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/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.
     """