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

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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.
This commit is contained in:
Alexey Izbyshev 2018-10-20 03:22:31 +03:00 • committed by Victor Stinner
parent 4acf6c9d4b
commit a2670565d8
11 changed files with 88 additions and 28 deletions
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5
Lib/_pyio.py
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@ -198,6 +198,11 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
raise ValueError("binary mode doesn't take an errors argument")
if binary and newline is not None:
raise ValueError("binary mode doesn't take a newline argument")
if binary and buffering == 1:
import warnings
warnings.warn("line buffering (buffering=1) isn't supported in binary "
"mode, the default buffer size will be used",
RuntimeWarning, 2)
raw = FileIO(file,
(creating and "x" or "") +
(reading and "r" or "") +