[Python-checkins] cpython: Issue #22389: Add contextlib.redirect_stderr().
berker.peksag
python-checkins at python.org
Fri Nov 28 22:27:35 CET 2014
https://hg.python.org/cpython/rev/7f12c9c09fb6
changeset: 93649:7f12c9c09fb6
user: Berker Peksag <berker.peksag at gmail.com>
date: Fri Nov 28 23:28:06 2014 +0200
summary:
Issue #22389: Add contextlib.redirect_stderr().
files:
Doc/library/contextlib.rst | 10 ++++
Doc/whatsnew/3.5.rst | 9 +++
Lib/contextlib.py | 40 +++++++++++-----
Lib/test/test_contextlib.py | 58 +++++++++++++++---------
Misc/NEWS | 2 +
5 files changed, 85 insertions(+), 34 deletions(-)
diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -172,6 +172,16 @@
.. versionadded:: 3.4
+.. function:: redirect_stderr(new_target)
+
+ Similar to :func:`~contextlib.redirect_stdout` but redirecting
+ :data:`sys.stderr` to another file or file-like object.
+
+ This context manager is :ref:`reentrant <reentrant-cms>`.
+
+ .. versionadded:: 3.5
+
+
.. class:: ContextDecorator()
A base class that enables a context manager to also be used as a decorator.
diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -148,6 +148,15 @@
can now do parallel bytecode compilation.
(Contributed by Claudiu Popa in :issue:`16104`.)
+contextlib
+----------
+
+* The new :func:`contextlib.redirect_stderr` context manager(similar to
+ :func:`contextlib.redirect_stdout`) makes it easier for utility scripts to
+ handle inflexible APIs that write their output to :data:`sys.stderr` and
+ don't provide any options to redirect it.
+ (Contributed by Berker Peksag in :issue:`22389`.)
+
doctest
-------
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -5,7 +5,7 @@
from functools import wraps
__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
- "redirect_stdout", "suppress"]
+ "redirect_stdout", "redirect_stderr", "suppress"]
class ContextDecorator(object):
@@ -151,8 +151,27 @@
def __exit__(self, *exc_info):
self.thing.close()
-class redirect_stdout:
- """Context manager for temporarily redirecting stdout to another file
+
+class _RedirectStream:
+
+ _stream = None
+
+ def __init__(self, new_target):
+ self._new_target = new_target
+ # We use a list of old targets to make this CM re-entrant
+ self._old_targets = []
+
+ def __enter__(self):
+ self._old_targets.append(getattr(sys, self._stream))
+ setattr(sys, self._stream, self._new_target)
+ return self._new_target
+
+ def __exit__(self, exctype, excinst, exctb):
+ setattr(sys, self._stream, self._old_targets.pop())
+
+
+class redirect_stdout(_RedirectStream):
+ """Context manager for temporarily redirecting stdout to another file.
# How to send help() to stderr
with redirect_stdout(sys.stderr):
@@ -164,18 +183,13 @@
help(pow)
"""
- def __init__(self, new_target):
- self._new_target = new_target
- # We use a list of old targets to make this CM re-entrant
- self._old_targets = []
+ _stream = "stdout"
- def __enter__(self):
- self._old_targets.append(sys.stdout)
- sys.stdout = self._new_target
- return self._new_target
- def __exit__(self, exctype, excinst, exctb):
- sys.stdout = self._old_targets.pop()
+class redirect_stderr(_RedirectStream):
+ """Context manager for temporarily redirecting stderr to another file."""
+
+ _stream = "stderr"
class suppress:
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -718,60 +718,76 @@
stack.push(cm)
self.assertIs(stack._exit_callbacks[-1], cm)
-class TestRedirectStdout(unittest.TestCase):
+
+class TestRedirectStream:
+
+ redirect_stream = None
+ orig_stream = None
@support.requires_docstrings
def test_instance_docs(self):
# Issue 19330: ensure context manager instances have good docstrings
- cm_docstring = redirect_stdout.__doc__
- obj = redirect_stdout(None)
+ cm_docstring = self.redirect_stream.__doc__
+ obj = self.redirect_stream(None)
self.assertEqual(obj.__doc__, cm_docstring)
def test_no_redirect_in_init(self):
- orig_stdout = sys.stdout
- redirect_stdout(None)
- self.assertIs(sys.stdout, orig_stdout)
+ orig_stdout = getattr(sys, self.orig_stream)
+ self.redirect_stream(None)
+ self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
def test_redirect_to_string_io(self):
f = io.StringIO()
msg = "Consider an API like help(), which prints directly to stdout"
- orig_stdout = sys.stdout
- with redirect_stdout(f):
- print(msg)
- self.assertIs(sys.stdout, orig_stdout)
+ orig_stdout = getattr(sys, self.orig_stream)
+ with self.redirect_stream(f):
+ print(msg, file=getattr(sys, self.orig_stream))
+ self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
s = f.getvalue().strip()
self.assertEqual(s, msg)
def test_enter_result_is_target(self):
f = io.StringIO()
- with redirect_stdout(f) as enter_result:
+ with self.redirect_stream(f) as enter_result:
self.assertIs(enter_result, f)
def test_cm_is_reusable(self):
f = io.StringIO()
- write_to_f = redirect_stdout(f)
- orig_stdout = sys.stdout
+ write_to_f = self.redirect_stream(f)
+ orig_stdout = getattr(sys, self.orig_stream)
with write_to_f:
- print("Hello", end=" ")
+ print("Hello", end=" ", file=getattr(sys, self.orig_stream))
with write_to_f:
- print("World!")
- self.assertIs(sys.stdout, orig_stdout)
+ print("World!", file=getattr(sys, self.orig_stream))
+ self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
s = f.getvalue()
self.assertEqual(s, "Hello World!\n")
def test_cm_is_reentrant(self):
f = io.StringIO()
- write_to_f = redirect_stdout(f)
- orig_stdout = sys.stdout
+ write_to_f = self.redirect_stream(f)
+ orig_stdout = getattr(sys, self.orig_stream)
with write_to_f:
- print("Hello", end=" ")
+ print("Hello", end=" ", file=getattr(sys, self.orig_stream))
with write_to_f:
- print("World!")
- self.assertIs(sys.stdout, orig_stdout)
+ print("World!", file=getattr(sys, self.orig_stream))
+ self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
s = f.getvalue()
self.assertEqual(s, "Hello World!\n")
+class TestRedirectStdout(TestRedirectStream, unittest.TestCase):
+
+ redirect_stream = redirect_stdout
+ orig_stream = "stdout"
+
+
+class TestRedirectStderr(TestRedirectStream, unittest.TestCase):
+
+ redirect_stream = redirect_stderr
+ orig_stream = "stderr"
+
+
class TestSuppress(unittest.TestCase):
@support.requires_docstrings
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -191,6 +191,8 @@
Library
-------
+- Issue #22389: Add contextlib.redirect_stderr().
+
- Issue #21356: Make ssl.RAND_egd() optional to support LibreSSL. The
availability of the function is checked during the compilation. Patch written
by Bernard Spil.
--
Repository URL: https://hg.python.org/cpython
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