Fixes issue #17488: Change the subprocess.Popen bufsize parameter default value
from unbuffered (0) to buffering (-1) to match the behavior existing code
expects and match the behavior of the subprocess module in Python 2 to avoid
introducing hard to track down bugs.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 7cfe5df..7255645 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -25,7 +25,7 @@
===========================
This module defines one class called Popen:
-class Popen(args, bufsize=0, executable=None,
+class Popen(args, bufsize=-1, executable=None,
stdin=None, stdout=None, stderr=None,
preexec_fn=None, close_fds=True, shell=False,
cwd=None, env=None, universal_newlines=False,
@@ -56,12 +56,12 @@
way: The list2cmdline is designed for applications using the same
rules as the MS C runtime.
-bufsize, if given, has the same meaning as the corresponding argument
-to the built-in open() function: 0 means unbuffered, 1 means line
-buffered, any other positive value means use a buffer of
-(approximately) that size. A negative bufsize means to use the system
-default, which usually means fully buffered. The default value for
-bufsize is 0 (unbuffered).
+bufsize will be supplied as the corresponding argument to the io.open()
+function when creating the stdin/stdout/stderr pipe file objects:
+0 means unbuffered (read & write are one system call and can return short),
+1 means line buffered, any other positive value means use a buffer of
+approximately that size. A negative bufsize, the default, means the system
+default of io.DEFAULT_BUFFER_SIZE will be used.
stdin, stdout and stderr specify the executed programs' standard
input, standard output and standard error file handles, respectively.
@@ -638,7 +638,7 @@
class Popen(object):
- def __init__(self, args, bufsize=0, executable=None,
+ def __init__(self, args, bufsize=-1, executable=None,
stdin=None, stdout=None, stderr=None,
preexec_fn=None, close_fds=_PLATFORM_DEFAULT_CLOSE_FDS,
shell=False, cwd=None, env=None, universal_newlines=False,
@@ -650,7 +650,7 @@
self._child_created = False
if bufsize is None:
- bufsize = 0 # Restore default
+ bufsize = -1 # Restore default
if not isinstance(bufsize, int):
raise TypeError("bufsize must be an integer")