Issue #11459: A `bufsize` value of 0 in subprocess.Popen() really creates
unbuffered pipes, such that select() works properly on them.
diff --git a/Doc/library/platform.rst b/Doc/library/platform.rst
index 56518f7..a71d533 100644
--- a/Doc/library/platform.rst
+++ b/Doc/library/platform.rst
@@ -205,7 +205,7 @@
Win95/98 specific
^^^^^^^^^^^^^^^^^
-.. function:: popen(cmd, mode='r', bufsize=None)
+.. function:: popen(cmd, mode='r', bufsize=-1)
Portable :func:`popen` interface. Find a working popen implementation
preferring :func:`win32pipe.popen`. On Windows NT, :func:`win32pipe.popen`
diff --git a/Lib/os.py b/Lib/os.py
index aa1a40f..b46c02f 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -629,11 +629,13 @@
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 2294604..dd09460 100755
--- a/Lib/platform.py
+++ b/Lib/platform.py
@@ -398,7 +398,7 @@
# 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 97792db..dc5b608 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -653,8 +653,6 @@
if errread is not None:
errread = msvcrt.open_osfhandle(errread.Detach(), 0)
- if bufsize == 0:
- bufsize = 1 # Nearly unbuffered (XXX for now)
if p2cwrite is not None:
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 c781904..410849f 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -864,6 +864,21 @@
def prepare():
raise ValueError("surrogate:\uDCff")
+ 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()
#
# Windows tests
diff --git a/Misc/NEWS b/Misc/NEWS
index f18e557..be44a06 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -40,6 +40,9 @@
Library
-------
+- Issue #11459: A ``bufsize`` value of 0 in subprocess.Popen() really creates
+ unbuffered pipes, such that select() works properly on them.
+
- Issue #5421: Fix misleading error message when one of socket.sendto()'s
arguments has the wrong type. Patch by Nikita Vetoshkin.