Issue #11459: A `bufsize` value of 0 in subprocess.Popen() really creates
unbuffered pipes, such that select() works properly on them.
diff --git a/Lib/os.py b/Lib/os.py
index 3ef3db8..a894ee0 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -779,11 +779,13 @@
return bs
# Supply os.popen()
-def popen(cmd, mode="r", buffering=None):
+def popen(cmd, mode="r", buffering=-1):
if not isinstance(cmd, str):
raise TypeError("invalid cmd type (%s, expected string)" % type(cmd))
if mode not in ("r", "w"):
raise ValueError("invalid mode %r" % mode)
+ if buffering == 0 or buffering == None:
+ raise ValueError("popen() does not support unbuffered streams")
import subprocess, io
if mode == "r":
proc = subprocess.Popen(cmd,
diff --git a/Lib/platform.py b/Lib/platform.py
index b01568c..abe917a 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -411,7 +411,7 @@
# Alias
__del__ = close
-def popen(cmd, mode='r', bufsize=None):
+def popen(cmd, mode='r', bufsize=-1):
""" Portable popen() interface.
"""
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 477f927..039b3e6 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -711,8 +711,6 @@
if errread != -1:
errread = msvcrt.open_osfhandle(errread.Detach(), 0)
- if bufsize == 0:
- bufsize = 1 # Nearly unbuffered (XXX for now)
if p2cwrite != -1:
self.stdin = io.open(p2cwrite, 'wb', bufsize)
if self.universal_newlines:
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 3cc387b..01e670e 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1216,6 +1216,22 @@
" non-zero with this error:\n%s" %
stderr.decode('utf8'))
+ 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):