Issue #11459: A `bufsize` value of 0 in subprocess.Popen() really creates

unbuffered pipes, such that select() works properly on them.

diff --cc Doc/library/platform.rst
Simple merge

diff --cc Lib/os.py
Simple merge

diff --cc Lib/platform.py
index fb65b4ba342c0605f6e6925f7b528a906d5825eb,abe917a4d5f678b2cc81d58e8a4b006ff0159a30..75bc5f3b9799eb7175e4c1ab7177b56308b9a78a
--- 1/Lib/platform.py
--- 2/Lib/platform.py
+++ b/Lib/platform.py
@@@ -357,7 -357,61 +357,7 @@@ def dist(distname='',version='',id=''
                                supported_dists=supported_dists,
                                full_distribution_name=0)
  
- def popen(cmd, mode='r', bufsize=None):
 -class _popen:
 -
 -    """ Fairly portable (alternative) popen implementation.
 -
 -        This is mostly needed in case os.popen() is not available, or
 -        doesn't work as advertised, e.g. in Win9X GUI programs like
 -        PythonWin or IDLE.
 -
 -        Writing to the pipe is currently not supported.
 -
 -    """
 -    tmpfile = ''
 -    pipe = None
 -    bufsize = None
 -    mode = 'r'
 -
 -    def __init__(self,cmd,mode='r',bufsize=None):
 -
 -        if mode != 'r':
 -            raise ValueError('popen()-emulation only supports read mode')
 -        import tempfile
 -        self.tmpfile = tmpfile = tempfile.mktemp()
 -        os.system(cmd + ' > %s' % tmpfile)
 -        self.pipe = open(tmpfile,'rb')
 -        self.bufsize = bufsize
 -        self.mode = mode
 -
 -    def read(self):
 -
 -        return self.pipe.read()
 -
 -    def readlines(self):
 -
 -        if self.bufsize is not None:
 -            return self.pipe.readlines()
 -
 -    def close(self,
 -
 -              remove=os.unlink,error=os.error):
 -
 -        if self.pipe:
 -            rc = self.pipe.close()
 -        else:
 -            rc = 255
 -        if self.tmpfile:
 -            try:
 -                remove(self.tmpfile)
 -            except error:
 -                pass
 -        return rc
 -
 -    # Alias
 -    __del__ = close
 -
+ def popen(cmd, mode='r', bufsize=-1):
  
      """ Portable popen() interface.
      """

diff --cc Lib/subprocess.py
Simple merge

diff --cc Lib/test/test_subprocess.py
index 2dde2458176ff01dea743fcb804228935d71f952,01e670ef72e3f1173f68cf782e63b49fc3cc20b4..6523c8a97ea171f316c8b0a8564b57a1a5a8a1b0
--- 1/Lib/test/test_subprocess.py
--- 2/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@@ -1313,8 -1214,24 +1313,24 @@@ class POSIXProcessTestCase(BaseTestCase
          stdout, stderr = p.communicate()
          self.assertEqual(0, p.returncode, "sigchild_ignore.py exited"
                           " non-zero with this error:\n%s" %
 -                         stderr.decode('utf8'))
 +                         stderr.decode('utf-8'))
  
+     def test_select_unbuffered(self):
+         # Issue #11459: bufsize=0 should really set the pipes as
+         # unbuffered (and therefore let select() work properly).
+         select = support.import_module("select")
+         p = subprocess.Popen([sys.executable, "-c",
+                               'import sys;'
+                               'sys.stdout.write("apple")'],
+                              stdout=subprocess.PIPE,
+                              bufsize=0)
+         f = p.stdout
+         try:
+             self.assertEqual(f.read(4), b"appl")
+             self.assertIn(f, select.select([f], [], [], 0.0)[0])
+         finally:
+             p.wait()
+ 
  
  @unittest.skipUnless(mswindows, "Windows specific tests")
  class Win32ProcessTestCase(BaseTestCase):

diff --cc Misc/NEWS
Simple merge