bpo-40094: Add os.waitstatus_to_exitcode() (GH-19201)

Add os.waitstatus_to_exitcode() function to convert a wait status to an
exitcode.

Suggest waitstatus_to_exitcode() usage in the documentation when
appropriate.

Use waitstatus_to_exitcode() in:

* multiprocessing, os, subprocess and _bootsubprocess modules;
* test.support.wait_process();
* setup.py: run_command();
* and many tests.

1 files changed, 2 insertions, 6 deletions

diff --git a/Lib/os.py b/Lib/os.py
index 8459baa..8acd6f1 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -864,12 +864,8 @@ if _exists("fork") and not _exists("spawnv") and _exists("execv"):
                 wpid, sts = waitpid(pid, 0)
                 if WIFSTOPPED(sts):
                     continue
-                elif WIFSIGNALED(sts):
-                    return -WTERMSIG(sts)
-                elif WIFEXITED(sts):
-                    return WEXITSTATUS(sts)
-                else:
-                    raise OSError("Not stopped, signaled or exited???")
+
+                return waitstatus_to_exitcode(sts)
 
     def spawnv(mode, file, args):
         """spawnv(mode, file, args) -> integer