Issue #15204: Deprecated the 'U' mode in file-like objects.
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 78c6dfb..d6eee79 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -62,8 +62,7 @@
'b' binary mode
't' text mode (default)
'+' open a disk file for updating (reading and writing)
- 'U' universal newline mode (for backwards compatibility; unneeded
- for new code)
+ 'U' universal newline mode (deprecated)
========= ===============================================================
The default mode is 'rt' (open for reading text). For binary random
@@ -79,6 +78,10 @@
returned as strings, the bytes having been first decoded using a
platform-dependent encoding or using the specified encoding if given.
+ 'U' mode is deprecated and will raise an exception in future versions
+ of Python. It has no effect in Python 3. Use newline to control
+ universal newlines mode.
+
buffering is an optional integer used to set the buffering policy.
Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
line buffering (only usable in text mode), and an integer > 1 to indicate
@@ -174,6 +177,9 @@
if "U" in modes:
if creating or writing or appending:
raise ValueError("can't use U and writing mode at once")
+ import warnings
+ warnings.warn("'U' mode is deprecated",
+ DeprecationWarning, 2)
reading = True
if text and binary:
raise ValueError("can't have text and binary mode at once")