else:
- _PopenSelector = selectors.SelectSelector
-
-
-__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "getstatusoutput",
- "getoutput", "check_output", "run", "CalledProcessError", "DEVNULL",
- "SubprocessError", "TimeoutExpired", "CompletedProcess"]
- # NOTE: We intentionally exclude list2cmdline as it is
- # considered an internal implementation detail. issue10838.
-
-if _mswindows:
- from _winapi import (CREATE_NEW_CONSOLE, CREATE_NEW_PROCESS_GROUP,
- STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,
- STD_ERROR_HANDLE, SW_HIDE,
- STARTF_USESTDHANDLES, STARTF_USESHOWWINDOW,
- ABOVE_NORMAL_PRIORITY_CLASS, BELOW_NORMAL_PRIORITY_CLASS,
- HIGH_PRIORITY_CLASS, IDLE_PRIORITY_CLASS,
- NORMAL_PRIORITY_CLASS, REALTIME_PRIORITY_CLASS,
- CREATE_NO_WINDOW, DETACHED_PROCESS,
- CREATE_DEFAULT_ERROR_MODE, CREATE_BREAKAWAY_FROM_JOB)
-
- __all__.extend(["CREATE_NEW_CONSOLE", "CREATE_NEW_PROCESS_GROUP",
- "STD_INPUT_HANDLE", "STD_OUTPUT_HANDLE",
- "STD_ERROR_HANDLE", "SW_HIDE",
- "STARTF_USESTDHANDLES", "STARTF_USESHOWWINDOW",
- "STARTUPINFO",
- "ABOVE_NORMAL_PRIORITY_CLASS", "BELOW_NORMAL_PRIORITY_CLASS",
- "HIGH_PRIORITY_CLASS", "IDLE_PRIORITY_CLASS",
- "NORMAL_PRIORITY_CLASS", "REALTIME_PRIORITY_CLASS",
- "CREATE_NO_WINDOW", "DETACHED_PROCESS",
- "CREATE_DEFAULT_ERROR_MODE", "CREATE_BREAKAWAY_FROM_JOB"])
 
  class Handle(int):
  closed = False
@@ -215,6 +203,19 @@ def __repr__(self):
 
  __del__ = Close
  __str__ = __repr__
+else:
+ # When select or poll has indicated that the file is writable,
+ # we can write up to _PIPE_BUF bytes without risk of blocking.
+ # POSIX defines PIPE_BUF as >= 512.
+ _PIPE_BUF = getattr(select, 'PIPE_BUF', 512)
+
+ # poll/select have the advantage of not requiring any extra file
+ # descriptor, contrarily to epoll/kqueue (also, they require a single
+ # syscall).
+ if hasattr(selectors, 'PollSelector'):
+ _PopenSelector = selectors.PollSelector
+ else:
+ _PopenSelector = selectors.SelectSelector
 
 
 # This lists holds Popen instances for which the underlying process had not

Misc/NEWS.d/next/Library/2018-09-03-23-54-35.bpo-8110.FExWI_.rst

@@ -0,0 +1,2 @@
+Refactored :mod:`subprocess` to check for Windows-specific modules rather
+than ``sys.platform == 'win32'``.