bpo-32236: open() emits RuntimeWarning if buffering=1 for binary mode (GH-4842)

If buffering=1 is specified for open() in binary mode, it is silently
treated as buffering=-1 (i.e., the default buffer size).
Coupled with the fact that line buffering is always supported in Python 2,
such behavior caused several issues (e.g., bpo-10344, bpo-21332).

Warn that line buffering is not supported if open() is called with
binary mode and buffering=1.

1 files changed, 2 insertions, 2 deletions

diff --git a/Lib/test/test_cmd_line_script.py b/Lib/test/test_cmd_line_script.py
index 5ec9bbb..bc812ea 100644
--- a/Lib/test/test_cmd_line_script.py
+++ b/Lib/test/test_cmd_line_script.py
@@ -169,10 +169,10 @@ class CmdLineTest(unittest.TestCase):
     @contextlib.contextmanager
     def interactive_python(self, separate_stderr=False):
         if separate_stderr:
-            p = spawn_python('-i', bufsize=1, stderr=subprocess.PIPE)
+            p = spawn_python('-i', stderr=subprocess.PIPE)
             stderr = p.stderr
         else:
-            p = spawn_python('-i', bufsize=1, stderr=subprocess.STDOUT)
+            p = spawn_python('-i', stderr=subprocess.STDOUT)
             stderr = p.stdout
         try:
             # Drain stderr until prompt