Add unicode_std_stream function to write UTF-8 to stdout/stderr

IPython/utils/io.py

@@ -10,15 +10,17 b' IO related utilities.'
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 from __future__ import print_function
+from __future__ import absolute_import
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
+import codecs
 import os
 import sys
 import tempfile
 from .capture import CapturedIO, capture_output
-from .py3compat import string_types, input
+from .py3compat import string_types, input, PY3
 
 #-----------------------------------------------------------------------------
 # Code
@@ -227,3 +229,26 b' def raw_print_err(*args, **kw):'
 # Short aliases for quick debugging, do NOT use these in production code.
 rprint = raw_print
 rprinte = raw_print_err
+
+def unicode_std_stream(stream='stdout'):
+    """Get a wrapper to write unicode to stdout/stderr as UTF-8.
+
+    This ignores environment variables and default encodings, to reliably write
+    unicode to stdout or stderr.
+
+    ::
+
+        unicode_std_stream().write(u'ł@e¶ŧ←')
+    """
+    assert stream in ('stdout', 'stderr')
+    stream  = getattr(sys, stream)
+    if PY3:
+        try:
+            stream_b = stream.buffer
+        except AttributeError:
+            # sys.stdout has been replaced - use it directly
+            return stream
+    else:
+        stream_b = stream
+
+    return codecs.getwriter('utf-8')(stream_b)

IPython/utils/tests/test_io.py

@@ -12,7 +12,9 b''
 # Imports
 #-----------------------------------------------------------------------------
 from __future__ import print_function
+from __future__ import absolute_import
 
+import io as stdlib_io
 import sys
 
 from subprocess import Popen, PIPE
@@ -20,7 +22,8 b' import unittest'
 
 import nose.tools as nt
 
-from IPython.utils.io import Tee, capture_output
+from IPython.testing.decorators import skipif
+from IPython.utils.io import Tee, capture_output, unicode_std_stream
 from IPython.utils.py3compat import doctest_refactor_print, PY3
 
 if PY3:
@@ -88,3 +91,34 b' def test_capture_output():'
     
     nt.assert_equal(io.stdout, 'hi, stdout\n')
     nt.assert_equal(io.stderr, 'hi, stderr\n')
+
+def test_UnicodeStdStream():
+    # Test wrapping a bytes-level stdout
+    if PY3:
+        stdoutb = stdlib_io.BytesIO()
+        stdout = stdlib_io.TextIOWrapper(stdoutb, encoding='ascii')
+    else:
+        stdout = stdoutb = stdlib_io.BytesIO()
+
+    orig_stdout = sys.stdout
+    sys.stdout = stdout
+    try:
+        sample = u"@łe¶ŧ←"
+        unicode_std_stream().write(sample)
+
+        output = stdoutb.getvalue().decode('utf-8')
+        nt.assert_equal(output, sample)
+        assert not stdout.closed
+    finally:
+        sys.stdout = orig_stdout
+
+@skipif(not PY3, "Not applicable on Python 2")
+def test_UnicodeStdStream_nowrap():
+    # If we replace stdout with a StringIO, it shouldn't get wrapped.
+    orig_stdout = sys.stdout
+    sys.stdout = StringIO()
+    try:
+        nt.assert_is(unicode_std_stream(), sys.stdout)
+        assert not sys.stdout.closed
+    finally:
+        sys.stdout = orig_stdout
  No newline at end of file